TF2 Question about frame conversion

Question

I modeled the following robot with an urdf file. Thanks to a robot state publisher, i have access to the static tfs between camera_link and base_link.

I'm using orb_slam3 library as SLAM algorithm. This algorithm gives me a tf between the camera_link and to camera_link at time 0 (i call it "cam0"). My question is the following : How to convert this tf to a tf between base_link and map ?

I tried lookup for the tf between camera_link and base_link, and then do :

tf_map_base_link = tf_base_link_camera_link * tf_cam0_camera_link

But when I set "tf_cam0_camera_link" to the identity tf, compute "tf_map_base_link" and publish it as a tf between map and base_link, I visualize the following on rviz :

As you can see, camera_link and map frames are now superimposed. I don't understand why.

Here is my tf tree :

Can you help me ? Cheers

Answer 1

I proceeded by tinkering to obtain a correct transformation. There's probably a better option, but here's what i did :

 tf2::Transform tf_final;    //tf base_link --> map
 tf_final = (tf_camera_base_link.inverse() * tf_camera_cam0 * tf_camera_base_link).inverse();

 tf2::Vector3 vec = tf_final.getOrigin();
 tf_final.setOrigin(-vec);

 tf2::Quaternion q_final = tf_final.getRotation();
 tf2::Quaternion q_inverted(-q_final.x(), -q_final.y(), -q_final.z(), -q_final.w());
 tf_final.setRotation(q_inverted);

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