Tinker-Twins/AprilTag

Coordinate System

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yyashpatel commented

Hello,

I had a few questions about the representations -

  1. the pose matrix from the result variable (https://github.com/Tinker-Twins/AprilTag/blob/main/scripts/apriltag.py#L665) - it represents the pose of the april Tag with respect to the camera ?

  2. And if I inverse the pose matrix it will give the pose of the camera with respect to the april Tag ?

  3. how is the april Tag coordinate frame (xyz direction) represented and is it at the center of the tag ?

Thanks

Tinker-Twins commented

Following are the answers to your questions:

  1. The pose result will return a 4x4 homogeneous transformation matrix of the AprilTag marker w.r.t. camera, for all detected markers in camera's FOV.
    Homogeneous Transform
  2. Inverse transformation of homogeneous transformation matrix returned by the pose result will in fact describe the relative pose of camera w.r.t. AprilTag marker.
  3. The frame for AprilTag marker(s) is assigned at the center of each marker x-axis (red color) pointing towards right, y-axis (green color) pointing forward and z-axis (blue color) pointing upward (out of the plane).
    Axis Convention

Hope this helps, all the best!