Other work using forward looking stereo cameras for
visual odometry are presented in [6]. Reported error was less
than 3% without filtering and less than 1% in combination
with other sensors (IMU).
In [7] different algorithms are evaluated for visual
odometry using a single camera pointing perpendicular to the
ground. This method assumed planar ground, which makes
this solution sensitive to changes in the height of the camera
above the ground. Reported error was 0.3% on planar ground
and up to 7.7% on uneven grass due to calibration error.
Similar work has been done in [8] where a sensor used in optical mouse is adapted for an outdoor environment on a
mobile robot. The camera and image processing is
incorporated in a chip which gives a frame rate at 6 kHz. Two
sensors are used for calculating heading and traveled
distance, but each sensor assumes planar ground. This
assumption also makes the system sensitive to tilt of the robot
where one sensor is closer and the other is further away from
the ground. Reported error after calibration on a straight
planar surface was 0.3%.