Pelvis Marker Transformation

Transformation from the OptiTrack pelvis marker to an upper-body reference thread.

Define the static tf to know where the "reference screw" is on the robot:

rosrun tf2_ros static_transform_publisher 0.13121 0.0175 0.34875 0 0 0 torso_link reference_screw

If you use the optitrack board (https://git.ias.informatik.tu-darmstadt.de/talos/TU_Darmstadt/STL_Files/-/blob/main/Kangaroo/HipMarker/KangarooMarker.stl?ref_type=heads) with 3 markers, following transform can be used from the reference_screw to the single marker

rosrun tf2_ros static_transform_publisher 0.018341 0.018591 -0.023462 0 0 0 reference_screw reference_marker

After that, add a optitrack rigid body for the 3 markers and move the center of it on that exact reference_marker (+ manually align the rotations between optitrack and tf). Then, you can publish a tf that links both trees (optitrack and robot) such that reference_marker and the optitrack marker equal.

About torso_link->reference_screw transform

The shown transformation defines the spatial relationship between the OptiTrack rigid body frame pelvis_2_link and a mechanical reference thread located in the upper body of the Kangaroo robot.

This transformation can be used as an initial starting transformation to integrate the Kangaroo robot into the OptiTrack coordinate system. It serves as a reasonable initial guess for subsequent refinement or calibration steps (e.g. hand–eye calibration or optimization-based alignment).