GeoTools PolygonExtractionProcess demo

geotools_PolygonExtractionProcess_demo.java

    public static void main(String[] args) throws Exception
    {
        final int WIDTH = 5;
        final int HEIGHT = 5;

        GridCoverageBuilder builder = new GridCoverageBuilder();

        builder.setEnvelope(0, 0, WIDTH, HEIGHT); // x_min, y_min, x_max, y_max
        /*
            According to the documentation, the min and max allowed values for the coordinates are to be specified here,
            i.e. it should say WIDTH - 1 and HEIGHT - 1. However, this leads to incorrect results, while the above code does not.
            So the documentation seems to be wrong.
         */

        builder.setImageSize(WIDTH, HEIGHT);
        // Will use sample value in the range x inclusive to y exclusive.
        builder.setSampleRange(0, 42);
        GridCoverageBuilder.Variable precipitation = builder.newVariable("precipitation", Unit.ONE);

        builder.getBufferedImage().getRaster().setSample(2, (HEIGHT - 1) - 2, 0, -99);

        GridCoverage2D coverage = builder.getGridCoverage2D();

        System.out.println(coverage);

        PolygonExtractionProcess extractor = new PolygonExtractionProcess();

        LinkedList<Range> classificationRanges = new LinkedList<Range>();
        classificationRanges.add(new Range(-0.5, true, 0.5, true));
        classificationRanges.add(new Range(0.5, true, 1.5, true));
        classificationRanges.add(new Range(1.5, true, 2.5, true));
        SimpleFeatureCollection result = extractor.execute(coverage, 0, true, null, null, classificationRanges, null);
        // As far as I can tell from the geotools source code, the progressListener is not used at all. So we can as well just pass null.

        SimpleFeatureIterator iterator = result.features();
        try{
            while(iterator.hasNext()) {
                SimpleFeature feature = iterator.next();
                System.out.println(feature);
            }
        } finally {
            iterator.close();
        }
        System.out.println(result);
    }

A quick-and-dirty demo for the PolygonExtractionProcess class from the GeoTools project.
The code creates a 5x5 raster, sets the cell at (2, 2) to value 1 and then calls the PolygonExtractionProcess.

Here is the output of the code:

GridCoverage2D["null", GeneralEnvelope[(0.0, 0.0), (5.0, 5.0)], DefaultEngineeringCRS["Cartesian 2D"]]
│   RenderedSampleDimension("precipitation":[0.0 ... 42.0])
│     ‣ Category("precipitation":[0...41])
└ Image=WritableRenderedImageAdapter[]

Mär 29, 2018 5:16:42 PM org.geotools.image.ImageWorker <clinit>
INFORMATION: Warp/affine reduction enabled: true
SimpleFeatureImpl:reclassified=[SimpleFeatureImpl.Attribute: the_geom<the_geom id=0>=POLYGON ((0 5, 0 0, 5 0, 5 5, 0 5), (2 3, 3 3, 3 2, 2 2, 2 3)), SimpleFeatureImpl.Attribute: value<value id=0>=1.0]
SimpleFeatureImpl:reclassified=[SimpleFeatureImpl.Attribute: the_geom<the_geom id=1>=POLYGON ((3 2, 3 3, 2 3, 2 2, 3 2)), SimpleFeatureImpl.Attribute: value<value id=1>=157.0]
org.geotools.data.collection.ListFeatureCollection@42b3b079

Version 19.0 of GeoTools was used for this demo.