opencv - Draw convex hull on android -

i try draw convex hull on image.for this, find contours , select max area contour. drawcontours accepts matofpoint convexhull gives me matofint. read question , run codes. of them draw convex hull, cannot find convex points.

i use below code, has runtime error on last line m.fromarray(hullpoints.get(i));. hullpoints.get(i) has 1 point , code cannot create matofpoint object. how can convert matofpoint matofint ?

        // find convex hull         list<matofint> hull = new arraylist<matofint>();         for(int j=0; j < contours.size(); j++){             hull.add(new matofint());         }         for(int j=0; j < contours.size(); j++){             imgproc.convexhull(contours.get(j), hull.get(j));         }          // convert matofint matofpoint drawing convex hull         // loop on contours         list<point[]> hullpoints = new arraylist<point[]>();         for(int j=0; j < hull.size(); j++){             point[] points = new point[hull.get(j).rows()];              // loop on points need hulled in current contour             for(int k=0; k < hull.get(j).rows(); k++){                 int index2 = (int)hull.get(j).get(k, 0)[0];                 points[k] = new point(contours.get(j).get(index2, 0)[0], contours.get(j).get(index2, 0)[1]);             }             hullpoints.add(points);         }          // convert point arrays matofpoint         list<matofpoint> hullmop = new arraylist<matofpoint>();         for(int j=0; j < hullpoints.size(); j++){             matofpoint m = new matofpoint();             m.fromarray(hullpoints.get(i));             hullmop.add(m);         } 

fwiw, i've changed fastconvexhull here use com.google.android.gms.maps.model.latlong. minimally tested, no guarantees.

interface:

import com.google.android.gms.maps.model.latlng; import java.util.arraylist;  public interface convexhullalgorithm {     arraylist<latlng> execute(arraylist<latlng> points); } 

class:

public class fastconvexhull implements convexhullalgorithm {      @override     public arraylist<latlng> execute(arraylist<latlng> points) {         arraylist<latlng> xsorted = (arraylist<latlng>) points.clone();         collections.sort(xsorted, new xcompare());          int n = xsorted.size();          latlng[] lupper = new latlng[n];          lupper[0] = xsorted.get(0);         lupper[1] = xsorted.get(1);          int luppersize = 2;          (int = 2; < n; i++) {             lupper[luppersize] = xsorted.get(i);             luppersize++;              while (luppersize > 2 && !rightturn(lupper[luppersize - 3], lupper[luppersize - 2], lupper[luppersize - 1])) {                 // remove middle point of 3 last                 lupper[luppersize - 2] = lupper[luppersize - 1];                 luppersize--;             }         }          latlng[] llower = new latlng[n];          llower[0] = xsorted.get(n - 1);         llower[1] = xsorted.get(n - 2);          int llowersize = 2;          (int = n - 3; >= 0; i--) {             llower[llowersize] = xsorted.get(i);             llowersize++;              while (llowersize > 2 && !rightturn(llower[llowersize - 3], llower[llowersize - 2], llower[llowersize - 1])) {                 // remove middle point of 3 last                 llower[llowersize - 2] = llower[llowersize - 1];                 llowersize--;             }         }          arraylist<latlng> result = new arraylist<latlng>();          (int = 0; < luppersize; i++) {             result.add(lupper[i]);         }          (int = 1; < llowersize - 1; i++) {             result.add(llower[i]);         }          return result;     }      private boolean rightturn(latlng a, latlng b, latlng c) {         return (b.latitude - a.latitude) * (c.longitude - a.longitude) - (b.longitude - a.longitude) * (c.latitude - a.latitude) > 0;     }      private class xcompare implements comparator<latlng> {         @override         public int compare(latlng o1, latlng o2) {             return (new float(o1.latitude)).compareto(new float(o2.latitude));         }     } }