Laser range scanners

This is a whole collection of sensors that 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

../../_images/sick.png

SICK LMS500

../../_images/sick-ld-mrs.png

SICK LD-MRS

../../_images/hokuyo.png

Hokuyo

 

Files

There are a few different Blender files available for this type of sensor, with meshes representing various models of laser range scanners. They all use the same Python script for their behaviour.

  • Blender: $MORSE_ROOT/data/sensors/sick.blend, $MORSE_ROOT/data/sensors/sick-ld-mrs.blend, $MORSE_ROOT/data/sensors/hokuyo.blend
  • Python: $MORSE_ROOT/src/morse/sensors/sick.py

Local data

  • point_list: (list array) 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).
  • range_list: (float array) 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.

Configurable Parameters

The Empty object corresponding to this sensor has the following parameters in the Logic Editor panel:

  • Visible_arc: (Boolean) A toggle that determines whether the scanned area is displayed during the execution of the simulation or not (Default: False). If the robot is also equipped with a camera, it is better to set this variable to False, otherwise the scanned area will also appear on the captured images.
  • laser_range: (Float) The distance in meters from the center of the sensor to which it is capable of detecting other objects.
  • resolution: (Float) 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) The full angle covered by the sensor. Expressed in degrees in decimal format. Used when creating the arc object.

The following parameters are optional. Mainly used to create multiple scanning layers, as is the case for the SICK LD-MRS sensor:

  • layers: (Integer) Number of scanning planes used by the sensor.
  • layer_separation: (Float) The angular separation between the planes. Must be given in degrees.
  • layer_offset: (Float) The horizontal distance between the scan points in consecutive scanning layers. Must be given in degrees.

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.

By default, the SICK has an arc that spans 180 degrees, with a resolution of 1 degree. This can be changed using a special method in the Builder API, which can create any arc of the desired geometry. The shape of the arc is determined from the parameters of resolution and scan_window specified as game properties of the Sick sensor. The name of the method is create_sick_arc, and must be called after setting the desired value for the previously mentioned properties.

An example of how to change the arc object using the Builder API is show below:

from morse.builder.morsebuilder import *

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

An example for creating a properly configured SICK LD-MRS is given below:

from morse.builder.morsebuilder import *

sick = Sensor('sick-ld-mrs')
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)
sick.create_sick_arc()

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)

Table Of Contents

Previous topic

Semantic camera sensor

Next topic

Stereo Camera unit

This Page