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I'm serving a layer via WMS that has multiple Polygons with transparency set to 30%. The polygons can overlap each other resulting in darker areas where the transparencies combine. Is it possible to prevent this?

UPDATE: Transparency is set via <CssParameter name="fill-opacity">0.5</CssParameter> of <Fill> element in SLD definition. The whole SLD looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor version="1.0.0" 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"
  xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
  <NamedLayer>
    <Name>plochaQ5ZU</Name>
    <UserStyle>
      <Name>Q5ZU</Name>
      <FeatureTypeStyle>

        <Rule>
          <Name>Q5ZU</Name>
          <Title>Q5ZU</Title>
          <PolygonSymbolizer>
            <Fill>
              <CssParameter name="fill">#0070D4</CssParameter>
              <CssParameter name="fill-opacity">0.5</CssParameter>
            </Fill>
          </PolygonSymbolizer>
        </Rule>
      </FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

I'm using OpenLayers to display the layer.

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How have you set the layer transparancy, including your SLD will help understand what you are trying to achieve and get you a better answer. What Client are you using to display the layers? P;ease update your question with this information. Cheers –  Mark C Nov 21 '13 at 7:19
    
Edited question. –  zimmi Nov 21 '13 at 9:42
    
Ok, you are styling Polygons on a Layer, not styling a Layer. Now, is there two layers being styled, or are you referring to the case where two Polygons on the same layer overlap each other? –  Mark C Nov 22 '13 at 0:31
    
Two polygons on the same layer. –  zimmi Nov 22 '13 at 10:50
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1 Answer

up vote 1 down vote

You have two polygons that overlap with transparency set. This results in the overlaps appearing darker.

As far as I Know, the SLD for Polygons does not allow for partial transparencies within an individual Polygon area, you would have to truncate your polygons where the overlap occurred and create a new polygon to replace the overlapped area then style the new polygon to the same transparency.

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