JTS: generate a polygon geometry from line geomtry

Question

I have a line and I wish to convert it to a polygon.
The point is this line is NOT a ring it's an straight Line. And I want to use an specific width to extend line horizontally and create a polygon.

Using JTS. is it possible? How can I make it happen?

Answer 1

Since you want a simple horizontal offset this is quite easy, you need to reverse the order of the points and then add each one in turn with the x offset applied and create a polygon from the linestring.

package spike;

import java.util.ArrayList;
import java.util.Arrays;

import org.apache.commons.lang.ArrayUtils;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.LineString;
import org.locationtech.jts.geom.Polygon;

public class LineToPoly {
  static GeometryFactory gf = new GeometryFactory();

  public static void main(String[] args) {
    Coordinate[] points = {new Coordinate(10000,10000),new Coordinate(12300,40000),new Coordinate(16800,50000),new Coordinate(12354,60000)};
    LineString line = gf.createLineString(points );

    double offset = 1000; //1km
    System.out.println(line);
    Polygon p = generatePoly(line,offset);
    System.out.println(p);
  }

  private static Polygon generatePoly(LineString line, double offset) {

    Coordinate[] points = line.getCoordinates();

    ArrayList<Coordinate> soln = new ArrayList<>();
    //store initial points
    soln.addAll(Arrays.asList(points));
    // reverse the list
    ArrayUtils.reverse(points);
    // for each point move offset metres right 
    for (Coordinate c:points) {
      soln.add(new Coordinate(c.x+offset, c.y));
    }
    // close the polygon
    soln.add(soln.get(0));
    // create polygon
    Polygon poly = gf.createPolygon(soln.toArray(new Coordinate[] {}));
    return poly;
  }

}

This gives the following:

LINESTRING (10000 10000, 12300 40000, 16800 50000, 12354 60000)
POLYGON ((10000 10000, 12300 40000, 16800 50000, 12354 60000, 13354 60000, 17800 50000, 13300 40000, 11000 10000, 10000 10000))