Ray Caster isn't working for my Robot

[ValdezNewton]

Hi everyone! I'm quite new to NVIDIA Isaac Lab. I've converted my robot from URDF to USD and I'm able to move all joints of the robot successfully. However, the Ray Caster doesn't seem to work on my robot. To debugg the issue, I tried using the raycaster_sensor.py script from https://isaac-sim.github.io/IsaacLab/main/source/overview/core-concepts/sensors/ray_caster.html on my lunar environment. The ray caster sensors work successfully as shown in Image 1. However, when I try to use ray caster on my robot, the red points (representing either point cloud or LiDAR rays) aren't appearing as they do on the anymal robot, as shown in Image 2.

When I ran my code that uses Ray Caster for my robot, I received errors as shown below:

  File "/home/isaac-a6000/nvidia-isaac-sim/IsaacLab/source/isaaclab/isaaclab/sensors/ray_caster/ray_caster.py", line 329, in _debug_vis_callback
    self.ray_visualizer.visualize(viz_points)
  File "/home/isaac-a6000/nvidia-isaac-sim/IsaacLab/source/isaaclab/isaaclab/markers/visualization_markers.py", line 334, in visualize
    raise ValueError("Number of markers cannot be zero! Hint: The function was called with no inputs?")
ValueError: Number of markers cannot be zero! Hint: The function was called with no inputs?
Traceback (most recent call last):
  File "/home/isaac-a6000/nvidia-isaac-sim/IsaacLab/source/isaaclab/isaaclab/sensors/sensor_base.py", line 159, in <lambda>
    lambda event, obj=weakref.proxy(self): obj._debug_vis_callback(event)
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

My initial thought was because I didn't create a dedicated location for the Ray Caster. Therefore, I created a lidar_link cylinder shape and use a Fixed Joint to attach it to my chassis, and place the ray caster on that cylinder, but it failed, and prompted the same errors as shown above.

The part of the code that I've written that uses Ray Caster is shown below. I've uploaded my Python scripts for full details on my code:

# 360-Degree LiDAR for Obstacle Avoidance
LUNARBOT_LIDAR_CFG = RayCasterCfg(
    prim_path="{ENV_REGEX_NS}/Robot", 
    offset=RayCasterCfg.OffsetCfg(pos=(0.0, 0.5, 0.35)), 
    ray_alignment="yaw", 
    pattern_cfg=patterns.LidarPatternCfg(
        channels=1, 
        vertical_fov_range=(0.0, 0.0),
        horizontal_fov_range=(-180.0, 180.0), 
        horizontal_res=5.0, 
    ),
    max_distance=15.0, 
    debug_vis=True, # Will now generate exactly 72 markers per robot!
    mesh_prim_paths=["/World/Terrain"], 
)

Information on the environment:
The environment consists of multiple lunar rocks and four walls that borders the vicinity of the ground plane. The lunar rocks and the four walls are merged together as a single mesh. The merged mesh contains Collision API but no rigid body property. The lunar rocks have a height higher than 5 meters.

Information on my robot (LunarBot):
My LunarBot was converted from URDF to USD. All joints are working, and I can move it just like a regular robot. It can also collide with the lunar rocks in the environment. However, I'm unable to use Ray Caster on it.

Image 1:

Image 2:

Image 3:

lunarbot_cfg.py
lunarbot_raycaster.py

Can someone kindly help me in this matter? I hope to learn more from everyone!