| DATA_SET_DESCRIPTION |
Data Set Overview
=================
Mars Pathfinder bounced down and rolled to a stop on the surface
of Mars on July 4, 1997. After a slight delay in deployment due
to airbags draped over one of the lander's petals, the Rover
rolled down onto the surface of Mars at 5:37am, July 6, 1997
(UTC).
627 images were collected by the three cameras mounted on the
Microrover Flight Experiment (also known as the Mars Pathfinder
Rover or Sojourner). The rover had two monochromatic cameras
mounted in front which provided stereo viewing, and a separate
'color' camera mounted in the rear. The rear camera obtained
color pictures through the use of red, green, and blue pixels
arranged in a 'field-staggered 3G' mosaic filter pattern on the
CCD.
The Rover Camera MIDR data set is composed of four different
kinds of products: uncorrected black and white mosaics,
uncorrected color mosaics, CAHV-corrected color mosaics, and
stereo anaglyphs. The 'uncorrected' mosaics have had some
limited radiometric corrections applied to them but no geometric
corrections. The CAHV-corrected mosaics have had both
corrections applied.
Parameters
==========
The Rover Camera MIDRs are images; the main parameter is light,
measured in units of data numbers or DNs. Each CCD pixel
(picture element) is represented by a byte value ranging from 0
(dark) to 255 (saturated). The wavelength sensitivity of the
front (black and white) cameras was 830 to 890 nm; the aft
(color) camera sensitivity was 500 to 900 nm. Since the MIDRs
combine multiple EDRs acquired at varying light levels and
exposure durations, the MIDR pixels can have light levels greater
than 255. (See the more detailed explanation in the 'Processing'
section below.)
Processing
==========
The input products used to generate the Rover Camera Mosaicked
Image Data Records (MIDRs) were the Rover Camera Experiment Data
Records (EDRs), (data set id MPFR-M-RVRCAM-2-EDR-V1.0), also
archived on this CD. The identity of individual EDRs used as
input to a specific MIDR can be determined using the
COMMAND_SEQUENCE_NUMBER item in the PDS label of each MIDR.
The Rover Camera MIDRs consist of the reconstruction of multiple
subframes acquired at approximately the same time, from the same
physical location. In other words, there was no movement of the
rover between subframes; there were radiometric but no spatial
changes from one subframe to another. The purpose of subframing
was to optimize the exposure times in different portions of a
reconstructed image, while utilizing the full dynamic range of
the CCD. For example, the top half of a Rover image may have
received significantly more light than the shadowed lower half,
and would therefore benefit from a shorter exposure time.
The lowest level MIDR products are the black and white
uncorrected mosaics. These products were created using the VICAR
(Video Image Communication and Retrieval) program MPFRVRMOS.
MPFRVRMOS mosaicked multiple rover subframes from one image. It
applied rudimentary dark current and exposure corrections to the
mosaic. It did this first by subtracting a dark level from the
DN values of all component frames. (This value is indicated by
the DARK_LEVEL_CORRECTION keyword in the labels.) It then
synthetically generated an 'output' exposure duration equal to
the longest exposure duration of any input subframe. It
equalized the exposures of the various subframes by multiplying
the DN values in each input frame by the ratio of the
synthetically generated exposure duration over the input exposure
duration. The entire DN range of every input frame was retained
by converting the byte data to half word data at this stage.
Finally, the program applied a dark current correction to the
mosaic. This could be done in one of two ways indicated by the
DARK_CURRENT_CORRECTION_TYPE keyword in the PDS labels. The
valid types of correction were PRIME and BOTH; PRIME applied only
a vertical correction on the front camera images, or only a
horizontal correction on the rear camera images. BOTH meant that
both a vertical and a horizontal correction were applied.
The products generated by this process were the '.HAF' images in
the RVR_MIDR/RVR_MOS/ directory. These images were then
converted back to byte data using the VICAR program CFORM. This
resulted in the '.IMG' images in the same directory.
The next level of MIDR products are the color uncorrected
mosaics, produced from EDRs acquired by the rear rover camera.
These products were essentially created through the same process
as the black and white mosaics, except that after the mosaic had
been radiometrically corrected, it was run through the program
MPFRVRCLR, which generated three separate color bands from the
single input band. (In one case only, for image
RVR_MIDR_CLR-1253414310-S076054-REAR-B, the image was split into
three separate bands before being radiometrically corrected.) As
described elsewhere (see RCRRINST.CAT on this CD), the rear
camera CCD contained pixels sensitive to different wavelengths of
light, enabling it to obtain a 'color' picture with a single
exposure. This single band was split up by using a color map,
and applying bilinear spatial interpolation to fill in the
'missing' pixels.
This step of the process also resulted in both half word and byte
data files, stored in the directory RVR_MIDR/RVR_CLR/ on the CD.
(Technically, since the CFORM program only worked on
single-banded files, the images were split into three separate
red, green, and blue files using COPY, converted to byte using
CFORM, and recombined into a single file using MPFCOMBO.)
The next step of process involved the application of a geometric
correction to the mosaics using the CAHV camera model. This step
was applied to both the black and white and the color mosaics.
The half word data files were used as input. This step was
accomplished using the VICAR program MPFCAHV. This program
converted the images from distorted (CAHVOR) to linear (CAHV)
coordinates. The coordinates of each pixel in the output image
were transferred from CAHV to CAHVOR space. If the pixel fell
within the input image, its DN value was bilinearly interpolated
and placed within the output image. A full output image was
created even if the input image was only a subframe. The output
image was converted to byte data by the MPFCAHV program. These
images are stored in the RVR_MIDR/RVR_CAHV/ directory on the CD.
All of the above products were generated at the Multimission
Imaging Processing Laboratory, at the Jet Propulsion Laboratory.
The highest level of MIDR products, the stereo anaglyphs, were
generated by the Microrover Flight Experiment Team, also at JPL.
The Sojourner Rover anaglyphs were created using the left and
right images captured by the rover on Mars. The following text,
provided by Tam Nguyen of the MFEX Team, describes the conversion
process which involved two platforms: a Sun Sparc20 and a Mac
PowerPC.
A. The Sun Sparc20 process:
1. The input left and right images had been previously camera
corrected by MIPL, applying the CAHV camera model.
2. These CAHV image files were then converted to PIC format using
the 'cahv2pic' command (developed by Todd Litwin for the Mars
Pathfinder Project). The 'fisheye' warping effect caused by
the rover cameras' wide angle lenses was corrected using the
'dowarp' command (also developed by Todd Litwin).
3. The unwarped images were then converted to GIF format using the
'pic2gif' command (again developed by Todd Litwin) for
compatibility with Adobe PhotoShop format constraints.
B. The Mac PowerPC process:
The creation of the rover anaglyph was performed using the Adobe
PhotoShop Version 3.0 program on a Mac PowerPC, employing the
following steps:
1. A pair of left and right rover images in GIF format were
opened. The right image was converted to RGB format by
selecting 'Mode: RGB image'.
2. The 'FrameImage' (a dashed box) in the top left corner Tool
palmlet was selected, then used to frame the left image by
holding down the left mouse button and dragging the mouse to
identify the selected area of the image.
3. The 'Edit: Copy' menu item was selected to copy the selected
image to a buffer.
4. The right image was selected by clicking on it.
5. The Layers/Channels/Paths palmlet was opened by selecting
'Windows: Show Channels'.
6. The 'Channels' option in the Layers/Channels/Paths palmlet was
selected, then the 'Red' channel only was selected (identified
by an eye in the left hand side box). The 'Edit: Paste'
command was used to paste the left image (in the buffer) into
the 'Red' channel of the right image.
7. The 'Green' and 'Blue' channels of the Layers/Channels/Paths
palmlet, identified by the eyes in the left hand side boxes,
were selected to bring the green and blue colors of the right
image back.
8. Wearing red and blue stereo viewing goggles, the 'Move' icon
(a hand in the top left corner of the Tool palmlet) was
selected. The arrow cursor then became a hand cursor. The
cursor was moved into the selected red image area, then the
left mouse button was held down. The red image was dragged
until the anaglyph showed the desired results, then the left
mouse button was released.
9. The 'FrameImage' feature was used to eliminate the unwanted
area of the anaglyph, and then the image was saved.
The anaglyph PDS labels were created using the PDS information
from the CAHV files. The 'cahvlbl' command (developed by Todd
Litwin) extracted the PDS information from the the CAHV files,
which was then converted into the correct PDS format using the
'greppds' command (developed in the Tcl language by Tam Nguyen
for the Mars Pathfinder Project).
Since the process of creating an anaglyph required the left and
right images, the PDS label of an anaglyph could contain the
information from either the left or the right image, but not
both. The unwarping and anaglyph creation processes resulted in
anaglyphs with image sizes smaller than their original images.
The rover camera models of all of the pds labels were the same.
The anaglyph creation technique described above was developed by
Tim Parker for the Mars Pathfinder Project.
Data
====
The Rover images on this CD are uncompressed, 8- and 16-bit
files, labeled in conformance with PDS standards. Both black
and white and color images are present in the data set. The
color images are stored as three separate bands in a single file.
The Rover Camera MIDRs are contained in the RVR_MIDR/ directory
on the CD. The uncorrected black and white mosaics are stored in
the RVR_MIDR/RVR_MOS/ subdirectory, the uncorrected color mosaics
are stored in the RVR_MIDR/RVR_CLR/ subdirectory, the
CAHV-corrected mosaics are stored in the RVR_MIDR/RVR_CAHV/
subdirectory, and the stereo anaglyphs are stored in the
RVR_MIDR/RVR_GLYF/ subdirectory.
Individual filenames consist of the instrument identifier 'R',
followed by a five digit command sequence number, followed by a
single letter, used as a counter. The command sequence number
used in each mosaic filename is the lowest of the command
sequence numbers from the input EDRs which make up that mosaic.
(For the stereo anaglyphs, this is the lowest of the EDRs in the
RIGHT frame.) The counter is used to distinguish between multiple
mosaics which have identical command sequence numbers. (The only
time this occurs is for command sequence '0', used when the
rover acquired images autonomously while in an emergency mode,
and for command sequence numbers in the 55xx range, which were
erroneously repeated.)
For all but the anaglyph images, the filename then contains one
of 'L', 'C', or 'R', indicating a LEFT, RIGHT, or COLOR image.
(The anaglyphs, obviously, are combinations of both LEFT and
RIGHT images.)
Finally, this is followed by one of the two file extensions,
'.IMG' or '.HAF'. The '.IMG' extension is used for byte (8-bit)
data, and the '.HAF' extension is used for half-word (16-bit)
data.
Note that the Rover Team delivered the stereo anaglyphs with
different filenames that what have been used on the CD. The
files were renamed partly to comply with PDS file naming
guidelines, and partly to provide correspondence between these
images and the other MIDRs on the CD. A mapping between the old
and new names is provided here for reference:
005101-BOTH.{jpg,pds} --> R05101A.{JPG,IMG}
05524A-BOTH.{jpg,pds} --> R05524A.{JPG,IMG}
05524B-BOTH.{jpg,pds} --> R05524B.{JPG,IMG}
14099-BOTH.{jpg,pds} --> R14094A.{JPG,IMG}
15130-BOTH.{jpg,pds} --> R15130A.{JPG,IMG}
24057-BOTH.{jpg,pds} --> R24057A.{JPG,IMG}
27093-BOTH.{jpg,pds} --> R27093A.{JPG,IMG}
32092-BOTH.{jpg,pds} --> R32092A.{JPG,IMG}
37082-BOTH.{jpg,pds} --> R37082A.{JPG,IMG}
(The JPEG versions of the above files have been placed in the
BROWSE directory of the CD.)
The filenames can be used to correlate the different kinds of
MIDRs. In other words, files in different directories of the CD
which have identical filenames, are related. For example:
RVR_MOS/R24057AR.HAF - half-word version of uncorrected black
and white mosaic of EDRs in the command
sequence number range of 24057 - 24060
RVR_MOS/R24057AR.IMG - byte version of the same mosaic
RVR_CAHV/R24057AR.IMG - CAHV-corrected version of the same
mosaic
RVR_GLYF/R24057A.IMG - stereo anaglyph version of the same
mosaic; note that this RIGHT frame
mosaic is combined with the LEFT frame
mosaic of EDRs in the range of
24053 - 24056
(Note that there is NO correspondence between R00000AL.IMG and
R00000AR.IMG.) For all of the MIDRs, the command sequence numbers
of the input EDRs are included in the PDS label. These values
can be used to backtrack to the raw products which make up a
mosaic.
For all MIDRs, the SPACECRAFT_CLOCK_STOP_COUNT shown in the label
is the SPACECRAFT_CLOCK_START_COUNT from the latest input EDR
used in the mosaic.
Note that the EXPOSURE_DURATION used in the MIDR labels has a
different meaning than that used in the EDR labels; it is a
synthetically generated value as described above in the
'Processing' section.
Some of the keyword values shown in the labels of the anaglyph
images are the values for the right frame of the mosaic; the
values for the left frame are not included. (However, the
COMMAND_SEQUENCE_NUMBER can be used to determine all the input
EDRs, and therefore the missing values.)
The best way to identify rover images that can be used as stereo
pairs is to find left and right images that have the same values
for the ROVER_HEADING and ROVER_POSITION. The 'Flight Rover
Image Status Report', put together by the Rover Team, may also be
of assistance. This report is contained in the
DOCUMENT/ROVERDOC/DOWNLINK/TABLIMAG.HTM file on this CD.
All image files are stored with a fixed length record format.
There is an attached PDS label at the beginning of each image
file that describes the content and format of the image. If the
PDS label size is not an exact multiple of the file record
length, padding is added after the end of the PDS label. Thus,
the image object always starts on a record boundary.
PDS labels are object-oriented. The object to which the label
refers (e.g., IMAGE, TABLE, etc.) is denoted by a statement of
the form:
^object = location
in which the carat character ('^', also called a pointer in this
context) indicates that the object starts at the given location.
For an object in the same file as the label (as is the case for
the Rover MIDRs), the location is an integer representing the
starting record number of the object (the first record in the
file is record 1). For example:
^IMAGE = 22
indicates that the IMAGE object begins at record 22 of the file.
A complete description of the PDS file format is available from
the Planetary Data System. (Complete contact information for the
PDS is available in the AAREADME file in the root directory of
this CD.)
Coordinate Systems and Image Geometry
=====================================
The Rover heading and position are measured in the Martian Local
Level coordinate frame. The heading is measured clockwise from
north in units of BAMs (Binary Angle Measurements), where 2**16
BAMs equals one revolution. The position is provided as x and y
offsets in meters north and east, respectively, of the Lander.
The Martian Local Level Coordinate Frame is a right handed,
orthogonal, frame whose origin is co-incident with the origin of
the Lander Coordinate Frame. The XM axis points north, the YM
axis points east, and the ZM axis points down. This system is
defined relative to the Mars areocentric coordinate system.
For more information on Mars Pathfinder coordinate systems, see
the [MELLSTROM&LAU1996], [WELLMAN1996B], and [VAUGHAN1995]
references.
Software
========
The Rover MIDR images can be displayed on UNIX, Macintosh, and PC
platforms using the PDS developed program, NASAView. This
software is freely available from the PDS Central Node and may be
obtained from their web site at http://pds.jpl.nasa.gov/. For
more information or help in obtaining the software, contact the
PDS operator at the following address:
Address: Planetary Data System, PDS Operator
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
Phone: (818) 354-4321
Email: pds_operator@jpl.nasa.gov
WWW URL: http://pds.jpl.nasa.gov/
The real time processing of the VICAR-formatted Rover data was
done using the VICAR suite of image processing programs. The
latest version of the VICAR program XVD may also be used for
displaying PDS formatted images. For information on obtaining
VICAR, please contact:
Address: Danika Jensen
M/S 168-414
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
Phone: (818) 354-6269
Email: Danika.Jensen@jpl.nasa.gov
WWW URL: http://www-mipl.jpl.nasa.gov/vicar.html
Media / Format
==============
The Rover Camera MIDR data are stored on compact disc-read only
memory (CD-ROM) media. The CD is formatted according to ISO-9660
and PDS standards. The data files do not include extended
attribute records (XARs), and are therefore not readable on some
older VMS operating systems.
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