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I have a Geotiff file which is published as a raster layer in Geoserver. I need to be able to calculate the coordinates of the max n values that are inside a given polygon.

I have found a WPS called gs:RasterZonalStatistics which returns the max value in a raster layer. But I need to modify its code to return the coordinates of the max value. And further more to return the coordinates of the max n values.

I have searched the geotools code, and found the two classes: org.geotools.process.raster.RasterZonalStatistics and org.geotools.process.raster.RasterZonalStatistics2. I've tried to understand their code and to find the place where I should change but with no success.

Could you please guide me to the place where the real logic of calculating the max value exists?

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As far as I can tell the logic for those classes is down it org.jaitools.media.jai.zonalstats.ZonalStats but it is fairly opaque.

For a simpler way to do it have a look at this code:

  private double findMax2(int band) throws TransformException {
    double max = Double.NEGATIVE_INFINITY;
    GridSampleDimension sampleDimension = cov.getSampleDimension(band);
    double[] nodataarr = sampleDimension.getNoDataValues();
    double[] nodata = nodataarr != null ? nodataarr : new double[] { Double.NaN };
    double[] dest = new double[cov.getNumSampleDimensions()];
    GridCoordinates2D mCoord = null;
    GridEnvelope2D gr = cov.getGridGeometry().getGridRange2D();
    for (int i = gr.getLow(0); i < gr.getHigh(0); i++) {
      for (int j = gr.getLow(1); j < gr.getHigh(1); j++) {
        GridCoordinates2D coord = new GridCoordinates2D(i, j);
        cov.evaluate(coord, dest);
        // System.out.println("" + i + "," + j + "\t " + dest[band] + " (" + max
        // + ")");
        if (dest[band] != nodata[0] && dest[band] > max) {
          max = dest[band];
          mCoord = coord;
        }
      }
    }

    System.out.println("" + max + " at " + mCoord + " " + cov.getGridGeometry().gridToWorld(mCoord));
    return max;
  }

Essentially, you need to loop through the coverage data and compare it to your current max and if it is bigger (and not NODATA) update where your highest point is.

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