THE CLEMENTINE NIR GLOBAL LUNAR
MOSAIC
Lisa Gaddis, Chris Isbell, Matt Staid*, Eric
Eliason**,
Ella Mae Lee, Lynn Weller, and Tracie
Sucharski
Astrogeology Team
Paul Lucey, Dave
Blewett***, John Hinrichs***, Donovan Steutel
Hawaii Institute of Geophysics and
Planetology
May 1, 2007
Version 0.1
* Now at Planetary Sciences Institute
1700 East
** Now at Planetary Image Research Laboratory
Lunar and Planetary Laboratory
Department of Planetary Sciences
The
*** Now at NovaSol
Return to CD Home Page
3 - NEAR-INFRARED (NIR) CAMERA
8 - PHOTOMETRIC FUNCTION NORMALIZATION
9 - EMPIRICAL FRAME-OFFSET CORRECTION
10 - CONVERSION OF 16-BIT PIXEL VALUES TO FLOATING
POINT NUMBERS
11 - FILES, DIRECTORIES, AND DISK CONTENTS
APPENDIX A - KEYWORD ASSIGNMENTS
APPENDIX B - GEOMETRIC DEFINITION OF A PIXEL
1 - INTRODUCTION
The Clementine
Near-Infrared (NIR) mosaic [Eliason
et al., 2003; Staid et al., 2003] of Earth's Moon is a
radiometrically and geometrically controlled, photometrically modeled global mosaicked
Digital Image Model (DIM) [Batson, 1987; Batson, 1990]. The
NIR DIM was compiled using more than 400,000 images from the Near-Infrared
Camera onboard the Clementine orbiting spacecraft. The mosaic is produced in six wavelengths with
band centers at 1100, 1250, 1500, 2000, 2600, and 2780 nanometers (nm). Cartographic processing of the NIR mosaic
resembles that applied to the mosaic derived from data acquired by the
five-band (415, 750, 900, 950, 1000 nm) Ultraviolet/Visible (UVVIS) Camera that
also flew onboard the Clementine orbiter [e.g., Eliason et al., 1999]. The
major lunar rock-forming minerals plagioclase, pyroxene, and olivine have
diagnostic absorptions in this wavelength range, so the NIR data combined with
UVVIS data can be used to characterize aspects of the mineralogic and lithologic
diversity of the Moon [e.g., Le Mouelic
et al., 1999; Gillis et al., 2004).
These UVVIS and NIR multispectral data are complemented by data acquired
by two additional Clementine science cameras, the High Resolution (HIRES)
[e.g., Robinson et al., 2003] and
Long-Wavelength Infrared (LWIR) instruments [e.g., Lawson et al., 2000].
The NIR mosaic is
mapped in the Sinusoidal Equal-Area Projection [Snyder, 1987] at a
resolution of 100 meters per pixel and requires approximately 68 gigabytes of
digital storage. This database is
partitioned into 996 quadrangles (quads) or "tiles" equivalent to
those of the previously released Clementine 750 nanometer Basemap Mosaic (PDS
volumes CL_3001 through CL_3015) and the UVVIS DIM (PDS volumes CL_4001 through
CL_4078; Eliason et al., 1999). This 100 m/pixel version of the NIR DIM is presented
on 13 DVD volumes (equivalent to 78 ‘virtual CD’ volumes). Tiles are
stored as image files of approximately 2100 pixels on a side, covering
approximately a 6-degree by 7-degree quadrangle (303 pixels/degree). Pixels are
16-bit signed integers. Reduced-resolution planet-wide NIR
mosaics will be made available online at the PDS Map-a-Planet Web site (http://www.mapaplanet.org) along with the
full-resolution NIR mosaic. Additional
information in support of the NIR DIM, including a frame number (colorset_id) image,
empirical frame offset values for each frame, and a source file index table ('srcindx.tab')
will be made available online at http://astrogeology.usgs.gov/Projects/ClementineNIR/. The source file index table contains
information about the Engineering Data Record (EDR) image collection used to
assemble the NIR DIM and the images that make up 6-band color sets. This file contains an entry for each EDR
image that was used in this database. A phase
angle image database does not accompany the NIR DIM (recall that this
information is available with the UVVIS DIM archive).
Although the tiling
scheme is identical to the original basemap, each 30-degree longitudinal section
of the basemap now represents one DVD volume (equivalent to 6 virtual CD
volumes). The full-resolution tiling and
archive scheme is available in graphical form in the 'scheme.pdf' (Portable
Document Format [PDF]) file found in the 'document' directory of each volume.
PDS standards
require inclusion of "catalog" files that describe aspects of the
mission, spacecraft, instrument, and dataset.
These files are located in the 'catalog' directory of each CD volume. To minimize the amount of redundant
information we reference these files throughout this document. The catalog files, ending with the '.cat'
extension, are organized as ASCII text files and contain PDS labels for
automatically ingesting the documents into a catalog system.
The DVD volume set
contains ancillary data files that support the NIR mosaic. These files include browse images stored in a
'JPEG' format, 'HTML' documents that support a web browser interface to the volumes,
image index files that tabulate the contents of the volume set, and
documentation files that describe the archive collection. For more information on the contents and
organization of the volume set, refer to the "Files, Directories, and Disk
Contents" section of this document.
Using a web browser
application (e.g., Netscape or MS Internet Explorer), open the 'index.htm' file located in the 'root' directory of each CD. The html document will direct you to other
informational documents and the image browser for rapidly viewing the image
collection.
The browse image
consists of false color and color ratio images for each Clementine NIR DIM
product. Three browse image renditions
are available to the user: false color, color ratio, and black-and-white 2000
nm images. The false color images use
the 1100 nm (blue), 1500 nm (green), and 2000 nm (red) spectral bands to
portray the Moon in enhanced color. The
color ratio browse images use the 1500/1100 (blue), 1500/2000 (green), and 1500
(red). The ratio rendition enhances
color differences related to soil mineralogy as measured by reflectance at the
given wavelengths. At NIR wavelengths,
the ratios measure strength of absorption bands of common lunar minerals such
as orthopyroxene, clinopyroxene, olivine, and plagioclase [e.g., Pieters, 1993]. In particular, the 1500/1100 nm ratio is
sensitive to the abundance of clinopyroxene and olivine, as well as plagioclase,
and the 1500/2000 nm ratio is related to the abundance of pyroxene in lunar
soil. The NIR data are particularly
useful for discriminating between olivine and pyroxene because pyroxene has two
absorptions in the UVVIS and NIR (near 1 and 2 microns, or 1000 and 2000 nm)
and olivine has only one (near 1 micron, or 1000 nm).
Software tools for
viewing and accessing the image collection are available through the Planetary
Data System (PDS) Internet services. Refer
to the 'aareadme.txt' located in
the 'root' for more information
on these tools. The program NASAView can be used to display the
full resolution NIR image products. NASAView is a PDS product display tool
that runs on multiple platforms with a common graphical user interface. The current version (version 2.13, 2006) supports
the display of multi-band image cubes (up to three selected bands). See the PDS Software Download page (http://pds.jpl.nasa.gov/tools/software_download.cfm)
for information on NASAView and
its availability.
Another tool,
Map-a-Planet (MAP), provides online access to the NIR data via the MapMaker software. Map-a-Planet allows users to generate
seamless image maps for any latitude-longitude region of the Moon at a variety
of scales and map projections. For more
information on Map-a-Planet and the MapMaker system, refer to the USGS
Astrogeology Program Web page at http://www.mapaplanet.org/ .
Additionally, each
image file is associated with an Integrated Software for Imagers and
Spectrometers (
Go
to Table of Contents.
2 - CLEMENTINE
The Clementine
Mission [Nozette et al., 1994;
McEwen and Robinson, 1997], officially known as the Deep Space Program Science Experiment (DSPSE),
was the first in a planned series of technology demonstrations jointly
sponsored by the Ballistic Missile Defense Organization (BMDO) of the
Department of Defense and the National Aeronautics and Space Administration
(NASA). The spacecraft was known as
Clementine because, as in the song of the same name, it would be 'lost and gone
forever' after completing its short mission.
Clementine was launched on 1994-01-25 onboard a Titan IIG rocket from
Vandenburg Air Force Base in
Clementine's primary
objective was to qualify lightweight imaging sensors and component technologies
(including a star tracker, inertial measurement unit, reaction wheel, nickel
hydrogen battery, and solar panel) for the next generation of Department of
Defense spacecraft. DSPSE represented a
new class of small, low cost, and highly capable spacecraft that embraced
emerging lightweight technologies to enable future long-duration deep space
missions. A second objective of
Clementine was the return of scientific data about the Moon and asteroid Geographos
to the international civilian space community.
The NIR mosaic was
created using data from Clementine EDR Image Archive [e.g., Eliason et al.,
1995] produced by the Clementine mission. The EDR (Engineering Data Record) data are raw
images that contain the inherent properties of unprocessed and uncorrected data
[Lewis, 1995]. The Clementine EDR Image Archive contains
more than 1.9 million images acquired during active mission operations. For information on how to obtain this archive
contact NSSDC (http://nssdc.gsfc.nasa.gov/database/MasterCatalog?ds=PSPG-00309)
or the PDS Imaging Node Clementine Mission pages (http://pdsimg.jpl.nasa.gov/Missions/Clementine_mission.html).
Go
to Table of Contents.
3 - NEAR-INFRARED (NIR) CAMERA
The Clementine
Near-Infrared (NIR) camera was a framing camera built jointly by Lawrence
Livermore National Laboratory (LLNL) and Amber Engineering of
Go
to Table of Contents.
4 - LUNAR ORBIT SUMMARY
The Clementine
spacecraft maintained a polar orbit during the systematic mapping of the
surface of the Moon [McEwen and
Robinson, 1997]. Mapping of
the lunar surface was done in two Earth months, or two lunar days. To obtain full coverage during these two
months, the image overlap for both the UVVIS and NIR cameras was ~15% in the
down-track and ~10% in the cross-track directions. This mapping scheme required an inclination of
the orbit of 90 degrees plus-or-minus 1.0 degree with reference to the lunar
equator; the periselene of the lunar orbit was maintained at an altitude of 425
plus-or-minus 25 km. To provide the
necessary cross-track separation for the alternating imaging strips to cover
the entire surface of the Moon, the orbital period was approximately 5 hours,
during which the Moon rotated approximately 2.7 degrees beneath the spacecraft. Images were taken and recorded only in the region
of periselene, leaving sufficient time to replay the data to Earth.
The best data for
lunar mineral mapping are obtained if both high and low solar phase angles are
avoided, nominally at angles less than 30 and greater than 0 degrees. The solar phase angle is defined as the angle
between the vector to the Sun and the vector to the spacecraft from a point on
the Moon's surface. To maximize the time
in which the solar phase angle is less than 30 degrees, the plane of the lunar
orbit should contain the Moon-Sun line halfway through the two-month lunar
mapping period. Therefore, insertion
into the lunar orbit was selected so that, as the Moon-Sun line changes with
Earth's motion about the Sun, the Moon-Sun line will initially close on the
orbital plane, and then lie in the orbital plane halfway through the mapping
mission. The angle between the Moon-Sun
line and the orbital plane was near-zero (less than 5 degrees) for
approximately five weeks before becoming zero. The table below lists Clementine's orbital
parameters. For more information on the
lunar orbit refer to the 'mission.cat'
file located in the 'catalog'
directory.
Clementine Orbital Parameters
================================================================
Orbital Period: 4.970
hr < P < 5.003 hr
Altitude of
Periselene: 401 km < radius < 451
km
Eccentricity: 0.35821 < e < 0.37567
Right
Ascension: -3 deg
< Omega < +3 deg (J2000)
Inclination: 89 deg
< i < 91 deg
Argument of
Periselene: -28.4 deg < w < -27.9
deg (1st month)
29.2
deg < w < 29.6 deg (2nd month)
Go
to Table of Contents.
5 - GEOMETRIC ACCURACY
Both the Clementine NIR
and UVVIS mosaics were geometrically controlled to the previously published 750-nm
Clementine Basemap Mosaic [PDS volumes CL_3001 through CL_3015] by tying
individual NIR images that make up a color set to the corresponding image used
to produce the basemap mosaic. The 750-nm
basemap mosaic was geometrically controlled using the methods described below.
Although shortcomings
have since been identified [e.g., Cook et
al., 2002], the 750-nm basemap mosaic
significantly improved the geometric control of the Moon from previous maps and
ground control points. On the basis of
best-effort measurements of the spacecraft orbit and pointing, UVVIS geometric
distortions, and time tags for each observation, the Clementine Spacecraft,
Planet Instrument, C-matrix, and Event kernels [SPICE;
The geometric
processing goal of the basemap was for 95% of the Moon (excluding the oblique
observation gap fills) to have better than 0.5 km/pixel absolute positional
accuracy and to adjust the camera angles so that all frames match neighboring
frames to within an accuracy of 2 pixels [e.g.,
Lee et al., 1997; Eliason et al., 1998, Isbell et al., 1999]. To achieve these goals, camera alignment and
pointing data were required to be accurate to a few hundredths of a degree. The absolute alignment of the UVVIS was
determined with respect to spacecraft-fixed axes (A and B Star Tracker Camera
quaternions) by analyzing a major subset of the over 17,000 images of Vega,
over 6,000 images of the Southern Cross, and a few hundred images of the
Pleiades, taken during the approach to the Moon and throughout the lunar
mapping phase of the Clementine mission. Multiple star images within a single picture
were used to determine the UVVIS focal length and optical distortion parameter
values.
Approximately
265,000 match points were collected at the USGS from ~43,000 UVVIS 750 nm
images providing global coverage [e.g.,
Lee et al., 1997]. Approximately 80%
of these points were collected via autonomous procedures, and the remaining 20%
were collected manually. Streamlined
procedures for the supervised collection of match points were developed and
applied, and these procedures saved several person-years of effort. The automated success rate exceeded 90% along
each spacecraft orbit track, where the overlap regions of successive images are
highly correlated, but failed when the overlap region is narrow and/or nearly
featureless. ('Failure' is defined as
less than 3 points per image with correlation coefficients greater than 0.85;
thus, many good match points were rejected because we could not be certain that
the matches were valid without verification.) Across-track matching was more
difficult due to changes in scale and illumination angle, but a fair success
rate (~60%) was achieved via the use of 'window-shaping' (local geometric
reprojections). The oblique gap-fill
images were the most difficult to match and required substantial human
intervention. Matching the polar regions
was time-consuming because each frame overlaps many other frames. Most match point locations were found to a
precision of 0.2 pixel.
The USGS match
points were provided to Tim Colvin and Mert Davies of the RAND Corporation for
analytical triangulations. Using these
match points, control points from the Apollo region, and the latest SPICE
kernels from Navigation and Ancillary Information Facility (NAIF) at JPL [
Go
to Table of Contents.
6 - DATA PROCESSING
As was the case for
the UVVIS mosaic, the U.S. Geological Survey Integrated Software for Imagers
and Spectrometers (ISIS) processing system [Eliason, 1997; Gaddis et al.,
1997; Torson and Becker, 1997; Anderson et al., 2004] was used to generate
the NIR mosaic. Because the final steps
of the NIR data processing followed the UVVIS processing by several years, the
same version of
Basic cartographic
processing of the NIR mosaic was performed in five stages or "levels". The processing sequence was designed to start
with corrections with highest probability of accuracy to those with the lowest.
The first level of processing, Level 0, ingests
raw data and prepares it for processing by
More information on the
general character of these cartographic processing steps for the NIR data is
provided below. Further details on the
calibration, photometric normalization, and empirical frame-offset correction
required for the NIR mosaics have been described in several publications [e.g., Lucey et al., 1997; Lucey et al.,
1998; Lucey et al., 2000; Eliason et al., 2003; Staid et al., 2003] and are
summarized in the next sections.
Level 0
The Level 0
processing step ingests the raw image data and associated metadata and prepares
them for processing by the
Level 1
The next level of
processing, Level 1, performs radiometric correction and cosmetic enhancement ("clean-up")
on an image. Level 1 consists of a
series of programs to correct or remove image artifacts such as 1) camera
shading inherent in imaging systems, 2) brightness anomalies caused by dust
specks in the optical path, 3) microphonic noise introduced by operation of
other instruments on the spacecraft during image observations, and 4) data
drop-outs and spikes due to missing or bad data from malfunctioning detectors
or missing telemetry data. Level 1
processing results in an "ideal" image that would have been recorded
by a camera system with perfect radiometric properties. In practice, residual artifacts and camera
shading effects remain at a very low level. The density number (DN) values of a
radiometrically corrected image are proportional to the brightness of the
scene. The details for radiometric
correction are described in section 7 below.
Level 2
Production of both
the Clementine UVVIS and NIR mosaics required geometric processing to be
performed on the individual, single-band images. The images are geometrically transformed from
spacecraft camera orientation to a common map coordinate system of a specific
resolution. Before geometric
transformation, images must first be geometrically matched to each other to
establish relative geometric control among the multiband images in a single "color
set" and then the image set must be tied to a ground control net to
establish absolute ground truth. The
process of matching images and tying the image set to ground truth minimizes
the spatial misregistration along image boundaries. The 750-nm basemap provided the geometric
control for the NIR multispectral DIM. This
base map underwent rigorous cartographic processing to tie the imaging to a
lunar geodetic network resulting in an absolute positional accuracy of better
than 0.5 km/pixel for 95% of the surface.
The six NIR spectral bands are coregistered to a precision of 0.2 pixel.
Level 2 geometric
processing also includes correcting camera distortions. This image transformation is based on the
original viewing geometry of the observation (including the optical distortion
model of the camera), relative position of the target, and the mathematical
definition of the map projection. An
additional resampling step is used to perform sub-pixel registration of the 6
bands in the color set. Using the
Level 3
Photometric
normalization is applied to images that make up the NIR DIM to balance
brightness levels among images that were acquired under different lighting
conditions. To illustrate, consider two
images of the same area on the Moon where one image was acquired with the Sun
directly overhead and the second with the Sun lower to the horizon. The image with the higher sun angle would be
significantly brighter than the image with the low sun angle. Photometric normalization causes the two
images to be adjusted to the same brightness level.
Radiometrically
calibrated spacecraft images display the brightness of a scene under specific
angles of illumination, emission, and phase.
Photometric normalization is effective only to the extent that all
geometric parameters can be modeled. For
an object (such as the Moon) without an optically significant atmosphere, this brightness
is controlled by two major influences: 1) the intrinsic properties of the
surface materials, including composition, grain size, roughness, and porosity;
and 2) variations in brightness due to the local topography of the
surface. For both Clementine UVVIS and
NIR photometric processing [e.g., McEwen
et al., 1996; Lucey et al., 1998, 2000; Eliason et al., 2003] the planetary
surface is assumed to be a smooth sphere, so the effects of local topography
are not included in the photometric correction.
However, it is understood that illumination geometry at each pixel
depends on local topography. This means
that the topographic slope within a pixel is not accurately known and
compensated in either the UVVIS or NIR mosaics, so the photometric correction
cannot be perfect. Section 8 describes
the photometric normalization.
Level 4
Compilation of an
accurate digital mosaic of the individual images is the final stage in the
construction of the NIR DIM. The DIM is
created by first generating a blank (or null) image that represents the
regional or global image map of the Moon.
The individual images are then mosaicked into the initially blank image
map. The order in which individual
images are placed into the mosaic is an important consideration. Because images are mosaicked one on top of
the other, images that get laid down first are overwritten in the area of
overlap by subsequent images that are added to the mosaic. Images that have the lowest data quality or
resolution are laid down first, followed by images with highest quality. With this method the areas of image overlap
contain the highest quality images.
Go
to Table of Contents.
7 - RADIOMETRIC CALIBRATION
Radiometric calibration
for the NIR data [Lucey et al., 1987; 1998]
provides correction for camera gain and offset operating modes, pixel dependent
nonuniformity in bias, dark current rate, and responsivity, dark-current
dependence on temperature, removal of thermal background contamination, and
conversion to radiometric units of radiance and/or reflectance. Details of these steps are provided
below. Before radiometric processing
could begin, two calibration issues specific to the NIR data were addressed [Eliason et al., 2003]: 1)
characterization of the instrument operating modes, and 2) characterization of
the instrument thermal background changes during an orbital observation pass
over the Moon.
Instrument
Operating Modes
The goal of this
step was to determine an optimum set of calibration constants to minimize the
difference between calibrated values for portions of the Moon imaged
sequentially with different camera settings [Lucey et al., 2000].
Statistics were acquired for all images collected during systematic
mapping that straddled camera-state boundaries (~19,800 cases). The calibration equation from Lucey et al. [1998] was applied to the entire set of
data, an error function was refined iteratively, calibration constants were
updated, and the process was repeated until little change occurred in the error
function. In this manner the gain,
exposure duration, digital offset, offset multiplier, and global bias were
simultaneously optimized.
Thermal Background
Instrument thermal
background problems were first observed when the initial pre-launch calibration
algorithms were not satisfactorily modeling the NIR deep-space observations
during cool-down tests [Lucey et al.,
1998]. The goal of this step was to
characterize the thermal background changes during an orbital pass and to
define a set of corrections for each orbit.
To characterize these effects, the NIR 1100 nm data were compared to the
highly correlated UVVIS 1000 nm data held as "truth". The UVVIS and NIR images were radiometrically
corrected (with the thermal background remaining in the NIR imaging) and geometrically
coregistered. UVVIS radiance values were
scaled to the NIR data, and the averages of the UVVIS and NIR images in areas
of overlap were computed for all color sets and plotted as a function of the
cryocooler duration. A simple difference
of the NIR and UVVIS bands (NIR/1100 band subtracted by the scaled UVVIS/1000
band) characterizes the change in thermal background in an orbit, and a 3rd
order least-squares fit to the data is a valid model of time-dependent thermal
background for each orbit.
Compensation for the
two effects above was incorporated into the radiometric calibration steps, and
residual effects were removed in later processing. The radiometric calibration process for the
NIR data (performed by the
EQUATIONS
Term1 = (DR(x,y) -
digital_offset ) / Gfact(gm)
Term2 = Term1 -
bias_global - BIAS(x,y) - (om * V)
Term3 = Term2 / t
Term4 = Term3 - global_dc
- DC(x,y)
Iterative for each
background radiance coefficient (ncoef) which is orbit/filter dependent:
background_radiance
= background_radiance +
background_radiance_coefficient(icoef) *
((cryocooler_duration/cryo_norm)
**
(icoef-1))
Term5 = Term4 - background_radiance
- THERMAL(x,y)
R(x,y) = ( (Term5 /
(FF(x,y) * OF(x,y)) ) - AF(x,y) ) *
abscoef
Let:
x,y
= line and sample position of pixel in an image
R(x,y)
= Result of correction in absolute radiance.
DR(x,y) = Raw input density number
FF(x,y) = Flat-field as a function of filter
and line, sample
position. This will be read from an
OF(x,y)
= Orbit dependent flat file correction.
AF(x,y) = Additive component of flat field
correction.
DC(x,y)
= Dark current as a function of compression type,
line, sample position.
BIAS(x,y) = Bias correction as a function of
compression type,
line, sample position.
THERMAL(x,y) = Thermal shade correction based
on thermal shade
file at the north and south
pole.
digital_offset = 8.30690
bias_global
= 2.15547
V
= -0.954194
global_dc
= 0.730
cryo_norm
= 1.0
abscoef
= 1.0
Gfact(gm)= Gain factor as a function of instrument
gain_mode
= 32.0235 (gm=0)
= 28.2755 (gm=1)
= 24.9144 (gm=2)
= 10.9443 (gm=5)
= 24.1835 (gm=8)
= 21.3530 (gm=9)
= 15.9844 (gm=11)
= 7.77177 (gm=13)
= 28.1618 (gm=16)
= 24.8658 (gm=17)
= 21.9100 (gm=18)
= 18.6140 (gm=19)
= 6.83130 (gm=22)
= 3.48425 (gm=23)
= 20.3218 (gm=24)
= 17.9433
(gm=25)
= 15.8104
(gm=26)
= 13.4320 (gm=27)
= 9.32361 (gm=28)
= 6.95951 (gm=29)
= 4.75472 (gm=30)
= 2.43896 (gm=31)
= 13.9238 (gm=33)
= 12.2687 (gm=34)
= 7.23501 (gm=36)
= 7.04438 (gm=41)
= 6.16495 (gm=42)
= 3.57405 (gm=44)
= 2.73995 (gm=45)
= 1.88595 (gm=46)
= 11.9078 (gm=48)
= 9.26433 (gm=50)
= 5.39513 (gm=52)
= 4.08125 (gm=53)
= 1.40899 (gm=61)
= 0.964975
(gm=62)
gm =
Gain_mode of instrument(gm = 0,1,2,5,...,62)
om =
Offset_mode of instrument(om = 1,2,3,4,...,31)
t =
Optimal integration duration of observation in
seconds (A function of
EXPOSURE_DURATION on labels
in milliseconds.)
PROGRAM STRATEGY
NIRCAL reads the
keyword label area from the input file to obtain processing parameters to
radiometrically correct the image. The
following keywords are extracted from the keyword label area:
TABLE OF IMAGE
KEYWORDS USED BY NIRCAL
--------------------------------------
INSTRUMENT_ID -
Camera (Should be NIR)
GAIN_MODE_ID -
Instrument gain mode
OFFSET_MODE_ID -
Instrument offset mode
CRYOCOOLER_DURATION -
Cryocooler duration
EXPOSURE_DURATION -
Exposure time of camera
BAND_BIN_FILTER_NAME - Instrument filter name
(A,B,C,D,E,F) for (1100, 1250,
1500, 2000, 2600,
2780 nm,
respectively)
After obtaining the
image keywords from the image label area and determining all processing
parameters, NIRCAL opens the appropriate calibration files and processes the
image.
Go
to Table of Contents.
8 - PHOTOMETRIC FUNCTION NORMALIZATION
The Clementine data
have large changes in brightness because they were acquired under a broad range
of viewing conditions, with phase, emission, and incidence angles varying from
0 to 90 degrees. To create NIR mosaics
with uniform scene brightness, a photometric normalization procedure was
applied [McEwen, 1996; McEwen et al., 1998] to the individual images
before compiling the global mosaic. The
data are normalized to R30, the
reflectance expected at an incidence angle (i) and phase angle (p) of 30.0
degrees and an emission angle (e) of 0.0 degrees matching the photometric
geometry of lunar samples measured at the reflectance laboratory at Brown
University [Pieters et al., 1991].
Differences in phase behavior, especially near 0.0 degrees, as a
function of terrain type were observed in the resulting mosaics. A second-order correction to the phase
function for near zero phase observations was developed and applied to the
data. This procedure compared areas of
overlap among low and high-phase imaging for determining a multiplicative
correction to the low-phase imaging which forced overlapping areas to match. The resulting multiplicative corrections were
then applied to the low-phase imaging in non-overlap areas.
The modified
Lunar-Lambert function used in the processing [McEwen, 1996; McEwen et al., 1998] is as follows:
XL(i,e,p) = 2*L(p)*u0/(u+u0) + (1-L(p))*u0
where:
i = incidence angle
e = emission angle
p = phase angle
u = cos(e)
u0 = cos(i)
L = variation of the limb-darkening
parameter expressed
as a third-order polynomial:
L(p)
= 1.0 + A*p + B*(p**2) + C*(p**3)
A = -0.019
B =
0.242E-3
C = -1.46E-6
The phase function
correction based on work from Helfenstein is defined as follows:
F(p) = B(p,h,b0)*[(1-f)*P(p,g1) + f*P(p,g2)]
B(p,h,b0) = 1 + b0/(1+tan(p/2)/h) (Backscatter
function)
P(p,g) = (1-g**2)/(1+g**2+2*g*cos(p)**1.5)
b0 = wave length dependent
constant (see table below)
The g1 parameter is expected to vary with
albedo, modeled as:
g1 = d*R30 + e (however, d=0 for Clementine processing, thus eliminating
any correction for albedo).
R30 = normalized albedo
To describe the
backscatter function at less than 2 degrees phase angle, the following linear
functions are used based on results from Burratii [McEwen, 1996]:
F(p)
= 1.0 + xb
xb = xb0 + xb1 * wave_length
where:
xb0 = -0.0817
xb1 = 0.0081
Final normalization
to the RELAB geometry is given by:
R30 = R(i,e,p)*[XL(30,0,30)/XL(i,e,p)]*[F(30)/F(p)]
where: f,g2,b0,h are parameters determined by
fits to a dataset.
Values applied to
the Clementine NIR data were derived for the UVVIS E filter (1000 nm) and these
have been applied to all six NIR wavelengths.
Note that d=0 means that
we do not attempt to vary the photometric correction as a function of albedo.
Filter b0 h d
e f g2
--------------------------------------------------
NUA (1100 nm)
1.35 0.052 0 -0.226 0.5 0.36
Go
to Table of Contents.
9 - EMPIRICAL FRAME
OFFSET CORRECTIONS
Processing of the NIR
data based on the radiometric and photometric procedures described above
resulted in global mosaics, which had achieved a "standard" level of
processing and calibration. Examples of
these data have been released on the USGS Clementine NIR data Web site: http://astrogeology.usgs.gov/Projects/ClementineNIR/
.In addition to this standard radiometric and photometric processing,
empirically derived frame offset corrections were applied to produce a second
version of the mosaics with reduced variability across camera modes and
adjacent orbits [Staid et al., 2003]. This additional processing resulted in "frame
offset corrected" mosaics extending from 70 degrees N to 70 degrees S and
is described in more detail below. Note
that polar regions above 70 degrees were not included in this additional
processing (see also page 22).
Frame Offset
Corrections
After radiometric
and photometric calibrations were applied to the NIR data [e.g., Eliason et al., 2003], additional corrections were derived to
adjust for remaining problems in the characterization of specific camera modes
and the drift of radiometric properties over the two month Clementine
observation period. Problems in the
existing NIR calibrations (standard processing version) were apparent in both
NIR albedo images and ratio images of NIR and NIR to UVVIS bands. Though such problem areas were typically
associated with ten degree latitude strips where specific camera settings were
poorly characterized, no systematic correction for these residual errors was
apparent based on comparisons of image means with gain and offset camera mode
values. As a result, a set of empirical
corrections was developed to reduce within- and between-orbit variations for
each NIR band as described below.
To identify
Clementine NIR frames with residual calibration errors, ratio images were
created by dividing each radiometrically and photometrically calibrated NIR
band to the USGS calibrated 750 nm UVVIS data.
To make computational processing more efficient, the NIR data were
divided by longitude into twelve 30-degree wide strips at a resolution of 1
km/pixel. Several thousand "truth"
image frames were then selected for each NIR band of each strip based on orbits
and camera mode states that demonstrated the least amount of radiometric
variability across NIR/UVVIS ratio images.
Image frames that were not included in the selected truth sets were then
adjusted by computing an offset for each frame based on color ratio differences
in overlapping regions of the frame being corrected and the surrounding
truth-set frames. This procedure was
applied to each longitude strip to derive a global set of offset frame
corrections for each NIR band.
Derived frame offset
corrections for each NIR band were then applied to a global mosaic of
Clementine NIR data at 2 km/pixel resolution.
New ratio images of the NIR channels over the UVVIS 750 nm data were
created from the frame offset-corrected NIR data to evaluate results. Uniformity across camera mode settings and
orbits was improved in the resulting ratio images for most regions. Offset correction values for NIR frames that
had not been improved by the automated offset correction algorithm due to
within-image gradients or lack of adequate surrounding truth images were either
eliminated from the offset corrections or adjusted manually based on visually
matching values with surrounding frames in the ratio images.
After applying the
best set of frame offset corrections derived through the above steps, a final
small offset correction was then computed for every image frame in the
Clementine global mosaic to correct for residual between-orbit variations. This was carried out by differencing the
global ratio of each NIR band over the 750 nm band by the same data after
applying a longitudinal median filter.
The width of the longitudinal median filter was varied until a filter
was identified that captured albedo offsets across orbits while minimizing the
influence of geologic albedo and color boundaries on the subsequently derived
offset corrections. The mean difference
of the pre- and post-filter ratio images was derived for all six bands of each
Clementine frame, smoothed as a function of latitude within each orbit and
added to the previous offset correction values.
The final result of
the offset deviation processing described above was a single text file
containing an offset correction by NIR band for every frame in the Clementine
mosaic (see nir_mosaic_frameoffset.txt).
A file containing the corresponding area of Clementine frames is
included along with the 0.5 km NIR mosaics available online at http://astrogeology.usgs.gov/Projects/ClementineNIR/
. These offset values were then
subtracted from the radiometrically corrected NIR data to create the
offset-corrected, full-resolution (100 m/pixel) mosaics.
A final
multiplicative correction equivalent to the month1-to-month2 correction applied
to the calibrated global UVVIS data was also applied to the offset corrected
NIR mosaic (frame-based NIR calibrations were made relative to the 750 nm UVVIS
data before this final multiplicative correction had been applied.) Orbit-to-orbit
multiplicative corrections as a function of Clementine frame color-set number
are included in nir_mosaic_framemult.txt available at this Web site: http://astrogeology.usgs.gov/Projects/ClementineNIR/
.
Apollo 16
Normalization
Apollo 16 soil
measurements previously used to normalize and calibrate the UVVIS data [Pieters et al., 1999] to units of
reflectance were convolved through the first four NIR filter transmission
curves. Values obtained from the soil
spectra were then compared with DN values from the NIR data of the same Apollo
16 landing site location used to calibrate the UVVIS data. Multiplicative ‘reflectance normalization’
correction factors were derived for the first four bands of the NIR data (1100
- 2000 nm), and the data from NIR these bands were calibrated to reflectance. Multiplicative correction factors derived
from the ‘standard’ data and the offset-corrected NIR data were consistent to ~2%
or better for all four bands. Due to a
decrease in orbit-to-orbit variability around the Apollo 16 landing site used
for normalizations, correction values derived from the final offset-corrected
mosaics were used for the final normalizations and are presented in the table
below. The longest NIR wavelengths (2600
and 2780 nm bands) were not normalized to these soil measurements because
reflectance information was not available at these wavelengths and their brightness’s
may have been complicated by the additional presence of thermal emission
signatures.
Apollo
16 Coefficients for Calibration to Reflectance
NIR
Band Coefficient
1100
nm 0.127860
1250
nm 0.116715
1500
nm 0.158662
2000
nm 0.295333
The processing steps
described above for the NIR mosaics were applied to data from 70 degrees N to 70
degrees S only. The polar regions were
processed through 'standard' processing steps only, and the later empirical
frame offset and multiplicative corrections were not applied. This was due to multiple overlapping frame
coverage and the difficulty in selecting optimal image coverage and deriving a
single representative offset correction value for a given frame to be
corrected.
Sources of Error
These global Clementine
NIR mosaics represent a large improvement in radiometric calibrations over the
original mission calibrations [Lucey et
al., 1998, 2000]. More recent work
illustrates the utility of these NIR mosaics [Cahill et al., 2004; Staid et al., 2004; Gillis et al., 2005]. However, residual errors remain and these
influence usage of the data. The
presence and approximate magnitudes of such errors can be identified in ratio
images of various bands of the global NIR data where color variations change
across orbits and camera modes that cannot be attributed to surface materials. Though such color variations are less
apparent in the frame corrected version of the NIR data, some residual patterns
due to imperfect calibrations are known to exist in this latter version of the
data as well. As a result, it may be
useful to compare both sets of global data when conducting regional-scale
analyses to identify local variations introduced by imperfect radiometric
calibrations and empirical corrections.
Due to the potential for such local variations in radiometric
calibrations, it is advantageous to conduct spectral analyses of the data over
relatively large regions that include several different orbits and camera
modes.
Possible sources of
error in the Clementine NIR data include variations in photometric properties
of materials within a scene, stray and/or scattered light and unknown and uncorrected phase and
photometric effects for NIR wavelengths.
Scattered light is possible anomalous brightness in which high-albedo
units influence the measured values of low-albedo units (and vice versa) to
varying degrees at different wavelengths.
There is good evidence that the NIR camera suffered from stray light
effects, but to a lesser and qualitatively
different degree than the UVVIS camera [e.g., Lucey et al., 1998]. Other sources of error include the assumption
that the Apollo 16 sample measurements are representative of (1) the larger
lunar surface region used for normalization to reflectance, and (2) other lunar
terrain types such as maria. Cahill et al.
[2004] note that the noise levels in
the corrected NIR data are near 1% (compared to ~0.5% for the UVVIS calibrated
data) and that comparisons between Earth-based spectra and those derived from a
dozen sites on the nearside generally correspond to within 1-sigma standard
deviation.
Go
to Table of Contents.
10 - CONVERSION
OF 16-BIT PIXEL VALUES TO FLOATING POINT NUMBERS
To convert the
16-bit integer values found in the image arrays of the NIR multispectral mosaic
to radiance and/or fractional reflectance an
offset and scaling factor need to be applied as shown:
FRACTIONAL_REFLECTANCE = (SCALING_FACTOR * DN) + OFFSET
where: DN = 16-bit pixel value of NIR DIM
image array.
SCALING_FACTOR = 1.3500E-04
OFFSET = 0.00
The
Go
to Table of Contents.
11 - FILES, DIRECTORIES, AND DISK CONTENTS
The files on each CD
volume are organized starting at the root or 'parent' directory. Below the
parent directory is a directory tree containing data, documentation, and index
files. In the table below directory names are indicated by brackets
(<...>), upper-case letters indicate an actual directory or file name,
and lower-case letters indicate the general form of a set of directory or file
names.
DIRECTORY/FILE
CONTENTS
<root>
|
|-AAREADME.TXT Introduction to the CD volume (ASCII
Text)
|
|-INDEX.HTM Hypertext Markup Language (HTML)
file for use
| as a user-interface to
files on this volume.
|
|-ERRATA.TXT Description of known anomalies and
errors
| present on the volume
set (optional file).
|
|-VOLDESC.CAT A description of the contents of
this
| CD volume in a format
readable by
| both humans and
computers.
|
|-<CATALOG> Catalog Directory
| |
| |-CATINFO.TXT Describes Contents of the Catalog
directory
| |
| |-DATASET.CAT Clementine NIR DIM Mosaic description
| |
| |-DSMAP.CAT Map Projection description
| |
| |-INSTHOST.CAT Clementine Spacecraft description
| |
| |-MISSION.CAT Clementine Mission description
| |
| |-PERSON.CAT Contributors to Clementine NIR Mosaic
| |
| |-REF.CAT References for Clementine NIR
Mosaic
| |
| |-NIRINST.CAT NIR
Camera description
|
|-<DOCUMENT> Documentation Directory. The files
in this
| | directory provide detailed
information
| | regarding the Clementine NIR
Mosaic.
| |
| |-DOCINFO.TXT Description of files in the DOCUMENT
| | directory.
| |
| |-VOLINFO.TXT Documentation regarding the
| | contents of this CD Volume.
| |
| |-VOLINFO.HTM HTML document for VOLINFO.TXT
| |
| |-VOLINFO.LBL PDS Label file describing the VOLINFO
| | documents.
| |
| |-SCHEME.PDF Adobe Acrobat Portable Document Format
file
| showing NIR tiling and
volume scheme.
|
|-<INDEX> Directory for the image index
files.
| |
| |-INDXINFO.TXT Description of files in <INDEX>
directory.
| |
| |-INDEX.TAB Image Index table specific to each
volume.
| |
| |-INDEX.LBL PDS label for INDEX.TAB
| |
| |-CUMINDEX.TAB Image Index table for entire CD
collection.
| |
| |-CUMINDEX.LBL PDS label for CUMINDEX.TAB.
|
|-<DATA> Data directory containing NIR
DIM tiles.
| |
| |-<tsppymmm.xxx> Data filenames where;
| (For this NIR
Volume Set)
| t = N (Clementine NIR Mosaic)
|
| (For past or
future Volumes)
| = B (Clementine
Basemap Mosaic)
| = U (UVVIS Cube)
| = N (NIR Cube)
| = L (LWIR Image
Data)
| = H (Hi-res Image
Data)
|
| s = (Resolution -
km/pixel)
| = A (0.004 km/pixel - future mapping)
| = B-D (For future
mapping as needed)
| = E (0.02 km/pixel - future mapping)
| = F-H (For future
mapping as needed)
| = I (0.1 km/pixel)
| = J (0.15 km/pixel)
| = K-L (For future
mapping as needed)
| = M (0.5 km/pixel)
| = N-P (For future
mapping as needed)
| = Q (2.5 km/pixel)
| = R-T (For future mapping as needed)
| = U (12.5 km/pixel)
| = V-Z (For future
mapping as needed)
|
| pp = (00-90) Center
latitude of Image File.
| (Two digit truncated integer)
|
| y = N (Positive
latitude)
| = S (Negative
latitude)
| = <none>
(Not used for full latitude
| coverage. i.e. -90 to 90)
|
| mmm = (000-360) Center
longitude of Image.
| (Three digit
truncated integer)
| xxx = IMG (PDS Labeled
Image File)
| = LAB (
| = JPG (JPEG small,
medium, and
| large Browse
Images) <BROWSE>
| Directory Tree
only
| = HTM
(<BROWSE> Directory Tree only)
|
|
|-<BROWSE> Directory tree containing
enhanced color,
| color ratio, and b/w
(2000nm) “Browse”
| (reduced resolution) JPEG
images for each
| image data product on the volume.
|
|-BROWINFO.TXT Description of <BROWSE> content.
|
|-BRCOLOR.HTM Graphics (map)-based HTML interface to
| enhanced color browse data
| (Accessed by INDEX.HTM
file).
|
|-BRRATIO.HTM Graphics (map)-based HTML interface to
| color ratio browse data
| (Accessed by INDEX.HTM
file).
|
|-BRBW.HTM Graphics (map)-based HTML interface
to
| b/w (2000
nm) browse data
| (Accessed by INDEX.HTM
file).
|
|-LOCATOR.HTM Volume/Quad Locator Map.
|
|-CLEMLOGO.GIF Various icons, logos, and images
|-USGSLOGO.GIF used by HTML documents on the volume.
|-CLEMGRID.GIF
|-GR17.GIF
|-GR38.GIF
|
|
|-<COLOR>
|
|-<SMALL>
|
|-<MEDIUM> Directory
tree containing small, medium,
|
|-<LARGE> and large
sized JPEG images (enhanced color,
| color ratio, and b/w (2000nm))
for each
|-<RATIO> DIM product. These JPEG images are
primarily
|
|-<SMALL> used by
the HTML documents on the volume.
|
|-<MEDIUM> small
images are ~60x60 pixels
|
|-<LARGE> medium
images are ~400x400 pixels
| large images are ~1000x1000
pixels
|-<2000nm>
|-<SMALL>
|-<MEDIUM>
|-<LARGE>
Go
to Table of Contents.
12 - IMAGE FILE ORGANIZATION
The image files are
stored in a PDS compliant format. An image file contains a label area (header)
at the beginning of the file followed by the image data. The number of bytes of
the label area is a multiple of the number of bytes that make up an image line
(number of samples * 2 bytes/pixel). The image label area contains ASCII text
data that describing the image file (see Image Labels section below). The label
area can be viewed with a simple ASCII editor on most computer systems.
ISIS access to NIR
DIM
Each NIR image file
(*.img filename extension) is associated with an Integrated Software for
Imagers and Spectrometers (ISIS) 'qube object' detached label (.lab filename
extension). This detached label allows for images to be accessed and processed
within the ISIS system (available through the USGS,
Pixel Storage
Order
The Clementine NIR
mosaic is stored as image files with 16-bit signed integer pixels. The storage
order of the pixels is "most significant byte order first." This is
the storage order for Unix/Sun and Macintosh systems. For other systems such as
IBM-compatible PC, Dec/Alpha, and VAX systems, the high and low order bytes of
the pixels will need to be swapped before the data can be used. The
Special Pixel
Values
Pixels in an image
array can contain special values to denote a special condition about a pixel.
The following values designate a special pixel:
-32768 - NULL - The
pixel is "empty" and no data were acquired for this pixel location in
the image array. This condition typically occurs when a gap exists in the image
map such as when an image was not acquired for an area of the Moon.
-32767 - Low
Processing Saturation - Processing on the pixel caused its value to go outside
the low-end dynamic range of the 16-bit signed integer.
-32766 - Low
Instrument Saturation - The pixel of the raw image was "bit clipped"
and did not contain a valid value. For example, if the bias of the camera was
set so that the low DN values could not be stored in the dynamic range of the
raw image.
-32765 - High
Instrument Saturation - The pixel of the raw image was high-end saturated and
could not be stored in the dynamic range of the raw image. For example, if part
of an image scene was too bright to be recorded by the imaging instrument.
-32764 - High
Processing Saturation - Processing on the pixel caused its value to go outside
the high-end dynamic range of the 16-bit signed integer.
Image Labels
The label area of an
image file contains descriptive information about the image. The label consists
of keyword statements that conform to version 3 of the Object Description
Language (ODL) developed by NASA's PDS project. There are three types of ODL
statements within a label: structural statements, keyword assignment
statements, and pointer statements.
Structural
statements provide a shell around keyword assignment statements to delineate
which data object the assignment statements are describing. The structural
statements are:
1) OBJECT =
object_name
2) END_OBJECT
3) END
The OBJECT statement
begins the description of a particular data object and the END_OBJECT statement
signals the end of the object's description. All keyword assignment statements
between an OBJECT and its corresponding END_OBJECT statement describe the
particular object named in the OBJECT statement. The END statement terminates a
label. A keyword assignment statement contains the name of an attribute and the
value of that attribute. Keyword assignment statements are described in more
detail in Appendix A of this document. These statements have the following
format:
name = value
Values of keyword
assignment statements can be numeric values, literals, and text strings.
Pointer statements
are a special class of keyword assignment statements. These pointers are
expressed in the ODL using the following notation:
^object_name =
location
If the object is in
the same file as the label, the location of the object is given as an integer
representing the starting record number of the object, measured from the
beginning of the file. The first label record in a file is record 1. Pointers
are useful for describing the location of individual components of a data
object. Pointer statements are also used for pointing to data or label
information stored in separate files. An example of a detached label (i.e.,
label information stored in a separate file) is shown below: By convention,
detached labels are found in the LABEL directory.
^STRUCTURE =
'logical_file_name'
The value of 'logical_file_name'
is the name of the detached label file containing the description.
The keyword
statements in the label are packed into the fixed-length records that make up
the keyword label area. Each keyword statement is terminated by a carriage-return
and line-feed character sequence. An example of a Clementine NIR DIM image
label is shown below. Descriptions of the keywords used in the NIR label are
found in Appendix A.
Example PDS
Label for Clementine NIR DIM Image files
PDS_VERSION_ID = PDS3
/* FILE FORMAT AND LENGTH */
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 3688
FILE_RECORDS = 10637
LABEL_RECORDS = 2
INTERCHANGE_FORMAT = BINARY
/* POINTERS TO START RECORDS OF OBJECTS IN
FILE */
^IMAGE = 3
/* IMAGE DESCRIPTION */
DATA_SET_ID = "CLEM1-L-N-5-DIM-NIR-V1.0"
PRODUCT_ID = "NI03N003"
PRODUCER_INSTITUTION_NAME
= "UNITED STATES GEOLOGICAL
SURVEY"
PRODUCT_TYPE = MDIM
MISSION_NAME = "DEEP SPACE PROGRAM
SCIENCE
EXPERIMENT"
SPACECRAFT_NAME = "CLEMENTINE 1"
INSTRUMENT_NAME = "NEAR INFRARED CAMERA"
INSTRUMENT_ID = "NIR"
TARGET_NAME = "MOON"
FILTER_NAME =
("A","B","C","D","E","F")
CENTER_FILTER_WAVELENGTH = (1110.000,1250.000,1500.000,
2000.000,2600.000,2780.00)
BANDWIDTH = (60.000,60.000,60.000,
60.000,60.000,120.000)
START_TIME = "N/A"
STOP_TIME = "N/A"
SPACECRAFT_CLOCK_START_COUNT = "N/A"
SPACECRAFT_CLOCK_STOP_COUNT = "N/A"
PRODUCT_CREATION_TIME = 2006-05-25T13:30:03
NOTE = "NIR 6-BAND
MOSAIC"
/* DESCRIPTION OF OBJECTS CONTAINED IN
FILE */
OBJECT = IMAGE
BANDS = 6
BAND_STORAGE_TYPE = BAND_SEQUENTIAL
BAND_NAME = "N/A"
LINES = 2127
LINE_SAMPLES = 1844
SAMPLE_TYPE = MSB_INTEGER
SAMPLE_BITS = 16
SAMPLE_BIT_MASK = 2#1111111111111111#
OFFSET = 0.0
SCALING_FACTOR = 1.350000E-04
VALID_MINIMUM = -32752
NULL = -32768
LOW_REPR_SATURATION = -32767
LOW_INSTR_SATURATION = -32766
HIGH_INSTR_SATURATION = -32765
HIGH_REPR_SATURATION = -32764
MINIMUM = 878
MAXIMUM = 11120
CHECKSUM = 3245986915
END_OBJECT = IMAGE
OBJECT = IMAGE_MAP_PROJECTION
^DATA_SET_MAP_PROJECTION = "DSMAP.CAT"
COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING"
COORDINATE_SYSTEM_NAME = "PLANETOGRAPHIC"
MAP_PROJECTION_TYPE = "SINUSOIDAL"
MAP_RESOLUTION = 303.2334900
MAP_SCALE = 0.1000000
MAXIMUM_LATITUDE = 7.0000000
MINIMUM_LATITUDE = -0.0132000
EASTERNMOST_LONGITUDE = 6.0131998
WESTERNMOST_LONGITUDE = 0.0000000
LINE_PROJECTION_OFFSET = 2123.6345297
SAMPLE_PROJECTION_OFFSET = 4549.5024429
A_AXIS_RADIUS = 1737.4000000
B_AXIS_RADIUS = 1737.4000000
C_AXIS_RADIUS = 1737.4000000
FIRST_STANDARD_PARALLEL = "N/A"
SECOND_STANDARD_PARALLEL = "N/A"
POSITIVE_LONGITUDE_DIRECTION = EAST
CENTER_LATITUDE = 0.0
CENTER_LONGITUDE = 15.0000000
REFERENCE_LATITUDE = "N/A"
REFERENCE_LONGITUDE = "N/A"
LINE_FIRST_PIXEL = 1
SAMPLE_FIRST_PIXEL = 1
LINE_LAST_PIXEL = 2127
SAMPLE_LAST_PIXEL = 1844
MAP_PROJECTION_ROTATION = 0.0000000
VERTICAL_FRAMELET_OFFSET = "N/A"
HORIZONTAL_FRAMELET_OFFSET = "N/A"
END_OBJECT = IMAGE_MAP_PROJECTION
END
Go
to Table of Contents.
13 - INDEX FILES
Each CD volume in
the Clementine NIR mosaic contains an image index table ('index.tab')
with catalog information specific to each volume. A cumulative index table ('cumindex.tab')
is also provided. It contains entries for the entire NIR DVD collection. The
image index files and their associated PDS label files ('index.lbl' and 'cumindex.lbl')
are located in the 'index' directory. The index table includes the file
names, CD volumes, and mapping parameter information.
Go
to Table of Contents.
14 - ACKNOWLEDGMENTS
The National
Aeronautics and Space Administration is charged with the responsibility for
coordination of a program of systematic exploration of the planets by
The Clementine NIR
DIM was compiled for the National Aeronautics and Space Administration (NASA)
by the United States Geological Survey (USGS) under the direction of Lisa
Gaddis (USGS) and Eric M. Eliason (USGS, now at The University of Arizona). Paul Lucey, Donovan Steutel, Dave Blewett, and
John Hinrichs (the latter two are now at NovaSol,
Generation of the NIR
DIM is a very complex process that involves and depends on an extended number
of people. In Completion of this product is the result of contributions by the
following individuals and groups in Astrogeology at USGS/Flagstaff:
Data Processing: Ella
Mae Lee, Lynn Weller, Bob Sucharski, Janet Richie, Ana Grecu, Alicyn Gitlin
Data Review: Ella
Mae Lee, Lynn Weller, Annie Bennett
Scripting: Eric Eliason, Ella Mae
Lee, Lynn Weller, Tammy Becker, Tracie Sucharski, John Shinaman, and Bob
Sucharski
Database: Janet Barrett, Ella Mae
Lee, Bob Sucharski
Data Management: Annie Bennett, Lynn Weller
A variety of developers
and programmers within the
Go
to Table of Contents.
15 - REFERENCES
Anderson, J.A., S.C.
Sides, D.L. Soltesz, T.L. Sucharski, K.J. Becker, Modernization of the Integrated Software for Imagers and Spectrometers,
Lunar and Planetary Science Conference XXXV, abstract #2039, 2004.
Batson, R.M., Cartography: in Greeley, Ronald, and Batson, eds. Planetary
Mapping:
Batson, R.M., Digital
Cartography of the Planets: New Methods, Its Status, and Its Future: Photogrammetric
Engineering and Remote Sensing, Vol. 53, No. 9, p.1211-1281, 1987.
Cahill, J.T., P.G.
Lucey, J.J. Gillis, D. Steutel, Verification
of quality and compatibility for the newly calibrated Clementine NIR Data Set,
Lunar and Planetary Science Conference XXXV, abstract #1469, 2004.
Cook, A.C., B. Semenov, M.S. Robinson, and
T.R. Watters, Assessing the Absolute
Positional Accuracy of the Clementine UVVIS Mosaic, Proceedings of the 36th
Vernadsky-Brown Microsymposium,
Eliason, E.M., Production
of Digital Image Models Using the
Eliason, E., C.
Isbell, E. Lee, T. Becker, L. Gaddis, A. McEwen, M. Robinson, Mission to the Moon: The Clementine UVVIS
Global Lunar Mosaic, PDS Volumes USA_NASA_PDS_CL_4001 through 4078,
produced by the U.S. Geological Survey and distributed on CD media by the
Planetary Data System, 1999.
Eliason, E.M., E.M.
Lee, T.L. Becker, L.A. Weller, C.E. Isbell, M.I. Staid, L.R. Gaddis, A.S.
McEwen, M.S. Robinson, T. Duxbury, D. Steutel, D.T. Blewett, and P.G. Lucey, A Near-Infrared (NIR) global multispectral
map of the Moon from Clementine, Lunar and Planetary Science Conference
XXXIV, abstract #2093, 2003.
Eliason, E.M., E.R.
Malaret, and G. Woodward, Clementine Mission, The Archive of Image Data
Products and Data Processing Capabilities: Lunar and Planetary Science
Conference 26th, pp. 369-370, 1995.
Eliason, E.M., A.S.
McEwen, M.S. Robinson, E.M. Lee, T.L. Becker, L. Gaddis, L.A. Weller, C.E.
Isbell, J.R. Shinaman, T. Duxbury, E. Malaret, Clementine: A Global
Multi-Spectral Map of the Moon from the Clementine UVVIS Imaging Instrument:
Lunar and Planetary Science Conference 30th, pp. 1933-1934, 1999.
Eliason, E., A.
McEwen, M. Robinson, P. Lucey, T. Duxbury, E. Malaret, C. Pieters, T. Becker,
C. Isbell, E. Lee, Multispectral Mapping
of the Moon by Clementine, New Views of the Moon 1998, abstract #6006,
1998.
Gaddis, L.R.,
Anderson, J., Becker, K., Becker, T., Cook, D., Edwards, K., Eliason, E., Hare,
T., Kieffer, H., Lee, E.M., Mathews, J., Soderblom, L., Sucharski, T., and
Torson, J., An overview of the
Integrated Software for Imaging Spectrometers (ISIS), Lunar and
Planetary Science Conference XVIII,
387-388, 1997.
Gillis, J.J., P.G.
Lucey, B.A. Campbell, and B.R. Hawke, Clementine
2.7 micron data and 70-cm Earth-based radar data provide additional constraints
for UVVIS-based estimates of TiO2 content for lunar mare basalts, Lunar
and Planetary Science Conference XXVI,
abstract #2254, 2005.
Isbell, C.E., E.M.
Eliason, K.C. Adams, T.L. Becker, A.L. Bennett, E.M. Lee, A.S. McEwen, M.S.
Robinson, J.R. Shinaman, and L.A. Weller, Clementine: A Multi-Spectral
Digital Image Model Archive of the Moon: Lunar and Planetary
Science Conference 30th, pp. 1812-1813, 1999.
Isbell, C.E., E.M.
Eliason, E.M. Lee, K.C. Adams, T.L. Becker, A.L. Bennett, A.S. McEwen, Clementine:
Reduced Resolution Digital Image Model of the Moon: Lunar and
Planetary Science Conference 32nd, abstract #2076, 2001.
Jet Propulsion
Laboratory, Planetary Data System Standards Reference: JPL Document
D-7669, Part 2, Jet Propulsion Laboratory,
Lawson, S.L., B.M.
Jakosky, H.-S. Park, and M.T. Mellon, Brightness
temperatures of the lunar surface: Calibration and global analysis of the
Clementine long-wave infrared camera data, J. Geophys. Res., 105, No. E2, 4273-4290, 2000.
Lee, E.M., K.E.
Edwards, T.L. Becker, D. Cook, E. Eliason, M.S. Robinson, A.S. McEwen, T.
Colvin, M. Davies, T. Duxbury, T. Sorenson, 1997, Clementine UVVIS Multispectral Processing, Lunar and Planetary
Science Conference XXVIII,
abstract #1705, 1997.
Le Mouelic, S., Y.
Langevin, and S. Erard, A new data
reduction approach for the Clementine NIR data set: Application to Aristillus, Aristarchus, and
Kepler, Journal of Geophysical Research, v. 104, No. E2, pp. 3833-3843,
1999.
Lewis,
Li, Lin, J.F.
Mustard, and C.M. Pieters, The Effects of Scattered Light in the Clementine
UVVIS Camera on Mixture Analysis, Lunar and Planetary Science Conference
30th, pp. 1356-1357, 1999.
Lucey, P.G., J.L.
Hinrichs, and
Lucey, P.G., J.
Hinrichs, C. Budney, G. Smith, C. Frost, B.R. Hawke, E. Malaret, M.S. Robinson,
B. Bussey, T. Duxbury, D. Cook, P. Coffin, E. Eliason, T. Sucharski, A. McEwen,
C.M. Pieters, Calibration of the Clementine
Near Infrared Camera: Ready for Prime
Time, Lunar and Planetary Science Conference XXXI, Abstract #1576, 1998.
Lucey, P.G., D.T.
Blewett, E. Eliason, L.A. Weller, R. Sucharski, E. Malaret, J.L. Hinrichs, and
P.D. Owensby, Optimized calibration
constants for the Clementine NIR camera, Lunar and Planetary Science
Conference XXIX, #1273, 2000.
McEwen, A.S., E.
Eliason, P. Lucey, E. Malaret, C. Pieters, M. Robinson, T. Sucharski, Summary
of Radiometric Calibration and Photometric Normalization Steps for the
Clementine UVVIS Images: Lunar and Planetary Science Conference 29th,
pp. 1466-1467, 1998.
McEwen, A.S., M.
Robinson, Mapping of the Moon by Clementine: Adv. Space Research,
Vol. 19, No. 10, pp. 1523-1533, 1997.
McEwen, A.S., A
Precise Lunar Photometric Function: Lunar and Planetary Science
Conference 27th, pp. 841-842, 1996.
Nozette, S., P.
Rustan, L.P. Pleasance, D.M. Horan, P. Regeon, E.M. Shoemaker, P.D. Spudis,
C.H. Acton, D.N. Baker, J.E. Blamont, B.J. Buratti, M.P. Corson, M.E. Davies, T.C.
Duxbury, E.M. Eliason, B.M. Jakosky, J.F. Kordas, I.T. Lewis, C.L. Lichtenberg,
P.G. Lucey, E. Malaret, M.A. Massie, J.H. Resnick, C.J. Rollins, H.S. Park,
A.S. McEwen, R.E. Priest, C.M. Pieters, R.A. Reisse, M.S. Robinson, D.E. Smith,
T.C. Sorenson, R.W. Vorder Breugge, and M.T. Zuber, The Clementine Mission
to the Moon: Scientific Overview: Science, Vol. 266, pp. 1835-1839,
1994.
Pieters, C., Compositional diversity and stratigraphy of
the lunar crust derived from reflectance spectroscopy, Chap. 14 in Remote
Geochemical Analysis: Elemental and Mineralogical Composition, C. Pieters and
P. Englert (ed.),
Pieters, C.M., The Moon as a Spectral Calibration Standard
Enabled by Lunar Samples: The Clementine
Example, in New Views of the Moon II: Understanding the Moon Through the
Integration of Diverse Datasets, September 22-24, 1999, Flagstaff, Arizona,
abstract 8025 (http://www.planetary.brown.edu/pds/Pieters_NV99_8025.pdf),
1999.
Pieters, C.M., S.
Pratt, H. Hoffmann, P. Helfenstein, and J. Mustard, Bi-directional
Spectroscopy of Returned Lunar Soils: Detailed "Ground Truth" for
Planetary Remote Sensors: Lunar and Planetary Science Conference 22nd,
pp. 1069-1070, 1991.
Priest, R.E., I.T. Lewis, N.R. Sewall, H. Park, M.J. Shannon, A.G. Ledebuhr, L.D. Pleasance, M.A. Massie, and K. Metschuleit, Near-infrared Camera for the Clementine Mission, Proceedings of the Society of Photo-optical Instrumentation Engineers (SPIE), 2475, pp. 393-404, 1995.
Robinson, M.S., A.S.
McEwen, E.M. Eliason, E.M. Lee, E. Malaret, P. Lucey, Clementine UVVIS
Global Mosaic: A New Tool for Understanding the Lunar Crust: Lunar and
Planetary Science Conference 30th, pp. 1931-1932, 1999.
Robinson, M.S.,
Snyder, J.P, Map
Projections - A Working Manual:
Staid, M.I., C.
Isbell, L. Gaddis, E. Eliason, E.M. Lee, T. Becker, L. Weller, J. Shinaman, D.
Steutel, P. Lucey, J. Gillis, A. McEwen, M. Robinson, T. Duxbury, E. Malaret,
B. Jolliff, C. Pieters, Clementine
Near-Infrared Global Multispectral Map, First Release, Online document and images (http://astrogeology.usgs.gov/Projects/ClementineNIR/),
2003.
Staid, M.I., L.R.
Gaddis, C.E. Isbell, Global comparisons of mare volcanism from Clementine NIR
data, Lunar and Planetary Science Conference XXXV, abstract #1925, 2004.
Torson, J.M. and
K.J. Becker,
Go
to Table of Contents.
APPENDIX A - KEYWORD ASSIGNMENTS
This section defines
the keywords used in the image label area of the Clementine NIR mosaic.
PDS_VERSION_ID = PDS3
This dataset
conforms to version 3 of the PDS standards.
RECORD_TYPE = FIXED_LENGTH
This keyword defines
the record structure of the file as fixed-length
record files.
RECORD_BYTES = xxxx
Record length in
bytes for fixed-length records (number of samples *2).
FILE_RECORDS = xxxx
Total number of
fixed-length records contained in the file.
LABEL_RECORDS = x
Number of
fixed-length label records in the file.
INTERCHANGE_FORMAT = BINARY
Data are organized
as BINARY values.
^IMAGE = x
Pointer to the first
record that contains image data. (The first
record in the file
is designated as record 1.).
DATA_SET_ID
= "CLEM1-L-N-5-DIM-NIR-V1.0"
The PDS defined
dataset identifier for the Clementine NIR mosaic.
PRODUCT_ID = "NI03N003"
Unique product
identifier for this image file. This value is the same as
the file name.
(Format described in the "FILES, DIRECTORIES, AND DISK
CONTENTS"
section above.)
PRODUCER_INSTITUTION_NAME =
"UNITED STATES GEOLOGICAL SURVEY"
Identifies the
producer organization of this data product.
PRODUCT_TYPE = MDIM
This keyword
identifies the image product as a Mosaicked Digital Image
Model (MDIM).
MISSION_NAME = "DEEP SPACE PROGRAM
SCIENCE
EXPERIMENT"
The keyword
identifies the product name of the mission. (This is the
official name of the
Clementine Mission.)
SPACECRAFT_NAME = "CLEMENTINE 1"
Name of the
spacecraft that acquired the data.
INSTRUMENT_NAME = "NEAR INFRARED
CAMERA"
Name of the
instrument that acquired the image data.
INSTRUMENT_ID = "NIR"
Abbreviated name of
the instrument that acquired the image data.
TARGET_NAME = "MOON"
Target of the data
product.
FILTER_NAME =
("A","B","C","D","E","F")
Images acquired from
each filter of the NIR camera were used to
complete the
Clementine NIR DIM mosaic.
CENTER_FILTER_WAVELENGTH
= (1100.000,1250.000,1500.000,
2000.000,2600.000,2780.000)
The center filter
wavelength (nanometers) of each NIR filter.
BANDWIDTH = (60.000,60.000,60.000,
60.000,60.000,120.00)
The bandwidth
(nanometers) of each NIR filter.
START_TIME = "N/A"
STOP_TIME = "N/A"
SPACECRAFT_CLOCK_START_COUNT =
"N/A"
SPACECRAFT_CLOCK_STOP_COUNT =
"N/A"
Start_Time,
Stop_Time, and clock counts are not applicable (N/A) for
this data product
but are required keywords.
PRODUCT_CREATION_TIME
= 2006-05-25T13:30:03
Time at which the
image product was produced.
NOTE = "NIR 6-BAND
MOSAIC"
Note field always
says NIR 6-BAND MOSAIC.
OBJECT = IMAGE
BANDS = 6
There are five
spectral bands in the NIR DIM mosaic.
BAND_STORAGE_TYPE
= BAND_SEQUENTIAL
Storage order is
band sequential.
BAND_NAME = "N/A"
Band name keyword is
not applicable.
LINES = xxxx
Number of lines
(rows) in image array.
LINE_SAMPLES = xxxx
Number of samples
(columns) in image array.
SAMPLE_TYPE = MSB_INTEGER
Data are stored in
"Most Significant Byte" order
first format. This
is the storage order of Sun workstations and
Macintosh computers.
Other systems, such as IBM/PC compatible computers
and DEC/VAX systems
will need to reverse the byte order of the 16-bit
pixels before the
data can be used.
SAMPLE_BITS = 16
There are 16 bits
per sample (2 bytes).
SAMPLE_BIT_MASK
= 2#1111111111111111#
This keyword
indicates all bits within a 16-bit word are used in the
expression of the
value.
OFFSET = 0.0
SCALING_FACTOR
= 1.350000E-04
The OFFSET and
SCALING_FACTOR keywords contain values used to convert
the 16-bit integer
pixel value to radiometric units.
FRACTIONAL_REFLECTANCE
= (PIXEL* SCALING_FACTOR) + OFFSET
VALID_MINIMUM = -32752
Lowest valid value
that can be stored in pixel (always -32752).
NULL = -32768
Value of empty
pixels or missing data (always -32768).
LOW_REPR_SATURATION
= -32767
Value of pixel if
processing caused a low-end value pixel to go outside
dynamic range of a
16-bit signed integer (always -32767).
LOW_INSTR_SATURATION
= -32766
Value if pixel was
low-end saturated (always -32766). For example, if
the bias of the
camera was set so that low DN values could not be
stored in the pixel.
HIGH_INSTR_SATURATION
= -32765
Value of pixel if
processing caused a high-end value pixel to go outside
dynamic range of a 16-bit
signed integer (always -32765).
HIGH_REPR_SATURATION
= -32764
Value if pixel was
high-end saturated (always -32764). For example, if
the scene was too
bright for the image to record at the pixel value
became saturated.
MINIMUM = xxxx
Minimum value in
image array.
MAXIMUM = xxxx
Maximum value in
image array.
CHECKSUM = xxxxxxxx
Sum of all bytes in
the image object. Used to validate that an image
file was properly
stored on the media.
END_OBJECT = IMAGE
OBJECT = IMAGE_MAP_PROJECTION
^DATA_SET_MAP_PROJECTION =
"DSMAP.CAT"
Name of file
containing additional information about the map projection.
DSMAP.CAT is located
in the 'catalog' directory.
COORDINATE_SYSTEM_TYPE
= "BODY-FIXED ROTATING"
COORDINATE_SYSTEM_NAME
= "PLANETOGRAPHIC"
Coordinate system
used in the map projection.
MAP_PROJECTION_TYPE
= "SINUSOIDAL"
Name of map
projection.
MAP_RESOLUTION
= xxx.xxxxx
Map resolution
(pixels per degree) at the reference point of the
projection.
MAP_SCALE = x.xxxxxx
Map scale
(kilometers per pixel) at the reference point of the
projection.
MAXIMUM_LATITUDE
= xx.xxxxxxx
Maximum latitude of
the image file
MINIMUM_LATITUDE
= xx.xxxxxxx
Minimum latitude of
the image file.
EASTERNMOST_LONGITUDE
= xxx.xxxxxxx
Easternmost
longitude of the image file.
WESTERNMOST_LONGITUDE
= xxx.xxxxxxx
Westernmost longitude
of the image file
LINE_PROJECTION_OFFSET
= xxxxx.xxxxxxx
SAMPLE_PROJECTION_OFFSET =
xxxxx.xxxxxxx
Projection offsets
are used to define the relationship between line
and sample of the
image array and the latitude and longitude coordinate
on the surface of
the planet. See 'dsmap.cat' file located in
the 'catalog'
directory for information on these keywords.
A_AXIS_RADIUS = 1737.4000000
B_AXIS_RADIUS = 1737.4000000
C_AXIS_RADIUS = 1737.4000000
Three-axis radius of
the Moon used in the derivation of the map products
that make up the NIR
6-band mosaic.
FIRST_STANDARD_PARALLEL =
"N/A"
SECOND_STANDARD_PARALLEL =
"N/A"
Standard parallels
of map, not used in this Sinusoidal Equal-Area
projection.
POSITIVE_LONGITUDE_DIRECTION = EAST
The Moon coordinate
system uses a positive longitude direction of east.
Longitude values
increase in the eastern direction.
CENTER_LATITUDE
= 0.0
Center latitude of
the map projection.
CENTER_LONGITUDE
= xxxx.xxxx
Center longitude of
the map projection.
REFERENCE_LATITUDE
= "N/A"
REFERENCE_LONGITUDE
= "N/A"
Reference latitude
and longitudes are not used in the Sinusoidal
Equal-Area
projection.
LINE_FIRST_PIXEL = 1
SAMPLE_FIRST_PIXEL
= 1
The first pixel
(upper left) in the image array is defined as line 1,
sample 1.
LINE_LAST_PIXEL
= xxxx
SAMPLE_LAST_PIXEL
= xxxx
The last pixel
(lower right) in the image arrays is defined by these
keywords.
MAP_PROJECTION_ROTATION =
0.0000000
Map projection
rotation always 0 for the Clementine NIR DIM.
VERTICAL_FRAMELET_OFFSET =
"N/A"
HORIZONTAL_FRAMELET_OFFSET =
"N/A"
These keywords are
not applicable for the Sinusoidal Equal-Area
projection.
END_OBJECT = IMAGE_MAP_PROJECTION
END
Go
to Table of Contents.
APPENDIX B - GEOMETRIC DEFINITION OF A PIXEL
The purpose here is
to describe the spatial or geometric definition of a pixel used in the
generation and utilization of the digital image products. A broad range of
factors enters into this question. For example, is a pixel to be conceived of
as a point or as an area? The point definition would be most convenient, for
instance, when dealing with coordinate grid overlays. This results in an odd
number of pixels across a map that has an even number of spatial increments.
For changing scales (for instance by even powers of 2) this definition becomes
a problem. In this case it makes more sense to treat a pixel as a finite area.
Then an even number of pixels covers an even number of spatial increments and
decreasing/increasing scales by a power of 2 becomes trivial. However, grids
now fall between pixels, at least in a mathematical sense. Their treatment in
the generation of hardcopy therefore becomes an issue.
It was decided that
the area concept of a pixel was the better choice; we would have to live with
the asymmetries introduced in things like cartographic grids. There are various
solutions: (1) use two pixels for the width of a grid line, (2) stagger grid
pixels back-and-forth across the mathematical position, (3) use a convention
whereby grid lines are systematically drawn offset from their mathematical
position.
The next issue is
the conversion between integer coordinates and real coordinates of the pixel
mesh. We adopt the convention that pixels are numbered (or named if you like)
beginning in the upper left corner with line 1, sample 1 (pixel 1,1); lines
increase downward; samples increase to the right. (Even this is not a universal standard; some
astronomical systems begin, perhaps more logically, in the lower left corner.)
There are three reasonable possibilities for aligning a real, or floating
point, coordinate system with the pixel mesh: the coordinate 1.0, 1.0 could be
the upper left, the center, or the lower right of pixel 1,1. The convention historically used for
geometric calibration files (Reseau positions) and also used in the
Multimission Image Processing Laboratory at the Jet Propulsion Laboratory, is
that the center of the pixel is defined as its location in real coordinates. In
other words, the real coordinates of the center of pixel 1,1 are 1.0, 1.0. The top left corner of the pixel is 0.5, 0.5
and the bottom right corner is 1.49999...,1.499999. The bottom and right edge of a pixel is the
mathematically open boundary. This is the standard adopted in the image
products.
Cartographic
conventions must also be defined. The map projection representation of a pixel
is mathematically open at the increasing (right and lower) boundaries, and
mathematically closed at its left and upper boundaries. An exception occurs at
the physical limits of the projection; the lower boundary of the lowest pixel
is closed to include the limit of the projection (e.g. the south pole). The figure below shows the coordinates of
Pixel 1,1.
Coordinates of Pixel
1,1
longitude 180.0
179.00001
| |
latitude |
| line
90.0 -- ----------------- -- 0.5
| |
| |
| |
| |
| +
|
| (1.0,1.0)
|
| |
| |
| |
89.00001 -- ----------------- --
1.49999
| |
| |
sample 0.5
1.49999
We must also select
a convention for drawing grid lines for various cartographic coordinates on
planetary images and maps. The convention used for image products is that a
grid line is drawn in the pixels that contain its floating point value until
the open boundary is reached and then an exception is made so the outer range
of latitude and longitude will always appear on the image. This means, in the
example above, a 10 degree grid would start on pixel 1 and be drawn on every
tenth pixel (11, 21, 31,...) until the open boundary is reached. Then the line
would be drawn on the pixel previous to the open boundary (line 180 instead of
line 181, or sample 360 instead of 361).
To summarize, the
conventions are:
1) Pixels are
treated as areas, not as points.
2) The integer
coordinates begin with 1,1 (read, "line 1, sample 1") for the
upper-left-most pixel; lines increase downward; samples increase to the right.
3) Integer and
floating point image coordinates are the same at the center of a pixel.
4) Grids will be
drawn in the pixels that contain the floating point location of the grid lines
except for open boundaries, which will be drawn to the left or above the open
boundary.
Go to Table of Contents.