Technical Specs

start (Dynamics) This starts the sensor dynamics estimation components (see Services, Section 6.3.3).
disprange (Disparity Range) The disparity range gives the maximum disparity value for each image feature re-
lated to the resolution of the high-quality disparity image (640 x 480 pixels). The disparity range determines
the minimum working distance of the visual odometry. When the disparity range is narrow, only more dis-
tant features are considered in the visual-odometry estimation. When choosing a broader disparity range,
close features can also be used. Broader disparity ranges increase processing time, which can reduce the
visual odometry’s frame rate.
nkey (Number of Keyframes) More keyframes can increase the robustness and accuracy of the visual odometry,
but they also increase processing time and can decrease the visual-odometry frame rate.
ncorner (Number of Corners) This value gives the approximate number of corners that will be detected in the
left image. Larger numbers make visual odometry more robust and accurate but can lead to lower frame
rates of the visual odometry.
nfeature (Number of Features) This value is the maximum number of features that will be derived from the
corners. It is useful to detect more corners and select the best subset as features. Larger numbers make
visual odometry more robust and accurate but can lead to lower visual-odometry frame rates. Fewer features
might be computed, depending on the scene and movement. The actual number of features is reported below
the camera image on the Web GUI’s Dynamics page.
Note: Increasing the number of keyframes, corners, or features will also increase robustness but will require
more computation time and may reduce the frame rate, depending on other components active on the rc_visard.
The visual-odometry frame rate should be at least 10 Hz.
6.4.2 Services
The visual odometry component offers the following services for persisting and restoring parameter settings. The
names of the corresponding Web GUI buttons are added in brackets:
save
_
parameters (Save) With this service call, the current parameter settings of the visual odometry component
are persisted to the rc_visard. That is, these values are applied even after reboot.
This service requires no arguments.
This service returns no response.
reset
_
defaults (Reset) Restores and applies the default values for this component’s parameters (“factory re-
set”).
Warning: The user must be aware that calling this service causes irrecoverable loss of the visual
odometry component’s current parameter settings.
This service requires no arguments.
This service returns no response.
This component offers no start or stop services itself, because the dynamics component (Section 6.3) starts and
stops it.
6.5 Stereo INS
The stereo-vision-aided Inertial Navigation System (INS) component is part of the sensor dynamics component.
It combines visual-odometry measurements with inertial measurement unit (IMU) data and provides robust, low
latency, real-time state estimates at a high rate. The IMU consists of three accelerometers and three gyroscopes,
6.5. Stereo INS 47