QUESTION:
Does the Sojourner use a digital terrain model (DTM) to help it navigate? Is
a DTM constructed from the cameras on the lander? If so, is this done in the
lander or computed back on Earth and then uploaded to the lander? What is
the focal length of the cameras on the lander and over what range can
mapping be accurately acheived?

ANSWER from David Mittman on July 18, 1997:
The rover itself does not have a DTM on-board. It is commanded in either
absolute moves (e.g, go forward three wheel spins) or in an xy coordinate
system defined around the lander (e.g., go to waypoint at x=3.2m, y=6.4m).
There is a digital terrain map constructed within the Rover Control
Workstation. It is derived from stereo imagery and is used to help the Rover
Driver assess the trafficability of the terrain surrounding the rover. The
DTM allows the Rover Driver to "fly" over the area surrounding the Rover and
get an improved view of the rockiness, slope, etc. Neither the lander nor
the rover makes native use of a DTM. Each eye of the IMP has a field of view
of 14.4 degrees, and provides effective stereo coverage for Rover use out to
about 10 meters.