Collision Detector Node¶
+The Collision Detector is a node similar to the Collision Monitor, so it is recommended to read the Using Collision Monitor tutorial first.
+In some cases, the user may want to be informed about the detected obstacles without affecting the robot’s velocity and instead take a different action within an external node. For example, the user may want to blink LEDs or sound an alarm when the robot is close to an obstacle.
+Another use case could be to detect data points in particular regions (e.g extremely close to the sensor) and warn of malfunctioning sensors. For this purpose, the Collision Detector node was introduced.
+It works similarly to the Collision Monitor, but does not affect the robot’s velocity. It will only inform that data from the configured sources has been detected within the configured polygons via message to the collision_detector_state topic.
See the package’s README for more information.
Features¶
+Similarly to the Collision Monitor, the Collision Detector uses robot’s relative polygons to define “zones”. +However, unlike the Collision Monitor that uses different behavior models, the Collision Detector does not use any of them and therefore the action_type should always be set to none. If set to anything else, it will throw an error
+The zones around the robot and the data sources are the same as for the Collision Monitor, with the exception of the footprint polygon, which is not supported by the Collision Detector.
+Parameters¶
+-
+
- frequency +
+
++ + ++ + Type
Default
double
10.0
-
+
- Description:
Frequency of the main loop that checks for detections.
+
+
+- base_frame_id +
+
++ + ++ + Type
Default
string
“base_footprint”
-
+
- Description:
Robot base frame.
+
+
+- odom_frame_id +
+
++ + ++ + Type
Default
string
“odom”
-
+
- Description:
Which frame to use for odometry.
+
+
+- transform_tolerance +
+
++ + ++ + Type
Default
double
0.1
-
+
- Description
Time with which to post-date the transform that is published, to indicate that this transform is valid into the future.
+
+
+- source_timeout +
+
++ + ++ + Type
Default
double
2.0
-
+
- Description:
Maximum time interval in which source data is considered as valid.
+
+
+- base_shift_correction +
+
++ + ++ + Type
Default
bool
True
-
+
- Description:
Whether to correct source data towards to base frame movement, considering the difference between current time and latest source time. If enabled, produces more accurate sources positioning in the robot base frame, at the cost of slower performance. This will cause average delays for
+~1/(2*odom_rate)per eachcmd_velcalculation cycle. However, disabling this option for better performance is not recommended for the fast moving robots, where during the typical rate of data sources, robot could move unacceptably far. Thus reasonable odometry rates are recommended (~100 hz).
+
+- polygons +
+
++ + ++ + Type
Default
vector<string>
N/A
-
+
- Description:
List of zones to check for data points. Causes an error, if not specialized.
+
+
+- observation_sources +
+
++ + ++ + Type
Default
vector<string>
N/A
-
+
- Description:
List of data sources (laser scanners, pointclouds, etc…). Causes an error, if not specialized.
+
+
+
Polygons parameters¶
+<polygon name> is the corresponding polygon name ID selected for this type.
-
+
<polygon_name>.type
++
++ + ++ + Type
Default
string
N/A
-
+
- Description:
Type of polygon shape. Available values are
+polygon,circle. Causes an error, if not specialized.
+
+<polygon_name>.points
++
++ + ++ + Type
Default
vector<double>
N/A
-
+
- Description:
Polygon vertexes, listed in
+{p1.x, p1.y, p2.x, p2.y, p3.x, p3.y, ...}format (e.g.{0.5, 0.25, 0.5, -0.25, 0.0, -0.25, 0.0, 0.25}for the square in the front). Used forpolygontype. Minimum 3 points for a triangle polygon. If not specified, the collision detector will use dynamic polygon subscription topolygon_sub_topic
+
+<polygon_name>.polygon_sub_topic
++
++ + ++ + Type
Default
string
N/A
-
+
- Description:
Topic to listen the polygon points from. Causes an error, if not specified and points are also not specified. If both
+pointsandpolygon_sub_topicare specified, the staticpointstakes priority.
+
+<polygon_name>.radius
++
++ + ++ + Type
Default
double
N/A
-
+
- Description:
Circle radius. Used for
+circletype. Causes an error, if not specialized.
+
+<polygon_name>.action_type
++
++ + ++ + Type
Default
string
N/A
-
+
- Description:
Only
+noneaction type is supported (more options available for collision monitor)
+
+<polygon_name>.min_points
++
++ + ++ + Type
Default
int
4
-
+
- Description:
Minimum number of data readings within a zone to trigger the action. Former
+max_pointsparameter for Humble, that meant the maximum number of data readings within a zone to not trigger the action).min_pointsis equal tomax_points + 1value.
+
+<polygon_name>.visualize
++
++ + ++ + Type
Default
bool
False
-
+
- Description:
Whether to publish the polygon in a separate topic.
+
+
+<polygon_name>.polygon_pub_topic
++
++ + ++ + Type
Default
string
<polygon_name>
-
+
- Description:
Topic name to publish a polygon to. Used only if
+visualizeis true.
+
+
Observation sources parameters¶
+<source name> is the corresponding data source name ID selected for this type.
-
+
<source name>.type
++
++ + ++ + Type
Default
string
“scan”
-
+
- Description:
Type of polygon shape. Could be
+scan,pointcloudorrange.
+
+<source name>.topic
++
++ + ++ + Type
Default
string
“scan”
-
+
- Description:
Topic to listen the source data from.
+
+
+<source name>.min_height
++
++ + ++ + Type
Default
double
0.05
-
+
- Description:
Minimum height the PointCloud projection to 2D space started from. Applicable for
+pointcloudtype.
+
+<source name>.max_height
++
++ + ++ + Type
Default
double
0.5
-
+
- Description:
Maximum height the PointCloud projection to 2D space ended with. Applicable for
+pointcloudtype.
+
+<source name>.obstacles_angle
++
++ + ++ + Type
Default
double
PI / 180 (1 degree)
-
+
- Description:
Angle increment (in radians) between nearby obstacle points at the range arc. Two outermost points from the field of view are not taken into account (they will always exist regardless of this value). Applicable for
+rangetype.
+
+
Example¶
+Here is an example of configuration YAML for the Collision Detector.
+collision_detector:
+ ros__parameters:
+ base_frame_id: "base_footprint"
+ odom_frame_id: "odom"
+ transform_tolerance: 0.5
+ source_timeout: 5.0
+ base_shift_correction: True
+ polygons: ["PolygonFront"]
+ PolygonFront:
+ type: "polygon"
+ points: [0.3, 0.3, 0.3, -0.3, 0.0, -0.3, 0.0, 0.3]
+ action_type: "none"
+ min_points: 4
+ visualize: True
+ polygon_pub_topic: "polygon_front"
+ observation_sources: ["scan"]
+ scan:
+ type: "scan"
+ topic: "scan"
+ pointcloud:
+ type: "pointcloud"
+ topic: "/intel_realsense_r200_depth/points"
+ min_height: 0.1
+ max_height: 0.5
+