[geomesa-users] KNN-Queries

[Marcel <m.jacob@xxxxxxxxxxx>]

Hi there,

I´ve got another question corresponding to query-writing. I have found no java documentation for Geomesa so far, thats why I have some problems writing queries. Please have a look at the following peace of code.
The code seems to work, but it doesn´t return anything. My aim is to return the closest event to beijing considering the attribute "geom". I found a KNNQuery class, but it´s not working for me, because there are some "magic" parameters I don´t understand (see comments in my code).

Thanks again.

Marcel.

public static void queryGdelt(String[] args) throws Exception {



        SimpleFeatureSource fs = GDELTGeomesaQueryClusterPreparation.getSimpleFeatureSource(args);

 

        GeometryFactory geomFactory = new GeometryFactory();

        // coordinates for beijing

        double[] coordinates = { 116.3974589, 39.9388838 };

        Coordinate coord = new Coordinate(coordinates[0], coordinates[1]);

        Point point = geomFactory.createPoint(coord);

 

        int unknownParameter1 = 1;

        // second parameter vague

        // attribute parameter "geom" missing? 

        NearestNeighbors neighborsPrepare = NearestNeighbors.apply(point, unknownParameter1);

 

        DateFormat df = new SimpleDateFormat("yyyy-MM-dd");

        Date start = df.parse("1979-01-01");

        FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();

        Filter timeFilter = ff.after(ff.property("SQLDATE"), ff.literal(start));

 

        // second and third parameter vague

        double unknownParameter2 = 1;

        double unknownParameter3 = 1;

        GeoHashSpiral spiral = GeoHashSpiral.apply(point, unknownParameter2, unknownParameter3);

        // i dont need an extra filter...knn is my spatialfilter.

        // took complete timeline, because the constructor for query needs a filter.

        NearestNeighbors neighbors = KNNQuery.runKNNQuery(fs,

                new Query("gdelt", timeFilter, new String[] { "SQLDATE", "geom" }), spiral, neighborsPrepare);

 

        // size is always 0


        Log.info(neighbors.size());

 

        // print the results

        Iterator<SimpleFeatureWithDistance> sfListWithDist = neighbors.getK().iterator();

        while (sfListWithDist.hasNext()) {

            SimpleFeatureWithDistance sfWithdist = sfListWithDist.next();

            double minimumDistance = sfWithdist.dist();

            int numberOfAttributes = sfWithdist.sf().getAttributeCount();

            String eventOutput = "";

            for (int currentAttributeNumber = 0; currentAttributeNumber < numberOfAttributes; currentAttributeNumber++) {

                Object o = sfWithdist.sf().getAttributes().get(currentAttributeNumber);

                if (o != null) {

                    eventOutput += o.toString() + " ";

                } else {

                    eventOutput += "NULL ";

                }

            }

            Log.info(minimumDistance + " " + eventOutput.trim());

        }

    }