Lidar sensor¶

The lidar sensor is currently implemented as an ideal sensor that projects simulated laser beams over a cylindrical or circular field of view (FOV). The sensor’s settings specify the scan pattern and rate.

Lidar detections¶

Each beam intersecting with an object’s mesh generates a lidar return with a 3D position relative to the sensor. The intensity of the return (which is affected many factors including atmospheric conditions, reflective properties of the object, and orientation of the object) is currently not simulated.

Lidar sensor settings¶

Sample config¶

{
"sensors": [
  {
    "id": "lidar1",
    "type": "lidar",
    "enabled": true,
    "parent-link": "LidarMountPoint",
    "lidar-type": "generic-cylindrical",
    "number-of-channels": 16,
    "range" : 100,
    "points-per-second": 100000,
    "report-frequency": 0,
    "horizontal-rotation-frequency":10.0,
    "horizontal-fov-start-deg": 0.0,
    "horizontal-fov-end-deg": 360.0,
    "vertical-rotation-frequency": 0.0,
    "vertical-fov-lower-deg": -45.0,
    "vertical-fov-upper-deg": -15.0,
    "radial-scaling": 1.0,
    "disable-self-hits": false,
    "draw-debug-points": false,
    "origin": {
      "xyz": "0.6 0 0",
      "rpy-deg": "0 0 0"
    }
  }]
}

Parameter	Value	Description
`id`	string	Name of lidar sensor.
`type`	`lidar`	Sensor type specifying this as a lidar sensor.
`enabled`	bool	Whether sensor is enabled.
`parent-link`	string	Name of the link that the sensor is attached to.
`lidar-type`	string	Lidar sensor type. See below for details.
`number-of-channels`	integer	Number of simultaneous scan channels.
`range`	float	Maximum sensing range (meters.)
`points-per-second`	integer	Number of points returned per second (sensor total, not per channel.)
`report-frequency`	float	How often the sensor data is returned. See below for details. Defaults to zero meaning as frequently as possible. (≥0 Hertz, values <0.5 same as 0)
`horizontal-rotation-frequency`	float	Horizontal scan rate (revolutions per second.)
`horizontal-fov-start-deg`	float	Horizontal field of view starting angle. See below for details. (0.0 to 360.0 degrees)
`horizontal-fov-end-deg`	float	Horizontal field of view ending angle. See below for details. (0.0 to 360.0 degrees)
`vertical-rotation-frequency`	float	Vertical scan rate (revolutions per second.)
`vertical-fov-start-deg`	float	Vertical field of view starting angle. See below for details. (-90.0 to +90.0 degrees)
`vertical-fov-end-deg`	float	Vertical field of view ending angle. See below for details. (-90.0 to +90.0 degrees)
`radial-scaling`	float	Scan position scaling factor in radial direction. See below for details.
`disable-self-hits`	bool	If true, lidar traces will pass through the sensor’s owner robot to prevent self hits. Defaults to false if not specified.
`draw-debug-points`	bool	If true, markers will be rendered at the beam hit points on the detected objects. This is not supported in Unreal’s Shipping configuration. Defaults to false if not specified.
`origin`: `xyz`	string of 3 floats	Position offset “X Y Z” of the sensor relative to the parent link’s origin in meters. Defaults to all zero if `origin` is not specified.
`origin`: `rpy`	string of 3 floats	Rotation offset “Roll Pitch Yaw” of the sensor relative to the parent link’s origin in radians. Defaults to all zero if `origin` is not specified.

Point rate and report frequency¶

A sensor “report” consists of a set of 3D points detected by the sensor and their corresponding segmentation IDs. The number of points in each report varies so that the average number of points reported per second matches the points-per-second setting.

With the default report-frequency setting of zero, the sensor publishes reports as frequently as possible which is usually once per simulation step. A non-zero report-frequency of 0.5 or more sets the average report publication rate with the reports varying size to maintain the specified points-per-second overall. Note that the simulation step size affects how well the sensor can meet the report-frequency setting from report to report but the average report rate will approach the setting value.

FOV settings¶

The field of view (FOV) settings define the area where data is returned.

The horizontal-fov-*-deg settings specify the start and ending horizontal angles of the sweep area where 0° is straight ahead, increasing right (clockwise from overhead) relative to the sensor.

The vertical-fov-*-deg settings specify the start and ending vertical angles of the sweep area where +90° is straight up and -90° is straight down relative to the sensor.

A particular lidar type may ignore one or both the horizontal and vertical FOV settings. See the lidar type section below for details.

Lidar types¶

The lidar-type setting specifies sensor characteristics not specified by the other settings and may set default values for those other settings. Most importantly, lidar-type specifies the laser scan pattern.

The possible lidar-type values and their descriptions are:

Value	Description
`generic_cylindrical`	The sensor scans a cylindrical volume.
`generic_rosette`	The sensor beams scan a conical volume with a hypotrochoid curve.
`livox_mid70`	The sensor simulates a Livox Mid-70 lidar sensor.
`livox_avia`	The sensor simulates a Livox Avia lidar sensor.

Generic cylindrical lidar type¶

The generic_cylindrical lidar type is similar to the Velodyne Puck lidar sensor (https://velodynelidar.com/products/puck). It has multiple laser beams (specified by number-of-channels) which sweep out shallow horizontal cones. The laser beams are equally spaced vertically to cover the vertical FOV. The beams sweep horizontally 360°, but data is returned only when the beams are within the horizontal FOV range.

The vertical-rotation-frequency and radial-scaling settings are ignored.

Generic rosette lidar type¶

The generic_rosette lidar type has multiple laser beams (specified by number-of-channels) which sweep out a conical volume in a “rosette” pattern based on a hypotrochoid roulette curve: a “rolling circle” travels on the inside of the perimeter of a larger “fixed circle” while the “tracing point” attached at a fixed radius on the rolling circle traces out the curve. For easier configuration, generic_rosette allows the angular rate of the “rolling circle” to be specified directly through vertical-rotation-frequency rather than through ratios of the “rolling” and “fixed” circles. vertical-rotation-frequency can be negative which generates a epitrochoid curve instead (where the rolling circle travels on the outside of the fixed circle.) horizontal-rotation-frequency specifies the angular rate at which the rolling circle travels around the fixed circle.

The positions in polar coordinates of the points sampled from the rosette pattern are mapped to the directions the lasers are pointed. The polar angle is used directly as the horizontal angle of the laser. Like generic_cylindrical, the beams sweep horizontally 360° but data is only returned when the beams are within the horizontal FOV range specified by the horizontal-fov-*-deg settings.

The polar radius is mapped to the vertical FOV. The radius of the tracing point is automatically set so that the polar radius ranges from 0.0 to 1.0. A polar radius of 0.0 corresponds to vertical-fov-lower-deg while a polar radius of 1.0 corresponds to vertical-fov-upper-deg.

The radial-scaling setting fine-tunes the shape of the scanning pattern curve by scaling the tracing point’s angular offset from the rolling circle center’s angular position (as seen from fixed circle’s center,) causing the tracing point to travel in an ovoidal path around the rolling circle. A value of “1.0” (the default) leaves the curve unmodified. A value greater the 1.0 “stretches” the position of the tracing point away from the center of the rolling circle along the radial path around the center of the fixed circle. A value less than 1.0 compresses the tracing point’s position towards the center of the rolling circle. A hypotrochoid curve typically has “petals” and values greater than 1.0 widens those petals while values less than 1.0 narrows them.

Livox Mid-70 lidar type¶

The livox_mid70 lidar type simulates the Livox Mid-70 lidar sensor (https://www.livoxtech.com/mid-70). It is based on the generic_rosette lidar type with appropriate default values for the Mid-70 thus none of the lidar characteristic settings such as number-of-channels or horizontal-rotation-frequency need to be specified. These settings can still be specified, for instance, to tweak the sensor to better match an actual unit or simulate a closely related but slightly different model.

A standard livox_mid70 config would be similar to this:

{
"sensors": [
  {
    "id": "lidar1",
    "type": "lidar",
    "enabled": true,
    "parent-link": "LidarMountPoint",
    "lidar-type": "livox_mid70",
    "draw-debug-points": false,
    "origin": {
      "xyz": "0.6 0 0",
      "rpy-deg": "0 0 0"
    }
  }
}