Laser Scanner Sensors

Generic laser range sensors

This is a generic sensor class used to emulate laser range scanners, including a variety of SICK and Hokuyo sensors.

This sensor works by generating a series of rays in predefined directions, and then computing whether any active object is found within a certain distance from the origin of the sensor.

The resolution and detection range can be completely configured using the MORSE Builder API. This will generate a flat mesh with a semi-circular shape, where its vertices represent the directions in which the rays of the sensor are cast. It is also possible to create a sensor with multiple scan layers, such as the SICK LD-MRS. This is configured using the parameters specified below.

Note

Objects in the scene with the No collision setting in their Game properties will not be detected by this sensor

SICK LMS500	SICK LD-MRS
Hokuyo

LaserScanner with remission values

Remission “is the reflection or scattering of light by a material.” (http://en.wikipedia.org/wiki/Remission_%28spectroscopy%29)

The level “rssi” adds a list of remission values to the LaserScanner. If a ray during the scan hits an object the rssi-value is the specular intenisty of the object’s material; If it does not hit an object with a material the remission value is set to 0.

The intensity of the material can be changed in Blender (Property -> Material -> Specular -> Intensity). The important options are highlighted in the first image.

Specular intensity of a material in Blender

Example of the LaserScanner with remission values

In the second image the sensor is illustrated. Above every box the material properties and a corresponding excerpt from the socket stream is displayed.

Note

The remission values are not comparable to any physical remission value and are not calculated. They are just based on a property of a visual effect.

Configuration of the scanning parameters

The number and direction of the rays emitted by the sensor is determined by the vertices of a semi-circle mesh parented to the sensor. The sensor will cast rays from the center of the sensor in the direction of each of the vertices in the semi-circle.

Three preconfigured scanners are available: a SICK LMS500 laser scanner, a Hokuyo and a SICK LD-MRS. The example below shows how to add them in a simulation:

from morse.builder import *

# Append a sick laser
sick = Sick() # range: 30m, field: 180deg, 180 sample points

hokuyo = Hokuyo() # range: 30m, field: 270deg, 1080 sample points

sick_ld_mrs = SickLDMRS() # range: 30m, field 100deg, 4 layers, 400 points per layer

All these default parameters can be changed i(cf Configuration parameters below). An example of how to change the arc object using the Builder API is show below:

from morse.builder import *

# Append a sick laser
sick = Sick()
sick.properties(resolution = 5)
sick.properties(scan_window = 90)
sick.properties(laser_range = 5.0)

Note

In some special cases (like multi-robot setups), you may need to additionally call sick.create_sick_arc() after setting your scanner properties.

The ray will be created from (-window/2) to (+window/2). So the range_list will contain the range clockwise.

Another example for the SICK LD-MRS:

from morse.builder import *

sick = SickLDMRS()
sick.properties(Visible_arc = True)
sick.properties(resolution = 1.0)
sick.properties(scan_window = 100)
sick.properties(laser_range = 50.0)
sick.properties(layers = 4)
sick.properties(layer_separation = 0.8)
sick.properties(layer_offset = 0.25)

As with any other component, it is possible to adjust the refresh frequency of the sensor, after it has been defined in the builder script. For example, to set the frequency to 1 Hz:

sick.frequency(1.0)

Configuration parameters for Laser Scanner Sensors

You can set these properties in your scripts with <component>.properties(<property1>=..., <property2>=...).

• laser_range (float, default: 30.0)

  The distance in meters from the center of the sensor to which it is capable of detecting other objects.

• resolution (float, default: 1.0)

  The angle between each laser in the sensor. Expressed in degrees in decimal format. (i. e.), half a degree is expressed as 0.5. Used when creating the arc object.

• scan_window (float, default: 180.0)

  The full angle covered by the sensor. Expressed in degrees in decimal format. Used when creating the arc object.

• Visible_arc (boolean, default: False)

  if the laser arc should be displayed during the simulation

• layers (integer, default: 1)

  Number of scanning planes used by the sensor.

• layer_separation (float, default: 0.8)

  The angular distance between the planes, in degrees.

• layer_offset (float, default: 0.125)

  The horizontal distance between the scan points in consecutive scanning layers. Must be given in degrees.

Available functional levels

Functional levels are predefined abstraction or realism levels for the sensor.

• raw (default level) raw laserscanner: Laserscan with point_list and range_list

  At this level, the sensor exports these datafields at each simulation step:

  • point_list (list, initial value: []): Array that stores the positions of the points found by the laser. The points are given with respect to the location of the sensor, and stored as lists of three elements. The number of points depends on the geometry of the arc parented to the sensor (see below). The point (0, 0, 0) means that this ray has not it anything in its range
  • range_list (list, initial value: []): Array that stores the distance to the first obstacle detected by each ray. The order indexing of this array is the same as for point_list, so that the element in the same index of both lists will correspond to the measures for the same ray. If the ray does not hit anything in its range it returns laser_range

  Interface support:

  • ros as sensor_msgs/LaserScan (morse.middleware.ros.laserscanner.LaserScanPublisher) or as sensor_msgs/PointCloud2 (morse.middleware.ros.laserscanner.PointCloud2Publisher)
  • socket as straight JSON serialization (morse.middleware.socket_datastream.SocketPublisher)
  • yarp as YarpLaserScannerPublisher (morse.middleware.yarp.laserscanner.YarpLaserScannerPublisher)
  • moos as LIDARNotifier (morse.middleware.moos.sick.LIDARNotifier)

• rssi laserscanner with rssi: Laserscan with point_list, range_list and remission_list

  At this level, the sensor exports these datafields at each simulation step:

  • point_list (list, initial value: []): Array that stores the positions of the points found by the laser. The points are given with respect to the location of the sensor, and stored as lists of three elements. The number of points depends on the geometry of the arc parented to the sensor (see below). The point (0, 0, 0) means that this ray has not it anything in its range
  • range_list (list, initial value: []): Array that stores the distance to the first obstacle detected by each ray. The order indexing of this array is the same as for point_list, so that the element in the same index of both lists will correspond to the measures for the same ray. If the ray does not hit anything in its range it returns laser_range
  • remission_list (list, initial value: []): Array that stores the remission value for the points found by the laser. The specular intensity is set as the remission value. If no object is hit, the remission value is set to 0

  Interface support:

  • socket as straight JSON serialization (morse.middleware.socket_datastream.SocketPublisher)

Services for Laser Scanner Sensors

• get_configurations() (blocking)

  Returns the configurations of a component (parsed from the properties).

  • Return value

    a dictionary of the current component’s configurations

• get_local_data() (blocking)

  Returns the current data stored in the sensor.

  • Return value

    a dictionary of the current sensor’s data

• get_properties() (blocking)

  Returns the properties of a component.

  • Return value

    a dictionary of the current component’s properties

• set_property(prop_name, prop_val) (blocking)

  Modify one property on a component

  • Parameters

    • prop_name: the name of the property to modify (as shown the documentation)
    • prop_val: the new value of the property. Note that there is no checking about the type of the value so be careful

  • Return value

    nothing

Examples

The following examples show how to use this component in a Builder script:

from morse.builder import *

# adds a default robot (the MORSE mascott!)
robot = Morsy()

# creates a new instance of the sensor
laserscanner = LaserScanner()

# place your component at the correct location
laserscanner.translate(<x>, <y>, <z>)
laserscanner.rotate(<rx>, <ry>, <rz>)

# select a specific abstraction level (cf below), or skip it to use default level
laserscanner.level(<level>)

robot.append(laserscanner)

# define one or several communication interface, like 'socket'
laserscanner.add_interface(<interface>)

env = Environment('empty')

Other sources of examples

• Source code
• Unit-test

(This page has been auto-generated from MORSE module morse.sensors.laserscanner.)