Lidar points are not accurate towards scene representation.

[sriceumich]

We are evaluating this as an alternative to our lidar simulator and seem to be having a few issues with the points generated. The lidar points are not accurately representing the scene and have a curve to them, points closer to the lidar have more of a curve. The noise doesn't seem to be representative of a lidar in the scene causing detection to seem inaccurate. Noise adjustment does not seem to compensate for this issue. I tried the various lidar that were represented and all seemed to exhibit this issue.

Curved floor with wide noise paths.

Extra thick points which should be a wall.

[RyodoTanaka]

@sriceumich
Thank you for your issue.
This problem looks comes from depth buffer, I think.
For the implementation, we use depth buffer image as raw data, and transform that image into distance value.

@Autumn60
If you have any opinion (mainly depth-buffer transform part), I am glad to hear that.

[Autumn60]

@sriceumich
Could you tell me which script file (RaycastLiDARSensor.cs or DepthBufferLiDARSensor.cs) you are using for LiDAR simulation?

[sriceumich]

@Autumn60 I am using the DepthBufferLiDARSensor currently for this and the 32 beam configuration. The RaycastLiDARSensor is presenting it's own set of challenges. We noticed some additional issues in the sensor this past week as we prepared for a paper. As we started moving the ego, the sensor started exhibiting some broken details the further away the beams are. We attempted to use the points for our methods, but with the noise we were unable to produce good results from them.

[Autumn60]

@sriceumich

As you say, DepthBufferLiDAR has poor accuracy at long distances.
This is because the DepthBuffer values provided by Unity are not linear with respect to the actual distance.

Also, the lower the resolution of the RenderTexture used, the less accurate the point cloud.
It may be difficult to provide enough pixels for a high quality LiDAR such as the VLS-128.

[Autumn60]

It is possible that the part that calculates the corresponding pixel index from the laser direction is wrong, but I don't know the exact cause yet now.
(Perhaps the calculation of the camera distortion matrix...? 🤔 )

[Autumn60]

Based on some experiments, I am convinced that the calculation to find the texture pixels from the laser direction is wrong.

https://github.com/Field-Robotics-Japan/UnitySensors/blob/master/Assets/UnitySensors/Runtime/Scripts/Sensors/LiDAR/DepthBufferLiDAR/DepthBufferLiDARSensor.cs#L93-L118