Adds body tracking option to ViewerCfg

[KyleM73]

Description

Resolves Issue #1534 by adding non-root body tracking as an option in the ViewerCfg. See the issue for justification/discussion. API as follows:

• Adds origin_type "asset_body"
• Adds field "body_name"

When origin_type = "asset_body" and "body_name" matches a body in the asset specified in "asset_name", the viewport is configured to track the link frame of the body in world coordinates. By using the existing eye and lookat fields in ViewerCfg the additional features are enabled:

• Tracking the end effector of an arm during manipulation (see below)
• Tracking a fixed offset from the end effector of an arm (e.g. mimicking the view of a wrist-mounted camera)
• Tracking a mobile base using the currently-supported workaround for lack of wheel physics by defining a virtual arm to mimic the motion of the robot

Type of change

• New feature (non-breaking change which adds functionality)

Training Video from "Isaac-Lift-Cube-Franka-v0" after 1000 iterations.

Viewer defined as follows:

viewer = ViewerCfg(eye=(0.5, 0.5, 0.0), origin_type="asset_body", env_index=0, asset_name="robot", body_name="panda_hand")

No other changes were made from the default environment definition.

Video_1024_franka_asset_body_test.mp4

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[kellyguo11]

Thanks for adding support for this!