Technical Specs

Description of run-time parameters
Run-time parameters influence the number of features used to compute visual odometry. More features increase
the visual odometry’s robustness at the expense of more run time, which can reduce the frame rate. Although the
resulting state estimate will always have a high frequency due to fusion with IMU measurements, high visual-
odometry frame rates are nevertheless desirable, since these measurements are much more accurate than IMU
measurements alone. A visual-odometry rate of at least 10 Hz should thus be aimed for. The visual-odometry
frame rate is provided as a status parameter and is shown below the camera image on the Web GUI’s Dynamics
page.
Fig. 6.4.1: The Web GUI’s Dynamics tab
The camera image shown on this page depicts image features as small green dots. The bold green dots are the
features in the current image for which correspondences could be found in a previous keyframe. Green lines
depict the motion of these features relative to the previous keyframe. This visualization should help to find a good
set of parameters for visual odometry. The number of correspondences is reported as a status parameter and is
shown below the camera image on the Web GUI’s Dynamics page. For robust visual-odometry measurements, the
parameters should be adjusted so that the resulting number of correspondences in the target environment is around
at least 50 when the sensor is moving. The correspondence count will be larger when the rc_visard is static, and
the number will change when the rc_visard moves through the environment. Short failures of the visual odometry
are tolerated due to the fusion with IMU measurements. Longer failures should be avoided because they lead to
large pose uncertainties and can lead to errors in the state estimation.
Each run-time parameter is represented by a row on the Web GUI’s Dynamics tab. The name of the row is given
in brackets behind the parameter name, and the parameters are listed in the order they appear in the Web GUI:
6.4. Visual odometry 46