[GIS] Single Image WMS in GeoServer to clear duplicate labels

geoserverlabelingopenlayers-2wms

I have set up GeoServer with PostgreSQL/PostGIS as database.
Imported a country boundary shapefile into the database and published as WMS.
The data has got the Country name attribute in the "label" column.
I setup a map client using Openlayers, and it shows so many labels when zoomed in, one for each tile.

Can I publish the wms map as a Single Image, (without multiple image tiles) to avoid duplicate country name labels?

Or is there any other successful methods to do this in SLD?

I have read many answers and tried vendor options to correct this, nothing worked.
Some similar questions were seen as removed as duplicates, but sincerely, I got no solution for this duplicate label issue in GeoServer.

More Info:
I am using GeoServer 2.7.0
Using openlayers javascript from :

http://openlayers.org/api/OpenLayers.js

And the Openlayers code is: 

<script type="text/javascript">
    var map;
    function init() {
        map = new OpenLayers.Map({
            div: "map",
            projection: new OpenLayers.Projection("EPSG:900913"),
            controls: [],
            numZoomLevels: 8,
            maxZoomLevel: 16
        });
        var osm = new OpenLayers.Layer.OSM("Open Street");
        var gmap = new OpenLayers.Layer.Google("Google Streets");

        Layer1 = new OpenLayers.Layer.WMS("1648", "http://localhost:8080/geoserver/wms", 
        { layers: 'my_wor:Layer1', transparent: true },
        { isBaseLayer: false });

        Layer2 = new OpenLayers.Layer.WMS("2015", "http://localhost:8080/geoserver/wms", 
        { layers: 'my_wor:Layer2', transparent: true },
        { isBaseLayer: false });

        map.addLayers([gmap, osm, Layer1, Layer2]);

        map.addControl(new OpenLayers.Control.LayerSwitcher());
        map.addControl(new OpenLayers.Control.ScaleLine());
        map.addControl(new OpenLayers.Control.OverviewMap());
        map.addControl(new OpenLayers.Control.Navigation());
        map.addControl(new OpenLayers.Control.PanZoomBar());
</script>

See the SLD below, with the vendor options "group" is given true.

<?xml version="1.0" encoding="ISO-8859-1"?>
<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>Polygon with styled label</Name>
<UserStyle>
<Title>SLD Cook Book: Polygon with styled label</Title>
<FeatureTypeStyle>
<Rule>
<PolygonSymbolizer>
<Fill>
<CssParameter name="fill">#FF0000</CssParameter>
</Fill>
<Stroke>
<CssParameter name="stroke">#CCCCCC</CssParameter>
<CssParameter name="stroke-width">1</CssParameter>
</Stroke>
</PolygonSymbolizer>
<TextSymbolizer>
<Label>
<ogc:PropertyName>label</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>0.5</AnchorPointY>
</AnchorPoint>
</PointPlacement>
</LabelPlacement>
<Fill>
<CssParameter name="fill">#000000</CssParameter>
</Fill>
<VendorOption name="autoWrap">160</VendorOption>
<VendorOption name="repeat">0</VendorOption>
<VendorOption name="group">true</VendorOption>
<VendorOption name="labelAllGroup">false</VendorOption>
</TextSymbolizer>
</Rule>
</FeatureTypeStyle>
</UserStyle>
</NamedLayer>
</StyledLayerDescriptor>

Best Answer

I will try to be as clear as possible, but I am not sure I understood everything that your are asking. You might want to edit your post with additional information or a concrete example and the version of Geoserver you are using.

Problem 1: you have duplicate labels due to the tiling of your WMS request by OL

-> solution: in Open Layer, request a single WMS image (see example here http://openlayers.org/en/v3.1.1/examples/wms-image.html)

Problem 2: you have duplicate labels due to multi geometries

-> solution: use the vendor option group in Geoserver SLD

The group option allows displaying a single label for multiple features in a logical group.

(see here http://docs.geoserver.org/latest/en/user/styling/sld-reference/labeling.html)

These are not miracle solutions and you might still need to tweek your SLD to get exactly what you want.

EDIT – regarding Problem 2

A possible trick I used on a small dataset: manually delete the label value for the smaller entities of my multi-geometries. However, I would not consider this good practice.

Another trick would be to create a additional column in your database and to assign 1 (=need a label) and 0 (=does not need a label) and to use it in a conditional filter in SLD to tell Geoserver whether to draw a label or not

EDIT 2

(after the comment from @user30184 & @OpenMapperz)

This is the same example, but for OL3 here http://openlayers.org/en/master/examples/wms-image.html?q=wms

If you want to find the relevant syntax, look at the OL3 documentation. The relevant point here is to use the object ol.layer.Image with ol.layer.ImageWMS.

Related Question