mir_amr/navigations/nav_2d_utils/doc/PolygonsAndFootprints.md

nav_2d_utils Polygons and Footprints

This library represents a replacement for costmap_2d/footprint.h and deals with manipulating polygons. Note that implicitly all polygons here are assumed to be simple polygons without "holes."

Polygons and the Parameter Server

There have historically been three primary ways to specify a polygon/footprint on the parameter server. The first is to simply specify a radius which is converted to a hexadecagon, i.e. polygon with sixteen sides. This can be read with

nav_2d_msgs::Polygon2D polygonFromRadius(const double radius, const unsigned int num_points = 16);

The second two ways involve specifying the points of the polygon individually. This can be done with either a string representing a bracketed array of arrays of doubles, "[[1.0, 2.2], [3.3, 4.2], ...]". This can be read with

nav_2d_msgs::Polygon2D polygonFromString(const std::string& polygon_string);

Alternatively, with ROS, you can read the points directly from the parameter server in the form of an XmlRpcValue, which should be an array of arrays of doubles, which is read with

nav_2d_msgs::Polygon2D polygonFromXMLRPC(XmlRpc::XmlRpcValue& polygon_xmlrpc);

If the XmlRpcValue is a string, it will call the polygonFromString method.

The above are the traditional methods that were supported by the original costmap_2d code. However, we add a fourth method that requires two parallel arrays of x and y coordinates.

nav_2d_msgs::Polygon2D polygonFromParallelArrays(const std::vector<double>& xs, const std::vector<double>& ys);

All of the above methods (except the radius one) can be loaded as appropriate from the parameter server with

nav_2d_msgs::Polygon2D polygonFromParams(const ros::NodeHandle& nh, const std::string parameter_name,
                                         bool search = true);

to include the radius, use the logic in footprint.h which either uses "footprint" or "robot_radius"

nav_2d_msgs::Polygon2D footprintFromParams(ros::NodeHandle& nh, bool write = true);

Polygons can be written to parameters with

void polygontoParams(const nav_2d_msgs::Polygon2D& polygon, const ros::NodeHandle& nh, const std::string parameter_name,
                     bool array_of_arrays = true);

Polygon Operations

There are also a handful of methods for examining/manipulating polygons

• equals - check if two polygons are equal
• movePolygonToPose - translate and rotate a polygon
• isInside - check if a point is inside a polygon
• calculateMinAndMaxDistances - Calculate the minimum and maximum distance from the origin of a polygon
• triangulate - Decompose a polygon into a set of non-overlapping triangles using an open source implementation of the earcut algorithm