code: public Double getValue(GriddedTile griddedTile, BufferedImage image, int x,
  			int y) {
  		short pixelValue = getPixelValue(image, x, y);
  		Double value = getValue(griddedTile, pixelValue);
  		return value;
  	}
docs: Get the coverage data value
  
  @param griddedTile
  gridded tile
  @param image
  tile image
  @param x
  x coordinate
  @param y
  y coordinate
  @return coverage data value