code: protected GridCoverage2D getGridCoverage( int readerNum, double north, double south, double east, double west )
              throws Exception {
          GeneralParameterValue[] readGeneralParameterValues = CoverageUtilities.createGridGeometryGeneralParameter(xRes, yRes,
                  north, south, east, west, crs);
  
          ImageMosaicReader reader = readers.get(readerNum);
          GridCoverage2D readGC = reader.read(readGeneralParameterValues);
          return readGC;
      }
docs: Get the {@link GridCoverage2D} in a certain region.
  
  <p>It might be usefull for faster access to the underlying data to
  extract the raster before creatin the iterator, instead of iterating
  directly.
  <p>This can be done on the returned gridcoverage through:
  <code>
  Raster readRaster = readGC.getRenderedImage().getData();
  RandomIter readIter = RandomIterFactory.create(readRaster, null);
  </code>
  
  @param readerNum the number of the reader to use.
  @param north
  @param south
  @param east
  @param west
  @return the gridcoverage inside the supplied bounds.
  @throws Exception