Label styling applied in Geoserver are not being applied to WMS layer in Openlayers

Question

I am trying to label a layer of line vectors using SLD in Geoserver. It is simple enough, and it's pretty much copied from the SLD cookbook: http://docs.geoserver.org/latest/en/user/styling/sld-cookbook/lines.html

The thing that's getting me is that when I view the Openlayers preview in Geoserver, everything seems to render correctly. Each road is only labeled once and it's not extremely busy looking. However, when I import the layer via WMS to my Openlayers map, it doesn't seem to recognize this line:

<VendorOption name="repeat">400</VendorOption> 

Which is supposed to keep it from repeating within 400 pixels.

I've also tried:

<VendorOption name="group">yes</VendorOption> 

Which should only display a single label on a map per unique text.

Any idea what is going on here? I need the labels to look like the Geoserver preview.

Map displayed in openlayers after importing layer via WMS:

Map displayed in Geoserver Openlayers preview:

<?xml version="1.0" encoding="UTF-8"?> <StyledLayerDescriptor version="1.0.0" xsi:schemaLocation="http://www.opengis.net/sld 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>Roads</Name> <UserStyle> <FeatureTypeStyle> <Rule> <Title>Roads</Title> <LineSymbolizer> <Stroke> <CssParameter name="stroke"> <ogc:Literal>#000000</ogc:Literal> </CssParameter> <CssParameter name="stroke-width"> <ogc:Literal>1</ogc:Literal> </CssParameter> </Stroke> </LineSymbolizer> <TextSymbolizer> <Label> <ogc:PropertyName>name</ogc:PropertyName> </Label> <LabelPlacement> <LinePlacement> <PerpendicularOffset> 10 </PerpendicularOffset> </LinePlacement> </LabelPlacement> <Fill> <CssParameter name="fill">#000000</CssParameter> </Fill> <VendorOption name="repeat">400</VendorOption> </TextSymbolizer> </Rule> </FeatureTypeStyle> </UserStyle> </NamedLayer> </StyledLayerDescriptor>

Answer 1

This is probably an artifact due to tiling. The layer preview map defaults to a single tile, but I'm guessing your openlayers map uses tiling.

Geoserver insists on labeling every tile. GeoServer doesn't know that each request is for a tile in a larger map, so it treats a tile as a complete map and dutifully applies a label to it. So basically, if a road stretches across three tiles, it will be labelled three times.

Unfortunately, there's not much you can do about it. I was advised to enable meta-tiling. This does allow GeoServer to think of requests as tile components to some extent, and this can minimise the label repeating. However, I believe it's on by default in recent versions.

Answer 2

You can try this on Ol side

import TileLayer from "ol/layer/Image";
import ImageWMS from 'ol/source/ImageWMS';
import { geoserverURL } from '../config';

const BuildingWMS = new TileLayer({
    source: new ImageWMS({
        ratio:1,
        projection: 'EPSG:3857',
        url: `${geoserverURL}/wms?`,
        params: {
            'LAYERS': 'Baku:Buildings',
            'FORMAT': 'image/png',
            'VERSION': '1.1.1',
        },
        serverType: 'geoserver',
        crossOrigin: 'anonymous'
    }),
    visible: true,
    name: 'BuildingWMS'
});
export {
    BuildingWMS
};