WKT not using "metre" as measure unit in SLD

Question

After solvig this question, seems WKT is not respecting my intent to use "metre" as measure of distance.

I have this SLD:

      <FeatureTypeStyle>
        <Rule>
          <PointSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
            <Graphic>
              <Mark>
                <WellKnownName>wkt://POLYGON ((0 0, ${width} 0, ${width} ${length}, 0 ${length}, 0 0))</WellKnownName>
                <Fill>
                  <CssParameter name="fill">#009900</CssParameter>
                  <CssParameter name="fill-opacity">0.4</CssParameter>
                </Fill>
              </Mark>
              <Rotation><PropertyName>bearing</PropertyName></Rotation>
            </Graphic>
          </PointSymbolizer>
        </Rule>
        <Rule>
          <PointSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
            <Graphic>
              <Mark>
                <WellKnownName>circle</WellKnownName>
                <Fill>
                  <CssParameter name="fill">#f00505</CssParameter>
                </Fill>
              </Mark>
              <Size>10</Size>
            </Graphic>
          </PointSymbolizer>
        </Rule>     
      </FeatureTypeStyle>

Consider width=30 and length=100.

I can see the red point (seems to) respect a 10 metres radius, but the green rectangles do not.

How can I draw a Polygon in wkt using ground units? May I calculate all coordinates before pass it to the SLD? if so, how can I pass the entire wkt as a String?

Answer 1

I've found a little tricky solution: Need to use my reference system in the WKT coordinates.

First I need a function to calculate a new point using a point, an azimuth and distance as input:

public static Point projectPoint( double lon, double lat, double distance, double azimuth ) {
    System.out.println("> From: " + lon + "," + lat + " Az: " + azimuth + "  Dist: " + distance );
        
    DefaultGeographicCRS crs = DefaultGeographicCRS.WGS84;
        
    GeodeticCalculator calc = new GeodeticCalculator(crs);
    GeometryFactory geomFactory = new GeometryFactory();
        
    Point point = geomFactory.createPoint( new Coordinate(lon, lat) );
        
    calc.setStartingGeographicPoint(point.getX(), point.getY());
    calc.setDirection(azimuth, distance);
    Point2D p = calc.getDestinationGeographicPoint();
        
    Point result = geomFactory.createPoint( new Coordinate(p.getX(), p.getY() ) );

    System.out.println("   > To: " + result.getX() + "," + result.getY() );
        
    return result;
}

Now I need another function to draw the polygon I need, projecting points one from another starting at the reference coordinates ( the point geometry that will use this SLD ). This will take the reference point coordinates, width, length and bearing of the "ship" and draw a rectangle projecting its corner points.

private static Polygon getHull( double lon, double lat, double width, double length, double bearing ) {
    GeometryFactory geomFactory = new GeometryFactory();
    Point p0 = geomFactory.createPoint( new Coordinate(lon, lat) );
    Point p1 = PointProjector.projectPoint( lon, lat, width,  bearing + 90);
    Point p2 = PointProjector.projectPoint(p1.getX(), p1.getY(), length, bearing + 0 );
    Point p3 = PointProjector.projectPoint(p2.getX(), p2.getY(), width,  bearing + 270 );
    Point p4 = p0;
    Coordinate[] coords = new Coordinate[] { p0.getCoordinate(), p1.getCoordinate(),p2.getCoordinate(),p3.getCoordinate(),p4.getCoordinate() };
    LinearRing ring = geomFactory.createLinearRing( coords );
    LinearRing holes[] = null; 
    Polygon polygon = geomFactory.createPolygon(ring, holes );      
    return polygon;
}

Now I prefer to have another function to draw a MultiPolygon if a complex draw becomes necessary. This will draw the "ship" using separate parts (only a primitive hull for now).

public static String createShip( double lon, double lat, double width, double length, double bearing ) {
    GeometryFactory geomFactory = new GeometryFactory();
        
    Polygon hull = getHull( lon, lat, width, length, bearing );

    Polygon[] polygons = new Polygon[] { hull }; 
    MultiPolygon mp = geomFactory.createMultiPolygon( polygons );

    return mp.toText();
}

Now I have a WKT MultiPolygon representing my "ship" going to 45 deg:

System.out.println( ShipCreator.createShip(-43, -23, 1000, 5000, 45) );

The output:

select 
ST_GeomFromText(
'MULTIPOLYGON (((-43 -23, -42.993102589219724 -23.006384903984472, -42.95862364344146 -22.974455829056822, -42.965519108985276 -22.96807059921952, -43 -23)))'
, 4326);

... and the result:

The SLD must have a Property as the WKT content to allow pass it from the code (here called "wktgeom"):

<PointSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
  <Graphic>
    <Mark>
      <WellKnownName><PropertyName>wktgeom</PropertyName></WellKnownName>
      <Fill>
        <CssParameter name="fill">#009900</CssParameter>
        <CssParameter name="fill-opacity">0.4</CssParameter>
      </Fill>
    </Mark>
    <Rotation><PropertyName>bearing</PropertyName></Rotation>
  </Graphic>
</PointSymbolizer>

And the code:

Point point = this.vesselGeometryFactory.createPoint(new Coordinate(x, y));
this.vesselFeatureBuilder.set("coordinates", point);
this.vesselFeatureBuilder.set("lon", x);
this.vesselFeatureBuilder.set("lat", y);
        
this.vesselFeatureBuilder.set("length", 100);
this.vesselFeatureBuilder.set("width", 30);
        
this.vesselFeatureBuilder.set("bearing", bearing );
this.vesselFeatureBuilder.set("mmsi", mmsi);
        
        
String wktContent = ShipCreator.createShip( x, y, 50, 100, 45) ;
        
this.vesselFeatureBuilder.set("wktgeom", "wkt://" + wktContent);

SimpleFeature aVessel = this.vesselFeatureBuilder.buildFeature( String.valueOf( mmsi ) );

Obviously you need to assign the style to the layer:

Style style = getStyle( "vesselStyle.sld" );
this.vesselLayer = new FeatureLayer( this.vesselCollection, style );

I don't know if I must "turn" the polygon right in the getHull() function or draw it always pointing to north and use the tag <Rotation> to do the job ...

I hope I didn't do anything too scary !! Please be gentle in comments because it cost me a lot of effort.

EDIT

An alternative to this method is to pass the MultiPolygon geometry to the feature. Change the Feature geometry:

Polygon[] theShipGeom = ShipCreator.createShip( x, y, 50, 100, bearing) ;
MultiPolygon ship = this.vesselGeometryFactory.createMultiPolygon( theShipGeom );

And pass it :

this.vesselFeatureBuilder.set("coordinate", ship);

Or course you'll need to change the schema:

builder.add("coordinate", MultiPolygon.class);

This way you won't need to care about WKT in SLD.