Errors that cause official examples CRASH

[Walkism]

Describe the bug
Official example crashes after error AttributeError: 'NoneType' object has no attribute 'GetCamera' and RuntimeError: "/World/viewer_camera" is not a valid Usd.Prim or UsdGeom.Camera.

To Reproduce
I followed installation guidance strictly. In local installation as well as the official container, simply run an example such as
python -m omnigibson.examples.scenes.scene_selector
(choose scene model [1] and then [2] for Full Load)
or
python -m omnigibson.examples.environments.behavior_env_demo
(choose [2] for Full Load)
After running the command, needless to do anything, the program crashes with the following errors (in random time, usually after several seconds):

Traceback (most recent call last):
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.widget.viewport/omni/kit/widget/viewport/impl/texture.py", line 355, in on_drawable_changed
self.__drawable_changed_fn(texture['rp_resource'], event.payload.get('presentation_key', 0))
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.widget.viewport/omni/kit/widget/viewport/widget.py", line 465, in __set_image_data
vp_api._sync_viewport_api(camera, canvas_size, vp_api.time, view, projection, force_update=True)
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.widget.viewport/omni/kit/widget/viewport/api.py", line 544, in _sync_viewport_api
self.__projection = self._conform_projection(policy, camera, image_aspect, canvas_aspect, projection)
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.widget.viewport/omni/kit/widget/viewport/api.py", line 473, in _conform_projection
gf_camera = camera.GetCamera(self.__time)
AttributeError: 'NoneType' object has no attribute 'GetCamera'
Traceback (most recent call last):
File "/home/asus/isaacsim-4.1.0/extsPhysics/omni.physx.ui/omni/physxui/scripts/extension.py", line 82, in on_stage_update
cam_pos = camera.position_world
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.viewport.utility/omni/kit/viewport/utility/camera_state.py", line 100, in position_world
return self.usd_camera.ComputeLocalToWorldTransform(self.__time).Transform(Gf.Vec3d(0, 0, 0))
File "/home/asus/isaacsim-4.1.0/kit/exts/omni.kit.viewport.utility/omni/kit/viewport/utility/camera_state.py", line 87, in usd_camera
raise RuntimeError(f'"{self.__camera_path}" is not a valid Usd.Prim or UsdGeom.Camera')
RuntimeError: "/World/viewer_camera" is not a valid Usd.Prim or UsdGeom.Camera

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 20.04
• Isaac Sim Version: 4.1.0
• OmniGibson Version: 1.1.1
• Hardware: i7-13700 (32GB RAM), RTX A4500 (20GB VRAM)

Additional context
I saw a similiar issue which is replied to safely "ignore" the error. However I find it hard to ignore these errors with naive annotation. Could anyone kindly help with these errors? Thanks so much in advance!

[RongkunYang]

I meet the same problem too, looking forward for the solving method.

[hang-yin]

Hi @Walkism , thanks for reporting this! Just to clarify, this happens randomly when you run any example scripts?

[Walkism]

Hi, thanks for your attention! (Sorry for the late reply, I missed the notification in github.)
The error happens randomly in every scene provided in omnigibson.examples.scenes.scene_selector plus omnigibson.examples.environments.behavior_env_demo and omnigibson.examples.environments.navigation_env_demo, and the error reports in terminal log are practivally the same, containing two python error traceback, as shown in the initial bug report.
I have studied the problem a bit. I find that the direct cause of the crash seems to be the failure of getting the viewer_camera prim, in form:
stage.GetPrimAtPath("/World/viewer_camera") -> invalid null prim
which applies to both of the python error traceback. Specificly, they are:
prim = self.__ensure_usd_stage().GetPrimAtPath(vp_api.camera_path) in method ViewportWidget.__set_image_data in file exts/omni.kit.widget.viewport/omni/kit/widget/viewport/widget.py
and
camera_prim = self.__viewport_api.stage.GetPrimAtPath(self.__camera_path) in method ViewportCameraState.usd_camera in file exts/omni.kit.viewport.utility/omni/kit/viewport/utility/camera_state.py
Both call would return invalid null prim at random time simultaneously (as shown in the terminal log), resulting in subsequent crash.

However,

the very first example in omnigibson documentation omnigibson.examples.robots.robot_control_example run perfectly without crash. I also noticed the difference between them: regarding setting viewer_camera,
examples.robots.robot_control_example uses og.sim.viewer_camera.set_position_orientation(...)
while
examples.scenes.scene_selector and other examples with error uses og.sim.enable_viewer_camera_teleoperation(),
which further enables keyboard teleoperation of the camera.

The following images shows the location of the two culprits. Hope this would give a better view of the problem.

Looking forward to the problem being solved. I'm glad to provide more information or try more scenario if needed!

[Walkism]

Wow sorry, I think I might have found what actually happened😂. These "crash" behaviors are the result of the simulation ending naturally. The sim loop is too short (max_iterations=10), which makes the simulation end feel a bit abrupt. Together with the Python error stack, the fearsome "segmentation fault", and a flood of warnings from Isaac Sim, it all makes the natural termination look like a "crash".
After increasing the number of simulation cycles sufficiently, everything looks fine now.
(Now I understand why it is replied to "safely ignore" the error in this similiar issure. )
Perhaps it's also the case for @RongkunYang ? Hope this explains the problem for anyone facing the same trouble.