Improve custom cameras support in MujocoVisualizer and MujocoVideoRecorder

[diegoferigo]

• The MujocoVisualizer can now be opened with a configuration¹ that initializes the camera towards a specific target. Then, the user is free to roam around interactively.
• Users can now create more generic custom cameras from an extended set of parameters².
• The jaxsim.mujoco.RodModelToMjcf.convert function now accepts also MujocoCamera objects of a sequence of such objects, removing the need to serialize them to dictionary. However, for the most generic camera support, the method still accepts a plain dictionary or list of dictionaries.
• The default track camera of the MujocoVideoRecorder is now more explicit as it is defined as default argument.

I found interesting the approach used to specify the initial viewpoint of the interactive viewer. It seemed to me much easier to setup than the parameters necessary to create a custom camera. We might think to understand what is the mapping logic between them, and provide a new MujocoCamera.build_from_target_view helper.

I eventually found the time to also implement this approach. Now having the recorder taking exactly the same image that is shown by default in the interactive viewer should be straightforward. Furthermore, we can now use the interactive viewer to find the desired view, and then use the resulting parameters in the recorder.

with viz.open(azimut=-180, distance=5, elevation=-30) as viewer:

    with viewer.lock():
        ...

    viz.sync(viewer=viewer)

    while viewer.is_running():
        time.sleep(0.500)

mjcf_string, assets = jaxsim.mujoco.RodModelToMjcf().convert(
    rod_model=model.built_from,
    heightmap=True,
    heightmap_samples_xy=(51, 51),
    cameras=jaxsim.mujoco.loaders.MujocoCamera.build(
        name="recorder_cam", mode="fixed", fovy="60", pos="0 0 10.0", quat="1 0 0 0"
    ),
)

[...]

recorder.record_frame(camera_name="recorder_cam")

mjcf_string, assets = jaxsim.mujoco.RodModelToMjcf().convert(
    rod_model=model.built_from,
    heightmap=True,
    heightmap_samples_xy=(51, 51),
    cameras=jaxsim.mujoco.loaders.MujocoCamera.build_from_target_view(
        camera_name="recorder_cam",
        lookat=jnp.zeros(3),
        distance=5,
        azimut=-180,
        elevation=-30,
        degrees=True,
    )
)

[...]

recorder.record_frame(camera_name="recorder_cam")

---

📚 Documentation preview 📚: https://jaxsim--206.org.readthedocs.build//206/

Footnotes

1. https://mujoco.readthedocs.io/en/stable/XMLreference.html#visual-global ↩

2. https://mujoco.readthedocs.io/en/stable/XMLreference.html#body-camera ↩

[flferretti]

Thanks! I left some comments

[diegoferigo]

I spotted a bug in the computation of camera parameters from the desired view. Solved in https://github.com/ami-iit/jaxsim/compare/f0e6f0c1b075e664cfcbc1236729ba6035594d09..b25c33837794a796eda85e1121f6327b379e47c8.

[flferretti]

Why is this necessary?

[diegoferigo]

This was just a maintenance dependecy bump. Since readthedocs built successfully, I thought why not updating to the latest python version. Did you have any reason to stay one version behind?

[flferretti]

It's okay to update the default Python version used in the build environment, I was just wondering if it was a constraint for scipy

[diegoferigo]

Nope no reason. I was just passing through the yaml file and I saw this pinning that could have been updated.