find nearest point (geometry point)

Question

I want to compute the nearest point from a starting point (reference) when I have geometry point.

I am using the ports.shp file for this reason.

The code works most of the time.But sometimes it returns null minDistPoint is null. I am not sure with what value to initialize minDist.

public Point findNearestPoint( Point p, SimpleFeatureCollection features ) throws FactoryException, TransformException {
   Point destination = null;
   double minDist = 10.0e+6;
   double distance = 0;
   Point minDistPoint = null;
   try( SimpleFeatureIterator itr = features.features()) {
      while( itr.hasNext()) {
         SimpleFeature feature = itr.next();
         final String EPSG4326 =
            "GEOGCS[\"WGS 84\",DATUM[\"WGS_1984\","+
            "SPHEROID[\"WGS 84\",6378137,298.257223563,"+
            "AUTHORITY[\"EPSG\",\"7030\"]],"+
            "AUTHORITY[\"EPSG\",\"6326\"]]," + 
            "PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],"+
            "UNIT[\"degree\", " +"0.01745329251994328,"+
            "AUTHORITY[\"EPSG\",\"9122\"]],"+
            "AUTHORITY[\"EPSG\",\"4326\"]]";
         CoordinateReferenceSystem crs = CRS.parseWKT(EPSG4326);    
         destination = (Point) feature.getDefaultGeometry(); 
         GeodeticCalculator gc = new GeodeticCalculator(crs); 
         gc.setStartingPosition(
            JTS.toDirectPosition( p.getCoordinate(), crs));
         gc.setDestinationPosition(
            JTS.toDirectPosition( dest.getCoordinate(), crs));
         distance = gc.getOrthodromicDistance();
         if( distance < minDist ) {
            minDist = distance;
            minDistPoint = destination;
            lastMatched = feature;
         }
      }
   }
   int totalmeters = (int) minDist;
   int km = totalmeters / 1000;
   int meters = totalmeters - (km * 1000);
   float remaining_cm = (float) (minDist - totalmeters) * 10000;
   remaining_cm = Math.round(remaining_cm);
   float cm = remaining_cm / 100;
   System.out.println(
      "Distance = " + km + "km " + meters + "m " + cm + "cm");
   if( minDistPoint == null ) {
      return null;
   }
   return minDistPoint;
}

you can try with `Double.POSITIVE_INFINITY`, which will allow you to assure that at least the first time the `if` condition will be true. — bracco23, Jul 25 '17 at 09:25
@bracco23:It seems to work fine, thanks!Make it an answer please. — George, Jul 25 '17 at 09:55

score 1 · Accepted Answer · answered Jul 25 '17 at 09:59

With every algorithm to find the minimum, you should always set the initial value to either the first one of the set or the maximum value achievable.

In your case, since you are using a double, you can use Double.POSITIVE_INFINITY as initial value, this will allow you to assure that at least the first time the if condition will be true.

score 0 · Answer 2 · answered Jul 25 '17 at 10:01

0

The computer science answer was given in a comment, Double.PositiveInfinity is bigger than any number. The geospatial answer is that on a sphere no two points are more than pi*r apart. For planet earth a goood upper bound would be 3.14*6400 km. Use positive infinity.

answered Jul 25 '17 at 10:01

Meir Maor

1,200
8
18

2 * pi * R is the circumference, the maximum distance between two points is half that. You never need to travel more than half way around the world. – Meir Maor Jul 25 '17 at 16:12

find nearest point (geometry point)

2 Answers2