java - How to calculate the distance in meters between a geographic point and a given polygon? -

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first of all, i'm new gis, pardon mistakes. need discover distance between latitude , longitude point , latitude/longitude polygon (regular or not). precisely, need discover minimal distance given point point in polygon's boundary, illustrated below. in example, closer distance point p polygon d. note: don't need point, minimum distance.

problem illustration

after reading, i've come following minimum working example using geotools api. however, think i'm messing in output. can enlight me on how minimum distance between point , polygon in mteres?

mwe.java:

import com.vividsolutions.jts.geom.coordinate; import com.vividsolutions.jts.geom.geometry; import com.vividsolutions.jts.geom.geometryfactory; import com.vividsolutions.jts.geom.point;  public class mwe {      public static void main(string[] args) throws exception {         geometryfactory gf = jtsfactoryfinder.getgeometryfactory();          coordinate[] c = new coordinate[5];         c[0] = new coordinate(-49.242986, -16.662430);         c[1] = new coordinate(-49.241999, -16.664465);         c[2] = new coordinate(-49.239146, -16.663828);         c[3] = new coordinate(-49.239832, -16.661443);         c[4] = new coordinate(-49.242986, -16.662430);          geometry geo = gf.createpolygon(c);          point p = gf.createpoint(new coordinate(-49.246870, -16.665493));          double distance = geo.distance(p);          system.out.println("distance: " + distance);      } }

so doing correct, return distance in geodetic units (degrees of arc) rather metres. have 2 options:

  1. transform point , polygon geometries planar reference system http://docs.geotools.org/latest/tutorials/geometry/geometrycrs.html
  2. use geodeticcalculator http://docs.geotools.org/stable/userguide/library/referencing/calculator.html

to use geodeticcalculator need determine closest point on polygon boundary point. e.g. distanceop.closestpoints(geo, p)[0]

// adapted http://docs.geotools.org/stable/userguide/library/referencing/calculator.html coordinatereferencesystem crs = crs.decode("epsg:4326"); geodeticcalculator gc = new geodeticcalculator(crs); gc.setstartingposition( jts.todirectposition(  distanceop.closestpoints(geo, p)[0], crs ) ); gc.setdestinationposition( jts.todirectposition( p, crs ) );  double distance = gc.getorthodromicdistance();

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