code: int closestPoint( Point2D_F64 target ) {
  		double bestDistance = Double.MAX_VALUE;
  		int bestIndex = -1;
  		for (int i = 0; i < contour.size(); i++) {
  			Point2D_I32 c = contour.get(i);
  
  			double d = UtilPoint2D_F64.distanceSq(target.x,target.y,c.x,c.y);
  			if( d < bestDistance ) {
  				bestDistance = d;
  				bestIndex = i;
  			}
  		}
  		return bestIndex;
  	}
docs: Returns the closest point on the contour to the provided point in space
  @return index of closest point