Geotools Sld TextSymbolizer drawes text to wrong places

Question

im using geotools GTRenderer as a Tileserver and have a SLD File for styling (taken from here https://docs.geoserver.org/stable/en/user/styling/sld/cookbook/points.html#point-with-styled-label):

<StyledLayerDescriptor version="1.0.0"
                   xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd"
                   xmlns="http://www.opengis.net/sld"
                   xmlns:ogc="http://www.opengis.net/ogc"
                   xmlns:xlink="http://www.w3.org/1999/xlink"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<NamedLayer>
    <Name>WorldCities</Name>
    <UserStyle>
        <Name>Default Styler</Name>
        <FeatureTypeStyle>
            <Name>name</Name>
            <Rule>
                <PointSymbolizer>
                    <Graphic>
                        <Mark>
                            <WellKnownName>circle</WellKnownName>
                            <Fill>
                                <CssParameter name="fill">#FF0000</CssParameter>
                            </Fill>
                        </Mark>
                        <Size>6</Size>
                    </Graphic>
                </PointSymbolizer>
                <TextSymbolizer>
                    <Label>
                        <ogc:PropertyName>nameascii</ogc:PropertyName>
                    </Label>
                    <Font>
                        <CssParameter name="font-family">Arial</CssParameter>
                        <CssParameter name="font-size">12</CssParameter>
                        <CssParameter name="font-style">normal</CssParameter>
                        <CssParameter name="font-weight">bold</CssParameter>
                    </Font>
                    <LabelPlacement>
                        <PointPlacement>
                            <AnchorPoint>
                                <AnchorPointX>0.5</AnchorPointX>
                                <AnchorPointY>0.0</AnchorPointY>
                            </AnchorPoint>
                            <Displacement>
                                <DisplacementX>0</DisplacementX>
                                <DisplacementY>5</DisplacementY>
                            </Displacement>
                        </PointPlacement>
                    </LabelPlacement>
                    <Fill>
                        <CssParameter name="fill">#000000</CssParameter>
                    </Fill>
                </TextSymbolizer>

            </Rule>
        </FeatureTypeStyle>
    </UserStyle>
</NamedLayer>

The PointSymbolizer works and I get one one point at the desired location, but the text symbolizer produces hunderds of labels:

In this sample output, the place "Southend-on-Sea" is the only one i expect to be rendered.

Any idea what might be different between the point and the textsymbolizer?

Thanks for any help

Edit the code i use:

private static Style loadStyleFromXml(String path) throws Exception {
    StyleFactory factory = CommonFactoryFinder.getStyleFactory();
    URL resource = new File(path).toURI().toURL();
    SLDParser stylereader = new SLDParser( factory, resource);
    Style styles[] = stylereader.readXML();
    return styles[0];
}
private static FeatureSource<SimpleFeatureType, SimpleFeature> readShapefile(String path) throws IOException {
    File file = new File(path);
    Map<String, Object> filemap = new HashMap<>();
    filemap.put("url", file.toURI().toURL());

    DataStore dataStore = DataStoreFinder.getDataStore(filemap);
    String typeName = dataStore.getTypeNames()[0];
    FeatureSource<SimpleFeatureType, SimpleFeature> source = dataStore.getFeatureSource(typeName);
    SimpleFeatureType schema = source.getSchema();
    return source;
}

Tile render method:

public synchronized byte[] renderRasterTile(int x, int y, int z){
    ReferencedEnvelope tileBounds = WebMercatorTileFactory.getExtentFromTileName(new OSMTileIdentifier(x, y, new WebMercatorZoomLevel(z), "custom"));
    try {
        tileBounds = tileBounds.transform(CRS.decode("EPSG:3857"),true);
    } catch (Exception e) {
        logger.error("Unable to transfrom coords",e);
        throw new RuntimeException(e);
    }
    BufferedImage image = new BufferedImage(tilePixelSize.width, tilePixelSize.height, BufferedImage.TYPE_INT_RGB);

    Graphics2D gr = image.createGraphics();
    gr.setPaint(new Color(0,0,0, (float) 0.1));
    gr.fill(tilePixelSize);

    try {
        renderer.paint(gr, tilePixelSize, tileBounds);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write( image, "png", baos );
        baos.flush();
        byte[] imageInByte = baos.toByteArray();
        baos.close();
        return imageInByte;
    } catch (IOException e) {
        logger.error("Unable to render tile",e);
        throw new RuntimeException(e);
    }
}
public MapContent setupMap(){
MapContent map = new MapContent();
map.setTitle("WorldMap");

FeatureSource<SimpleFeatureType, SimpleFeature> featureSource = readShapefile("cities.shp");

Style style = loadStyleFromXml("cities.sld");
Layer layer = new FeatureLayer(featureSource, style,"cities");
map.addLayer(layer);
return map;
}

The Shapefile I used can be downloaded here:

https://www.naturalearthdata.com/downloads/10m-cultural-vectors/10m-populated-places/

Answer 1

It's hard to be sure as there are some elements missing from your code but I get reasonable looking results from this code:

   try {
        StreamingRenderer renderer = new StreamingRenderer();
        MapViewport viewport = new MapViewport();
        viewport.setBounds(tileBounds);
        map.setViewport(viewport);
        renderer.setMapContent(map);
        renderer.paint(gr, tilePixelSize, tileBounds);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write( image, "png", baos );
        baos.flush();
        byte[] imageInByte = baos.toByteArray();
        baos.close();
        return imageInByte;
    } catch (IOException e) {
        System.err.println("Unable to render tile "+e);
        throw new RuntimeException(e);
    }

The key part is where I set the viewport bounds for the renderer:

        MapViewport viewport = new MapViewport();
        viewport.setBounds(tileBounds);
        map.setViewport(viewport);
        renderer.setMapContent(map);

otherwise the renderer is still using WGS84 (the CRS of the layer, assuming nothing else is set) while your bounds are in EPSG:3857 so the whole world gets drawn.

For values of X=16, Y=10 and Z=5 I get this tile:

Update

On further investigation, as you comment there is a problem if you draw two tiles in a row from a single renderer which I'm pretty sure you should be able to do. So it looks like a bug in the renderer not clearing the label cache when it starts to draw a new area. Feel free to post a bug on the JIRA.

For the time being you can work round it by providing your own LabelCache and clearing it each time you call paint.

GTRenderer renderer = new StreamingRenderer();
LabelCache cache = new LabelCacheImpl();
private void setup(){
    Map<Object, Object> hints = new HashMap<>();
    hints.put(StreamingRenderer.LABEL_CACHE_KEY, cache);
    renderer.setRendererHints(hints);
}

and then add

cache.clear(); 

in the renderRasterTile method, seems to work for me.