CODEWITHSUNDEEP
javagisgeotools
George
George

Reputation: 5691

find nearest point (geometry point)

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;
}

Upvotes: 4

Views: 902

Answers (2)

Meir Maor
Meir Maor

Reputation: 1210

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.

Upvotes: 0

bracco23
bracco23

Reputation: 2221

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.

Upvotes: 1

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