polygon-contains-point

The point-in-polygon (PIP) problem asks whether a given point in the plane lies inside, outside, or on the boundary of a polygon. Wiki reference: Point in polygon

Algorithm

The number of intersections for a ray passing from the exterior of the polygon to any point; if odd, it shows that the point lies inside the polygon. If it is even, the point lies outside the polygon.

Usage

Build Polygon

This is the simple version of the polygon. You can build both types of polygons: concave and non-convex

Polygon polygon = Polygon.Builder()
        .addVertex(new Point(1, 3))
        .addVertex(new Point(2, 8))
        .addVertex(new Point(5, 4))
        .addVertex(new Point(5, 9))
        .addVertex(new Point(7, 5))
        .addVertex(new Point(6, 1))
        .addVertex(new Point(3, 1))
        .build();

Build Polygon with Holes

First build all the border sides of the polygon. Close the borders and then you can start adding holes into the polygon. You can add multiple number of holes, just remember to close() after each added hole.

Polygon polygon = Polygon.Builder()
        .addVertex(new Point(1, 2)) // polygon
        .addVertex(new Point(1, 6))
        .addVertex(new Point(8, 7))
        .addVertex(new Point(8, 1))
        .close() 
        .addVertex(new Point(2, 3)) // hole one
        .addVertex(new Point(5, 5))
        .addVertex(new Point(6, 2))
        .close() 
        .addVertex(new Point(6, 6)) // hole two
        .addVertex(new Point(7, 6))
        .addVertex(new Point(7, 5))
        .build();

Check if the point inside

Point point = new Point(4.5f, 7);
boolean contains = polygon.contains(point);

Tests

Two main tests are attached (not in junit format). Both tests cover polygons with holes and without.

License

Copyright 2013-present Roman Kushnarenko

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

adamjoniec / polygon-contains-point