International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
Figure 5. Stereomapping with MER MI images in SOCET
SET based on relative orientation without a priori informa-
tion. Left, anaglyph from two overlapping MI frames
obtained by MER-B (Opportunity) rover in Meridiani
Planum. Region shown is ~3 cm high. Spherules (informally
known as "blueberries") are hematite-rich concretions a few
mm in diameter. A third MI frame (not shown) provided
stereo coverage overlapping this pair to the right. Upper
right: Orthomosaic with contours of "clevation" (in camera-
aligned local coordinate system, hence essentially range)
derived from the two overlapping stereopairs. CI 250 um
with 1000 um index contours; range precision is 30 um.
Lower right: perspective view from top, no exaggeration.
constraint is quite weak. As a preliminary approach to our
analysis, we demonstrated that a relative orientation of a MI
stereopair can be performed in SOCET SET without a priori
orientation information (except that the two camera stations
were at the best-focus distance from the target, with roughly
similar pointing) or constraints. Figure 5 illustrates a
microscopic DEM obtained in this way. In order to merge MI
images with Pancam color data, however, it is necessary to
model the constrained motions of multiple cameras in a
consistent coordinate system.
4.3 Methodology
We are mecting the requirement to merge MI and Pancam
images by implementing a very general processing software
design that includes models of all the MER cameras (except
the Hazcams, which could easily be added), their constrained
motions, and a large number of related coordinate frames
needed to describe these motions. Processing is generally
divided into "2D" steps performed in ISIS and "3D" steps
done in SOCET SET, as described in Section 3, and in detail
resembles the approach developed for the Pancam-like
Imager for Mars Pathfinder (Gaddis et al., 1999; Kirk et al.,
1999). This includes the implementation of a series of
projections relevant to lander/rover data as opposed to
global cartography, such as panoramic, planimetric, and
oblique orthographic. Bundle-adjustment software must be
implemented in ISIS because the SOCET SET adjustment
module cannot incorporate the needed constraints. Finally,
the SOCET SET stereomatching software is not designed to
handle images at multiple azimuths and high elevations
relative to the coordinate grid. ISIS must therefore be used
to supply SOCET SET with the orientation of each stereopair
in a "local" coordinate frame with its Z axis roughly parallel
to the camera boresights. DEMs and orthoimages can be
produced in this system and transformed back to a "global"
coordinate frame in the process of exporting them back to
ISIS for further processing.
The Mars Pathfinder mission had only one camera system on
a fixed lander, and hence had one "local" coordinate frame
i Sy = aan P EZ : eX
Figure 6. Left: Controlled mosaic (~1500 pixels wide) of
two MER-A MI frames showing 4.5-cm area of rock
"Mazatzal" partly cleared of dust by brushing with Rock
Abrasion Tool. Center: Quasi-natural color Pancam image
of same area, resolution ~0.5 mm/pixel. Right: MI and
Pancam images merged show correlation of color, texture.
(fixed in the camera head) and one key "global" frame (fixed
in the lander and oriented to the vertical and north),
Processing software for Pathfinder (including bundle
adjustment) was therefore implemented by hard-coding the
single type of local-global transformation. For MER, this
software had to be generalized to handle coordinates local to
several cameras, intermediate coordinates used to model the
motion of the Pancam mast and instrument arm, and "global"
coordinate frames both moving with the rover and fixed at
the initial landing point or subsequent sites of exploration.
Fortunately, a powerful mechanism for computing the trans-
formations between the many coordinate frames has been
provided by the NASA Navigation Ancillary Information
Facility (NAIF; http://pds-naif.jpl.nasa.gov). NAIF supplies
Frames Kernels (or F-Kernels) that define the relations
between all coordinate frames used by MER (and other
missions) in terms of C-Kernels and SP-Kernels that contain
the rotations and translations, respectively, between frames.
The C- and SP-Kernels can be time-dependent and are
continuously updated as the mission proceeds. Routines in
the NAIF software library can then be used to obtain the
transformation linking any frame to any other at any time.
By using the NAIF kernels and library routines, we are able
to compute the a priori orientation of any MER camera in
any frame of interest, which allows us to transfer images into
SOCET SET, perform unconstrained bundle adjustments
there, make DEMs and orthomosaics, and transform these
back into ISIS. This capability suffices to make MI products
and merge them with Pancam data (Figure 6). We are
currently working to extend the NAIF software to compute
the partial derivatives of the frame transformations, and to
implement a bundle-adjustment program based on the
modified frames software. This adjustment program will
permit us to make controlled panoramic and planimetric
mosaics of Pancam and Navcam images, and to reconstruct
the paths of the rovers by linking images obtained from
successive stops (cf. Li et al., 2004; Xu, 2004).
ACKNOWLEDGEMENTS
We thank the many individuals at the USGS, Flagstaff who contributed
to the work reported: I. Anderson, B. Archinal, J. Barrett, K. Becker,
D. Cook, G. Cushing, E. Eliason, L. Gaddis, D. Galuszka, T. Hare, E.
Howington-Kraus, C. Isbell, J. Johnson, B. Redding, M. Rosiek, L.
Soderblom, R. Sucharski, T. Sucharski, T. Titus, and J. Torson. The
work was supported by the following NASA programs: Mars Data
Analysis, Mars Express Mission, and Mars Exploration Rovers
Mission.
REFERENCES
Albertz, J., et al., 1992. The camera experiments HRSC and
WAOSS on the Mars 94 mission. Int. Arch. Photogramm
Remote Sens., 29(B1), pp. 130-137.
Archinal, B.A., et al., 2004. Preparing for THEMIS controlled
global Mars mosaics. Lunar Planet. Scil, XXXV, Abstract #
1903, Lunar and Planetary Institute, Houston (CD-ROM).
Bell, J.F., III, et al, 2003. Mars Exploration Rover Athena
Panoramic Camera (Pancam) investigation. J. Geophys. Res.
108(E12), 8063, doi: 10.1029/2003JE002070.
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