Technical Specs

which measure accelerations and turn rates in all three dimensions. By fusing IMU and visual-odometry measure-
ments, the state estimate has the same frequency as the IMU (200 Hz) and is very robust even under challenging
lighting conditions and for fast motions.
Note: To achieve high-quality pose estimates, it must be ensured that sufficient texture is visible during runtime
of the stereo INS component. In case no texture is visible for a longer period of time, the stereo INS component
will stop instead of providing highly erroneous data.
6.5.1 Self-Calibration
During startup of the stereo INS component, it will self-calibrate the IMU using the visual-odometry measure-
ments. For the self-calibration to succeed, it is required that
• the rc_visard is not moving and
• sufficient texture is visible
during startup of the stereo INS component. Failure to meet these requirements will most likely result in a constant
drift of the pose estimates.
6.5.2 Parameters
The stereo INS component’s node name is rc
_
stereo
_
ins.
This component has no run-time parameters.
This component reports the following status values.
Table 6.5.1: The rc
_
stereo
_
ins component’s status values
Name Description
freq Frequency of the stereo INS process in Hertz. This value is shown as Update Rate in the Web GUI
Overview tab in the Dynamics area
state String representing the internal state
6.6 Camera calibration
To use the stereo camera as measuring instrument, camera parameters such as focal length, lens distortion, and the
relationship of the cameras to each other must be exactly known. The parameters are determined by calibration
and used for image rectification (see Planar rectification, Section 6.1.2), which is the basis for all other image
processing modules. The rc_visard is calibrated at production time. Nevertheless, checking calibration and re-
calibration might be necessary if the rc_visard was exposed to strong mechanical impact. The camera calibration
component is responsible for checking calibration and recalibrating.
6.6.1 Self-calibration
The camera calibration component automatically runs in self-calibration mode at a low frequency in the back-
ground. In this mode, the rc_visard observes the alignment of image rows of both rectified images. A mechanical
impact, such as one caused by dropping the rc_visard, might result in a misalignment. If a significant mis-
alignment is detected, then it is automatically corrected. After each reboot and after each correction, the current
self-calibration offset is reported in the camera component’s log file (see Downloading log files, Section 9.7) as:
“rc_stereocalib: Current self-calibration offset is 0.00, update counter is 0”
The update counter is incremented after each automatic correction. It is reset to 0 after manual recalibration of the
rc_visard.
6.6. Camera calibration 48