Non-static transform from base_link to camera

[MikeWrockAIS]

I noticed that even though you can set the frame in which to publish the ZED's odometry information, the current TF is not used. For example: if the camera is on a moving arm, when the arm moves the camera will publish odometry as if base_link moved, ignoring the current base_link to camera transform. Is there any way to tell the zed-wrapper the camera moves relative to base link during operation?

[Myzhar]

Hi @MikeWrockAIS the default URDF is designed for robots with the camera statically linked to base_link, but you can change it according to your configuration.

In your case you can simply change the type of joint between zed_camera_center and base_link from fixed to floating https://github.com/stereolabs/zed-ros-wrapper/blob/master/zed_wrapper/urdf/zed.urdf#L25

In this way the robot_state_publisher will not publish the relative TF, but you should do it in one of your nodes, otherwise the TF of the ZED will result as broken.

[MikeWrockAIS]

Does it have to be the zed_camera_center to base_link joint that is floating or can it be one joint along the TF tree such as: base_link -> rotating_arm (floating) rotating_arm -> zed_camera_center (fixed)

[Myzhar]

It depends on your configuration. You should modify the ZED URDF according to how the camera is linked on the robot. The important thing is that the chain zed_camera_center -> .... -> base_link is not broken and the ROS TF can always calculate the zed_camera_center -> base_link transform

[MikeWrockAIS]

It seems like once a valid transform from camera to base link is acquired mCamera2BaseTransfValid is set to true. Since the transform is only updated if mCamera2BaseTransfValid is false, I don't see how providing an up to date TF tree helps. Perhaps I should set mCamera2BaseTransfValid to false or simply remove the if statement and call getCamera2BaseTransform() every time?

[Myzhar]

Yes, in your case you must update it at every cycle so you must remove the check. We will add a parameter to discriminate between static and not static transform.

[MikeWrockAIS]

awesome, thanks a lot

[Myzhar]

I keep the issue open as reminder for the feature to be added

[tugbakara]

I have a smilar issue, tomorrow I will open a new issue and add the details.