How to Use GPU Lidar in AirSim

AirSim supports a GPU accelerated Lidar for multirotors and cars. It uses a depth camera that rotates around to simulate a Lidar while exploiting the GPU to do most of the work. Should allow for a large increase in amount of points that can be simulated.

The enablement of a GPU lidar and the other lidar settings can be configured via AirSimSettings json. Please see general sensors for information on configuration of general/shared sensor settings.

Note that this sensor type is currently not supported for Multirotor mode. It only works for Car and Computervision.

Enabling GPU lidar on a vehicle

  • By default, GPU lidars are not enabled. To enable the sensor, set the SensorType and Enabled attributes in settings json.
        "GPULidar1": { 
             "SensorType": 8,
             "Enabled" : true,
  • Multiple GPU lidars can be enabled on a vehicle. But one has to turn off DrawDebugPoints!

Ignoring glass and other material types

One can set an object that should be invisible to LIDAR sensors (such as glass) by giving them an Unreal Tag called LidarIgnore.

GPU Lidar configuration

The following parameters can be configured right now via settings json. For some more information check the publication on this topic here.

Parameter Description
NumberOfChannels Number of channels/lasers of the lidar. When set to 1 it will act as a 2D horizontal LiDAR and will use the VerticalFOVUpper value as the vertical angle to scan.
Range Range, in meters
MeasurementsPerCycle amount of measurements in one full cycle (horizontal resolution)
RotationsPerSecond Rotations per second
Resolution Defines the resolution of the depth camera image that generates the Lidar point cloud
HorizontalFOVStart Horizontal FOV start for the lidar, in degrees
HorizontalFOVEnd Horizontal FOV end for the lidar, in degrees
VerticalFOVUpper Vertical FOV upper limit for the lidar, in degrees
VerticalFOVLower Vertical FOV lower limit for the lidar, in degrees
X Y Z Position of the lidar relative to the vehicle (in NED, in meters)
Roll Pitch Yaw Orientation of the lidar relative to the vehicle (in degrees, yaw-pitch-roll order to front vector +X)
IgnoreMarked Remove objects with the Unreal Tag MarkedIgnore from the sensor data
GroundTruth Generate ground truth segmentation color values
DrawSensor Draw the physical sensor in the world on the vehicle with a 3D axes shown where the sensor is
External Uncouple the sensor from the vehicle. If enabled, the position and orientation will be relative to Unreal world coordinates in NED format from the settings file.
ExternalLocal When in external mode, if this is enabled the retrieved pose of the sensor will be in Local NED coordinates(from starting position from vehicle) and not converted Unreal NED coordinates which is default
GenerateIntensity Toggle intensity calculation on or off. This requires a surface material map to be available. See below for more information.
rangeMaxLambertianPercentage Lambertian reflectivity percentage to max out on. Will act linear to 0% for below.
rainMaxIntensity Rain intensity maximum to scale from in mm/hour.
rainConstantA Constant one to to calculate the extinction coefficient in rain
rainConstantB Constant one to to calculate the extinction coefficient in rain 
{
    "SeeDocsAt": "https://github.com/Cosys-Lab/Cosys-AirSim/tree/main/docs/settings.md",
    "SettingsVersion": 1.2,

    "SimMode": "SkidVehicle",

     "Vehicles": {
        "airsimvehicle": {
            "VehicleType": "CPHusky",
            "AutoCreate": true,
            "Sensors": {
                "gpulidar1": {
                    "SensorType": 8,
                    "Enabled" : true,
                    "External": false,
                    "NumberOfChannels": 128,
                    "Range": 50,
                    "Resolution": 512,
                    "RotationsPerSecond": 10,
                    "MeasurementsPerCycle": 1024,
                    "X": 0, "Y": 0, "Z": -0.3,
                    "Roll": 0, "Pitch": 0, "Yaw" : 0,
                    "VerticalFOVUpper": 45,
                    "VerticalFOVLower": -45,
                    "HorizontalFOVStart": 0,
                    "HorizontalFOVEnd": 360,
                    "DrawDebugPoints": true,
                    "DrawMode": 4,
                    "Resolution": 1024,
                    "IgnoreMarked": true,
                    "GroundTruth": false
                    "GenerateIntensity": true,
                    "rangeMaxLambertianPercentage": 80,
                    "rainMaxIntensity": 70,
                    "rainConstantA": 0.01,
                    "rainConstantB": 0.6,
                }
            }
        }
    }
}

Intensity Surface Material map

If 'GenerateIntensity' is enabled in the settings json, a surface material map is required. This map is used to calculate the intensity of the lidar points. e.g.:

wood,0.9
alluminium,0.5
concrete,0.3
asphalt,0.1

This needs to be saved as 'materials.csv' in your documents folder where also your settings json file resides.

Server side visualization for debugging

By default, the lidar points are not drawn on the viewport. To enable the drawing of hit laser points on the viewport, please enable setting 'DrawDebugPoints' via settings json. This is only for testing purposes and will affect the data slightly. It also needs to be disabled when using multiple Lidar sensors to avoid artifacts!!

e.g.:

        "Lidar1": { 
             ...
             "DrawDebugPoints": true
        },

You can also tweak the variation of debugging with the 'DrawMode' parameter: - 0 = no coloring - 1 = instance segmentation - 2 = material - 3 = impact angle - 4 = intensity

e.g.:

        "Lidar1": { 
             ...
             "DrawDebugPoints": true,
             "DrawMode": 4 
        },

Client API

Use getGPULidarData(sensor name, vehicle name) API to retrieve the GPU Lidar data. The API returns a Point-Cloud as a flat array of floats along with the timestamp of the capture and lidar pose.

  • Point-Cloud: The floats represent [x,y,z, rgb, intensity] coordinate for each point hit within the range in the last scan.
  • Lidar Pose: Default: sensor pose in the vehicle frame / External: If set to External(see table) the coordinates will be in either Unreal NED when ExternalLocal is false or Local NED (from starting position from vehicle) when ExternalLocal is true.

Rgb represents a float32 representation of the RGB8 value that is linked to the instance segmentation system. See the Image API documentation and the instance segmentation documentation. The float32 comes from binary concatenation of the RGB8 values :rgb = value_segmentation.R << 16 | value_segmentation.G << 8 | value_segmentation.B\ It can be retrieved from the API and converted back to RGB8 with for example the following Python code:

lidar_data = client.getGPULidarData('lidar', 'vehicle')
points = np.array(lidar_data.point_cloud, dtype=np.dtype('f4'))
points = np.reshape(points, (int(points.shape[0] / 5), 5))
rgb_values = points[:, 3].astype(np.uint32)
rgb = np.zeros((np.shape(points)[0], 3))
xyz = points[:, 0:3]
for index, rgb_value in enumerate(rgb_values):
  rgb[index, 0] = (rgb_value >> 16) & 0xFF
  rgb[index, 1] = (rgb_value >> 8) & 0xFF
  rgb[index, 2] = rgb_value & 0xFF