Technical Specs
6.3 Sensor dynamics
The dynamics component provides estimates of the sensor state. These include pose, linear velocity, linear ac-
celeration, and rotational rates. The component handles starting and stopping, and streaming of the estimates for
individual subcomponents:
• Visual odometry (rc
_
stereovisodo) estimates the camera’s motion from the motion of characteristic im-
age points in the left camera images (Section 6.4).
• Stereo INS (rc
_
stereo
_
ins) combines visual odometry measurements with readings from an inertial
measurement unit (IMU) to provide accurate, high-frequency state estimates in real time (Section 6.5).
• SLAM (rc
_
slam) performs simultaneous localization and mapping (SLAM) for correcting accumulated
poses (Section 7.1).
Note: Using Stereo matching in parallel to the dynamics component may lead to decreased localization accu-
racy. See Visual odometry for how to avoid this.
6.3.1 Coordinate frames for state estimation
The world coordinate frame for state estimation is defined as follows: The coordinate frame’s z-axis points upward
and is aligned with the gravity vector. The x-axis is orthogonal to the z-axis and points in the rc_visard’s viewing
direction at the time when the pose estimation starts. The world frame’s origin is located at the origin of the
rc_visard’s IMU coordinate frame at the instant when state estimation is switched on.
If pose estimation is switched on when the rc_visard’s viewing direction parallels the gravity vector (with a
tolerance range of 10 degrees), then the world coordinate frame’s y-axis is aligned either with the IMU’s positive
or negative x-axis. In this orientation, the initial alignment of the world coordinate frame is no longer continuous.
Thus, special care has to be taken when pose estimation has to be started at such an orientation.
x
IMU
y
IMU
z
IMU
z
Cam
x
Cam
y
Cam
x
IMU
y
IMU
z
IMU
z
Cam
x
Cam
y
Cam
Pose at t=0
Current pose
z
W
x
W
y
W
Fig. 6.3.1: Coordinate frames for state estimation. The IMU coordinate frame is inside the rc_visard’s housing.
The camera coordinate frame (Section 3.7) is in the focal point of the left camera.
The transformation between the IMU coordinate frame and the camera/sensor frame is also estimated and provided
in the real-time dynamics stream over the rc_dynamics interface (see Interfaces, Section 8).
6.3. Sensor dynamics 40