Isaacsim 4.5.0's LiDAR simulation bug related with render dt and physics dt

Omniverse Isaac Sim
1

I’m working on simulating SLAM on Isaacsim 4.5.0 with ROS2 humble.

First, I found that simulated point cloud data using “Create RTX Lidar Scan Buffer” node includes nonsense timestamps. They includes timestamp with scale from 0 to 1e19, which cannot be interpreted as nanosec too. (I solved this timestamp issues with calculating relative time per ticks using provided equations) I’m confusing about this issue, since none of users have reported this. maybe I have done something wrong.

Second one is really strange. My simulated LiDAR’s scan rate is 10Hz. It emits 512 ticks per scan with 32 channels, and accepts 2 echos (used OS1_REV6_32ch10hz512res). Number of the maximum point cloud data returns would be 512 * 32 * 2 = 32768. However when I set my render dt differently, the number of returns varies with it. I don’t get why this happens.

My physics dt is 0.005s. (200Hz)
My render dt was set from 0.1s to 0.005s.

Number of returned point cloud data in the scan buffer for each rendering frequency was as below. (Written shape data.shape. Each scans are recorded after a single simulation_context.step(render=True) iteration.)

scan 1 - 10Hz: (0,), 50Hz: (5950, 3), 100Hz: (7497, 3), 200Hz: (7532, 3), 400Hz: (7678, 3)

scan 2 - 10Hz: (7772, 3), 50Hz: (7903, 3), 100Hz: (7776, 3), 200Hz: (15483, 3), 400Hz: (15907, 3)

scan 3 - 10Hz: (7775, 3), 50Hz: (8031, 3), 100Hz: (7776, 3), 200Hz: (23196, 3), 400Hz: (22389, 3)

scan 4 - 10Hz: (7775, 3), 50Hz: (8159, 3), 100Hz: (7777, 3), 200Hz: (25565, 3), 400Hz: (26007, 3)

Why does this happens? I don’t get why the number of return should change as I set the redering frequency differently, since all of the frequency was faster than the scan rate.

Isaac Sim Version

4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
Other (please specify):

Operating System

Ubuntu 22.04
Ubuntu 20.04
Windows 11
Windows 10
Other (please specify):

GPU Information

  • Model: RTX 3080
  • Driver Version:
3

Hi @hhnoh98 could you please give it a try with Isaac Sim 5.0? The node IsaacCreateRTXLidarScanBuffer is deprecated and replaced by IsaacExtractRTXSensorPointCloud.

4

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