public GeoObject operate(GeoGrid geoGrid, double firstContourLevel) {
   float[] minMax = geoGrid.getMinMax();
   return operate(geoGrid, firstContourLevel, minMax[1]);
 }
 public GeoObject operate(GeoGrid geoGrid) {
   float[] minMax = geoGrid.getMinMax();
   final double firstContourLevel = Math.ceil(minMax[0] / interval) * interval;
   return operate(geoGrid, firstContourLevel);
 }