polygon_ros

Messages and libraries for operating on two dimensional polygons.

In the standard package geometry_msgs, Polygon.msg and PolygonStamped.msg are defined, but have three primary limitations.

• The Polygon is defined by Point32 which uses float32 limited precision to store the coordinates.
• The point is also defined in three dimensions, leading to an often ignored Z coordinate.
• There is no support for complex polygons i.e. polygons with holes in them.

This led to the creation of the new messages defined in this package. This work is forked from the ROS 1 version of the robot_navigation.

Data Types

• The base datatype is Point2D, which defines an x and a y coordinate, in 64 bit precision.
• The Polygon2D type defines a simple polygon with an ordered list of Point2D that are the vertices of the polygon. The first point is connected to the second, the second is connected to the third, and so on, and the last point is also connected to the first.
• Polygon2DStamped is a single simple polygon with a header.
• ComplexPolygon2D defines a complex polygon with one polygon that is the outer perimeter, and an arbitrary number of polygons that define the holes.
• Polygon2DCollection is a list of simple polygons, all with the same frame. There is also an optional per-polygon colors field for display purposes.
• Similarly, ComplexPolygon2DCollection is a list of complex polygons, also with a header, and an optional colors field.

Polygon Utils

The polygon_utils package provides a number of tools for working with polygon_msgs.

Conversions

Note that when converting from geometry_msgs to polygon_msgs, any information in the z coordinate is discarded.

Operations

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

Python

There are also a few Python-based utility operations available.

• polygon_utils.shapely_lib.py provides conversions from ROS messages to Shapely objects, enabling a large library of algorithms to be run. Note: Requires shapely to be installed via pip.
• polygon_utils.shortest_path.py provides methods for determining the shortest path around a collection of polygons. (also uses shapely_lib)

RViz Plugins

The existing rviz_default_plugins::PolygonDisplay draws only the outline of a given polygon, and cannot fill the polygon in with color. This package has five new RViz displays for polygon data:

• polygon_rviz_plugins::Polygon3DDisplay will display geometry_msgs/PolygonStamped messages just like rviz_default_plugins::PolygonDisplay except it can fill in the polygon.
• polygon_rviz_plugins::PolygonDisplay displays polygon_msgs/Polygon2DStamped messages
• polygon_rviz_plugins::ComplexPolygonDisplay displays polygon_msgs/ComplexPolygon2DStamped messages
• polygon_rviz_plugins::PolygonsDisplay (note the S in PolygonS) will display polygon_msgs/Polygon2DCollection messages.
• polygon_rviz_plugins::ComplexPolygonsDisplay (note the S in PolygonS) will display polygon_msgs/ComplexPolygon2DCollection messages.

Each has three display modes, for displaying just the outline, just the filler, or both.

When displaying polygon collections, you have the option to display a single color, colors from the message, or a set of “unique” colors (limited to 54 colors).

The behavior is showcased by running ros2 launch polygon_demos polygons.launch.py. The results are also shown in the screenshot above.

• The blue star in the middle is a Polygon2DStamped
• The white star is a geometry_msgs/PolygonStamped
• The star burst around the white star is a ComplexPolygon2DStamped
• The ring of yellow stars is a Polygon2DCollection
• The rainbow-colored stars around the blue star are a ComplexPolygon2DCollection