Marker Set

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What is a Marker Set?

Most of the RoCKIn benchmarks require to track robot pose. To do this, RoCKIn uses a motion capture ("mocap") system. What the mocap system actually tracks is a RoCKIn-designed Marker Set (see picture on the right) comprising 5 IR-reflective spherical markers.

One of the Marker Sets used for the 2015 RoCKIn Competition. The base of the Marker Set fits within a 170 mm diameter circle.

For this reason, each robot partecipating to the Competitions must be fitted with a Marker Set. Marker Sets will be sent to the teams in advance.

Mounting the Marker Set on your robot

The base of the Marker Set is a 4 mm thick laser-cut plywood element. You should mount the Marker Set so that:

  • its base is horizontal (parallel to the floor);
  • its pose wrt the odometry reference system of your robot is mechanically fixed;
  • the X axis on the Marker Set points in the "forward" direction of your robot (the Marker Set is arrow-shaped as a reminder);
  • it's located high on your robot (possibly on top).

The last requirement is important, as it ensures that the Marker Set is always visible from the mocap cameras; these are mounted all around the testbed, 4 m (for RoCKIn@Home) or 3 m (for RoCKIn@Work) from the ground.

To affix the marker to your robot's frame you can use the holes on its base. Hole diameter is 4 mm, and holes are spaced 20 mm from each other. Just make sure that the marker cannot move at all; moreover, make there should be no screws or other fixing elements rising more than 1 cm above the Marker Set base, otherwise they will mask the visibility of the reflective spheres.

The robot must avoid collisions between the Marker Set and other objects (when assessing collisions for scoring, the Marker Set is considered as a part of the robot).

Capturing the rototranslation between odometry system and Marker Set system

The mocap system captures the pose of the Marker Set, while the benchmarks require the pose of the robot. In order to obtain the second from the first, during the set up days RoCKIn personnel will capture the rototranslation between the "odometry" reference system of each robot and the reference system of the Marker Set.

Therefore, during the setup days (November 19 and 20, 2015) each team will have to subject its robot to the capture process. This process takes a few minutes, and requires:

  • to place the robot (fitted with the marker set) in a predefined spot;
  • to align the X and Y axes of the "odometry" reference system of the robot with those marked on the ground.

The captured rototranslation will be later communicated to the teams. This will allow them to check it, and (after the Competition) to extract robot-centered pose data from the (marker-centered) Ground Truth data published by RoCKIn.