Check the a Point (Latitude, Longitude) inside Or Outside the Polygon

Question

Let us consider a Polygon (P) with N points each points are represented with Latitude and Longitude. Now I would like to check a new point P1 (latitude and longitude) is Inside/ Outside the Polygon??

Answer 1

Point within polygon test is a common algorithm that is implemented in many geospatial libraries in different programming languages.

JTS Topology Suite, for example, is a robust open source API of 2D spatial predicates and functions in Java. It provides the methods to test if a geometry (e.g. Point) is contained within another geometry (e.g. Polygon).

Here is a code snippet:

doube lat = ....; // latitude in decimal degrees
double lon = ...; // longitude in decimal degrees
Coordinate[] points = ... // construct/initialize points for polygon

// now construct the polygon and test the point
GeometryFactory gf = new GeometryFactory();
LinearRing jtsRing = gf.createLinearRing(points);
Polygon poly = gf.createPolygon(jtsRing, null);
Coordinate coord = new Coordinate(lon, lat);
Point pt = gf.createPoint(coord);
if (poly.contains(pt)) {
  // point is contained within polygon
} else {
  // point is NOT contained within polygon
}

The contains() geometry predicate is defined in the JTS javadoc.

See also JTS project on github