Line between outside and inside polygon - geotools

Question

I have two polygons, one inside another, and one draw it on the map there is a line connecting vertices of outside and inside polygon. I am trying to draw it like multipolygon using

Polygon[] polygons = null;
List<Polygon> PolygonList = new ArrayList<Polygon>();
polygons = new Polygon[PolygonList.size()];
PolygonList.toArray(polygons);
MultiPolygon multiPolygon = null;
multiPolygon = geometryFactory.createMultiPolygon(polygons);

Original coordinates stored in PolygonList and then converted in polygon array are,

[POLYGON ((6420562.64 4963523.59, 6420559.63 4963527.13, 6420551.28 4963536.4, 6420545.66 4963542.93, 6420539.47 4963549.81, 6420549.2 4963566.43, 6420557.44 4963581.87, 6420547.09 4963592.12, 6420546.75 4963592.47, 6420538.87 4963604.54, 6420542.3 4963606.54, 6420554.08 4963592.16, 6420569.13 4963585.65, 6420581.56 4963580.36, 6420579.2 4963571.27, 6420577.81 4963568, 6420576.04 4963565.49, 6420573.62 4963563.02, 6420569.94 4963560.08, 6420564.25 4963556.37, 6420556.16 4963551.2, 6420552.46 4963548.07, 6420551.29 4963549.4, 6420549.14 4963547.81, 6420552.7 4963543.31, 6420554.96 4963544.66, 6420559.37 4963535.02, 6420556.44 4963532.82, 6420560.19 4963527.58, 6420563.24 4963529.58, 6420564.47 4963526.17, 6420562.64 4963523.59)), POLYGON ((6420560.94 4963584.49, 6420567.53 4963579.99, 6420563.58 4963574.11, 6420557.04 4963578.61, 6420560.94 4963584.49))]

but when I get coordinates from created multipolygon all coordinates are mixed,

[(6420562.64, 4963523.59, NaN), (6420559.63, 4963527.13, NaN), (6420551.28, 4963536.4, NaN), (6420545.66, 4963542.93, NaN), (6420539.47, 4963549.81, NaN), (6420549.2, 4963566.43, NaN), (6420557.44, 4963581.87, NaN), (6420547.09, 4963592.12, NaN), (6420546.75, 4963592.47, NaN), (6420538.87, 4963604.54, NaN), (6420542.3, 4963606.54, NaN), (6420554.08, 4963592.16, NaN), (6420569.13, 4963585.65, NaN), (6420581.56, 4963580.36, NaN), (6420579.2, 4963571.27, NaN), (6420577.81, 4963568.0, NaN), (6420576.04, 4963565.49, NaN), (6420573.62, 4963563.02, NaN), (6420569.94, 4963560.08, NaN), (6420564.25, 4963556.37, NaN), (6420556.16, 4963551.2, NaN), (6420552.46, 4963548.07, NaN), (6420551.29, 4963549.4, NaN), (6420549.14, 4963547.81, NaN), (6420552.7, 4963543.31, NaN), (6420554.96, 4963544.66, NaN), (6420559.37, 4963535.02, NaN), (6420556.44, 4963532.82, NaN), (6420560.19, 4963527.58, NaN), (6420563.24, 4963529.58, NaN), (6420564.47, 4963526.17, NaN), (6420562.64, 4963523.59, NaN)]

and the drawn polygon look like this enter image description here (image is rotated) Is there any way to use multipolygon or need to use a linear ring and define polygon with holes in it.

Answer 1

The problem is (as you discovered) that you don't want a multipolygon at all, you want a single polygon with a hole in it. This is how you would create one of those:

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.GeometryFactory;
import com.vividsolutions.jts.geom.LinearRing;
import com.vividsolutions.jts.geom.Polygon;

public class Holes {
  /**
   * build a polygon with a hole in it.
   * 
   * @param args
   */
  public static void main(String[] args) {
    GeometryFactory gf = new GeometryFactory();
    // coords for outer ring & hole
    String[] coords = {
        "6420562.64 4963523.59, 6420559.63 4963527.13, 6420551.28 4963536.4, 6420545.66 4963542.93, 6420539.47 4963549.81, 6420549.2 4963566.43, 6420557.44 4963581.87, 6420547.09 4963592.12, 6420546.75 4963592.47, 6420538.87 4963604.54, 6420542.3 4963606.54, 6420554.08 4963592.16, 6420569.13 4963585.65, 6420581.56 4963580.36, 6420579.2 4963571.27, 6420577.81 4963568, 6420576.04 4963565.49, 6420573.62 4963563.02, 6420569.94 4963560.08, 6420564.25 4963556.37, 6420556.16 4963551.2, 6420552.46 4963548.07, 6420551.29 4963549.4, 6420549.14 4963547.81, 6420552.7 4963543.31, 6420554.96 4963544.66, 6420559.37 4963535.02, 6420556.44 4963532.82, 6420560.19 4963527.58, 6420563.24 4963529.58, 6420564.47 4963526.17, 6420562.64 4963523.59",
        "6420560.94 4963584.49, 6420567.53 4963579.99, 6420563.58 4963574.11, 6420557.04 4963578.61, 6420560.94 4963584.49" };

    Coordinate[] c = convertToCoords(coords[0]);
    LinearRing outer = gf.createLinearRing(c);
    LinearRing[] inners = new LinearRing[1];
    inners[0] = gf.createLinearRing(convertToCoords(coords[1]));

    Polygon out = gf.createPolygon(outer, inners);
    System.out.println(out);
  }

  /**
   * @param coords
   * @return
   */
  public static Coordinate[] convertToCoords(String coords) {
    String[] pairs = coords.split(",");

    Coordinate[] c = new Coordinate[pairs.length];
    int i = 0;
    for (String p : pairs) {
      String[] xy = p.trim().split("  *");
      c[i++] = new Coordinate(Double.parseDouble(xy[0]), Double.parseDouble(xy[1]));
    }
    return c;
  }

}

This gives you the following WKT:

POLYGON ((6420562.64 4963523.59, 6420559.63 4963527.13, 6420551.28 4963536.4, 6420545.66 4963542.93, 6420539.47 4963549.81, 6420549.2 4963566.43, 6420557.44 4963581.87, 6420547.09 4963592.12, 6420546.75 4963592.47, 6420538.87 4963604.54, 6420542.3 4963606.54, 6420554.08 4963592.16, 6420569.13 4963585.65, 6420581.56 4963580.36, 6420579.2 4963571.27, 6420577.81 4963568, 6420576.04 4963565.49, 6420573.62 4963563.02, 6420569.94 4963560.08, 6420564.25 4963556.37, 6420556.16 4963551.2, 6420552.46 4963548.07, 6420551.29 4963549.4, 6420549.14 4963547.81, 6420552.7 4963543.31, 6420554.96 4963544.66, 6420559.37 4963535.02, 6420556.44 4963532.82, 6420560.19 4963527.58, 6420563.24 4963529.58, 6420564.47 4963526.17, 6420562.64 4963523.59), (6420560.94 4963584.49, 6420567.53 4963579.99, 6420563.58 4963574.11, 6420557.04 4963578.61, 6420560.94 4963584.49))