Overview

The non persistent voxel layer incorporate information from the sensors in the form of PointClouds or LaserScans. This information is converted into 3D and populated into a temporary voxel_grid for each sensor cycle.

ROS drop in replacement to the voxel layer which does not persist readings through iterations when ray tracing or map maintenance is undesirable.

Created in response to need for a rolling local costmap layer to not persist readings due to a specific sensor being used. After looking through the community, it seems several people on ros answers have asked for a similar tool. This is to make that possible.

Source and bug tracker: https://github.com/SteveMacenski/nonpersistent_voxel_layer

Maintainer: Steve Macenski <stevenmacenski AT gmail DOT com>

Author: Steve Macenski, based on work from: Eitan Marder-Eppstein, David V. Lu!!, Dave Hershberger, contradict@gmail.com

Marking

The costmap automatically subscribes to sensors topics and updates itself accordingly. Each sensor is used to mark. With the voxel layer, obstacle information from each column is projected down into two dimensions when put into the costmap. The non-persistent voxel layer does not do any clearing and resets each sensor cycle.

ROS API

Same API applies to this layer as to the voxel layer, except for the clearing operations.

Subscribed Topics

<point_cloud_topic> (sensor_msgs/PointCloud)

• For each "PointCloud" source listed in the observation_sources parameter list, information from that source is used to update the costmap.

<point_cloud2_topic> (sensor_msgs/PointCloud2)

• For each "PointCloud2" source listed in the observation_sources parameter list, information from that source is used to update the costmap.

<laser_scan_topic> (sensor_msgs/LaserScan)

• For each "LaserScan" source listed in the observation_sources parameter list, information from that source is used to update the costmap.

"map" (nav_msgs/OccupancyGrid)

• The costmap has the option of being initialized from a user-generated static map (see the static_map parameter). If this option is selected, the costmap makes a service call to the map_server to obtain this map.

Sensor management parameters

~<name>/observation_sources (string, default: "")

• A list of observation source names separated by spaces. This defines each of the <source_name> namespaces defined below.

Each source_name in observation_sources defines a namespace in which parameters can be set:

~<name>/<source_name>/topic (string, default: source_name)

• The topic on which sensor data comes in for this source. Defaults to the name of the source.

~<name>/<source_name>/sensor_frame (string, default: "")

• The frame of the origin of the sensor. Leave empty to attempt to read the frame from sensor data. The frame can be read from both sensor_msgs/LaserScan, sensor_msgs/PointCloud, and sensor_msgs/PointCloud2 messages.

~<name>/<source_name>/observation_persistence (double, default: 0.0)

• How long to keep each sensor reading in seconds. A value of 0.0 will only keep the most recent reading.

~<name>/<source_name>/expected_update_rate (double, default: 0.0)

• How often to expect a reading from a sensor in seconds. A value of 0.0 will allow infinite time between readings. This parameter is used as a failsafe to keep the navigation stack from commanding the robot when a sensor has failed. It should be set to a value that is slightly more permissive than the actual rate of the sensor. For example, if we expect a scan from a laser every 0.05 seconds we might set this parameter to be 0.1 seconds to give a generous buffer and account for some amount of system latency.

~<name>/<source_name>/data_type (string, default: "PointCloud")

• The data type associated with the topic, right now only "PointCloud", "PointCloud2", and "LaserScan" are supported.

~<name>/<source_name>/marking (bool, default: true)

• Whether or not this observation should be used to mark obstacles.

~<name>/<source_name>/max_obstacle_height (double, default: 2.0)

• The maximum height in meters of a sensor reading considered valid. This is usually set to be slightly higher than the height of the robot. Setting this parameter to a value greater than the global max_obstacle_height parameter has no effect. Setting this parameter to a value less than the global max_obstacle_height will filter out points from this sensor above that height.

~<name>/<source_name>/min_obstacle_height (double, default: 0.0)

• The minimum height in meters of a sensor reading considered valid. This is usually set to be at ground height, but can be set higher or lower based on the noise model of your sensor.

~<name>/<source_name>/obstacle_range (double, default: 2.5)

• The maximum range in meters at which to insert obstacles into the costmap using sensor data.

~<name>/<source_name>/raytrace_range (double, default: 3.0)

• The maximum range in meters at which to raytrace out obstacles from the map using sensor data.

~<name>/<source_name>/inf_is_valid (bool, default: false)

• Allows for Inf values in "LaserScan" observation messages. The Inf values are converted to the laser maximum range.

Global Filtering Parameters

These parameters apply to all sensors.

~<name>/max_obstacle_height (double, default: 2.0)

• The maximum height of any obstacle to be inserted into the costmap in meters. This parameter should be set to be slightly higher than the height of your robot.

~<name>/obstacle_range (double, default: 2.5)

• The default maximum distance from the robot at which an obstacle will be inserted into the cost map in meters. This can be over-ridden on a per-sensor basis.

NonPersistentVoxelCostmapPlugin

The following parameters are used by the NonPersistentVoxelCostmapPlugin.

~<name>/origin_z (double, default: 0.0)

• The z origin of the map in meters.

~<name>/z_resolution (double, default: 0.2)

• The z resolution of the map in meters/cell.

~<name>/z_voxels (int, default: 10)

• The number of voxels to in each vertical column, the height of the grid is z_resolution * z_voxels.

~<name>/unknown_threshold (int, default: ~<name>/z_voxels)

• The number of unknown cells allowed in a column considered to be "known"

~<name>/mark_threshold (int, default: 0)

• The maximum number of marked cells allowed in a column considered to be "free".

~<name>/publish_voxel_map (bool, default: false)

• Whether or not to publish the underlying voxel grid for visualization purposes.

~<name>/footprint_clearing_enabled (bool, default: true)

• If true, the robot footprint will clear (mark as free) the space in which it travels.