URDF Import creates duplicate “ghost” static colliders due to detached colliders Scope.
Detailed Description
I am encountering an issue with the URDF Importer where it generates a duplicate set of colliders: one that correctly moves with the robot, and another “ghost” collider that remains static at the spawn point.
When importing a URDF, the importer creates a colliders prim of type Scope for organization. However, this Scope does not seem to inherit the transform updates of the parent link properly.
Using the Physics Debugger, I observed that there are two colliders for a single link:
Of course, this static ghost collider also has collision properties.
This is just one example URDF, but I have confirmed that the same issue occurs with other URDF as well.
Is there a configuration to prevent this duplication or force the colliders Scope to behave as a proper child of the link?
Steps to Reproduce
Import a robot URDF (using urdf_importer extension)
Additional Information
What I’ve Tried
I have observed this issue in version 5.0.0 as well, so it seems to be a regression introduced in version 5.0.0 or later. In version 4.5.0, the import process worked correctly without generating these detached ghost colliders.
Is this behavior tied to a particular URDF, or do you see it with several different robots? It does not reproduce here when importing exts/isaacsim.asset.importer.urdf/data/urdf/robots/ur10/urdf/ur10.urdf.
If possible, please share:
A minimal URDF that still shows the duplicate “ghost” colliders
A short screen recording of the issue, including the exact URDF importer options and any steps you take after import (e.g., enabling the Physics Debugger, moving the robot, etc.)
I have observed the same issue with other URDF files as well. First, I would like to share an example using the robot arm I shared previously. This is the Unitree D1 robot arm (I have included a download link for the URDF file.). (I apologize that the mouse cursor is not visible in the videos due to a graphics glitch.)
Video 1: The following video shows my URDF import steps and the selected options. You can see that “ghost colliders” appear the moment the model is imported. Also, when I manually move the individual colliders after importing, you can observe that these ghost colliders are attached to the specific colliders located within the colliders Scope.
Video 2: In this video, I visualized the colliders for each link using the Physics Debugger. (I understand that this allows me to view colliders that would normally require disabling the instanceable property on the collisions to be seen). I then moved the joints using the Physics Inspector. As you can see, while the standard colliders attached to each link move along with the links, the “ghost colliders” remain static and do not move.
Additional Note:
I am visualizing the colliders with the setting set to “All”.
I suspect the root cause lies in how the colliders scope is handled in versions 5.0.0 and 5.1.0 compared to 4.5.0.
In Isaac Sim 4.5.0, the colliders scope (or the referenced meshes) did not hold active collider properties. However, in 5.0.0 and 5.1.0, the prims inside the colliders scope seem to have active collider properties directly assigned to them. This structural change appears to be creating the static ghost collisions that were not present in previous versions.
I would like to know if there is a way to disable these unintended collisions, or if this issue is specific to my environment/setup.
I was able to reproduce the issues, but may not have time to look into it right now. So it would be very helpful if you could also try this on Isaac Sim 6.0.0?
