Workspace alignment

RCARS by default creates its own gravity aligned workspace frame. As long as no Precalibrated Workspace is used, this frame is not positioned at a specific location. However, sometimes it is important to know where the estimate of RCARS lies with respect to a given frame. To obtain such information, we provide functionality for static or dynamic alignment.

TF alignment

To achieve alignment, we use ROS' TF package. This allows for visualization in Rviz but also provides functionality to directly obtain any given transformation in the tree of transformations. Our alignment procedure allows to align with an given, external frame published by some other node or with a new frame statically published. One use case is to align the rcars frame to an already published robot frame or to a ground truth pose from a motion capture system.

Alignment can be specified as ROS parameters for the rcars_visualization/tf_publisher node. This node takes the following parameters

• Enable/disable workspace alignment

#!bash

    /rcars/tf_publihser/align_workspace

• Define RCARS frame to align. This can be any frame including tag frames, IMU frame, camera frame etc.

#!bash

    /rcars/tf_publihser/frame_rcars

• Define alignment frame. This should be an already published frame. To use this, you have to specify external alignment (see below). Otherwise this value is ignored.

#!bash

    /rcars/tf_publisher/frame_align

• Use external alignment frame. If true, this assumes the frame to align to is already published by some other node (see frame_align above). If set to false, a new frame to align to is published.

#!bash

    /rcars/tf_publisher/useExternalCalibration

• Pose of alignment tag. If no external frame to align to is specified, a new frame can be published automatically. These variables specify the location and orientation of the frame. The position is expressed in the world frame and the orientation is specified as the rotation from tag to world expressed in Euler Angles.

#!bash

    /rcars/tf_publisher/WrWTX /WrWTY /WrWTZ
    /rcars/tf_publisher/qWTX /qWTY /qWTZ

For more information or for an example check rcars_visualization/launch/visualization.launch.