Noise not being applied to the Points publisher of GpuLidar sensor

[oceanusxiv]

On a high level this can be replicated by running the SubT virtual course. The command used is:

ign launch -v 4 tunnel_circuit_practice.ign robotName1:=X1 robotConfig1:=X1_SENSOR_CONFIG_3

X1_SENSOR_CONFIG_3 is supposed to contain a 3D Lidar, and the output looks like

There's clearly no noise even though the stddev defined in the sdf specifies 0.01 noise. This does not occur for the 2D Lidars which output a LaserScan message instead. GpuLidar internally publishes both LaserScan and PointCloud messages, via the GpuLidarSensor::Update method which calls this->PublishLidarScan(_now); from the Lidar base class.

The issue here is that the noise is only applied to the range data in the Lidar base class, in https://github.com/ignitionrobotics/ign-sensors/blob/8ee625a405264ca697fbefc0e8a9b1ae6d1b53dd/src/Lidar.cc#L229 which is called here https://github.com/ignitionrobotics/ign-sensors/blob/8ee625a405264ca697fbefc0e8a9b1ae6d1b53dd/src/GpuLidarSensor.cc#L233 That interior call doesn't update the laser buffer itself, merely taking a copy here https://github.com/ignitionrobotics/ign-sensors/blob/8ee625a405264ca697fbefc0e8a9b1ae6d1b53dd/src/Lidar.cc#L234 so the actual laser buffer remains unchanged. As a result the outer GpuLidarSensor::Update only has access to the original clean lidar ranges, hence why it publishes point clouds with no noise.

The solution here is probably to separate out an ApplyNoise function in Lidar that will properly alter the this->laserBuffer and call it before both this->PublishLidarScan(_now); and this->dataPtr->FillPointCloudMsg(); so it can be accessed by both classes.

[ahcorde]

Hello

I tested de GPU lidar with the example world in ign-gazebo, the noise it's being added to the rays. See the following gif:

The values which contain the maximum range value are not adding the noise. But in your image I think all of them are colliding with something.

[iche033]

I think the the visualization in ign-gazebo shows lidar scan data which has noise correctly applied but the issue is that the point cloud data that are published over the ~/<topic_name>/points topic doesn't have any noise applied.

[ahcorde]

The plugin uses a subscriber to get the data: https://github.com/ignitionrobotics/ign-gazebo/blob/ign-gazebo4/src/gui/plugins/visualize_lidar/VisualizeLidar.cc#L381

[acschang]

Resolved in #86