GeoServer Multi-band Image Using the Same Style

Introduction#

The requirement is to have a dataset of ocean features with 12 channels, corresponding to data for 12 months. After the layer is published, styles can be used to select the corresponding channel to display data for a specific month. A simple and straightforward approach is to copy 12 styles, but for easier future maintenance (most likely to be maintained by oneself), I wanted to find a way similar to "dynamic styles" that can fetch parameters from external sources, using the same style to select different channels through different parameters.

Here, I was slightly misled by my own assumptions: the version of GeoServer used in the production environment is relatively low, 2.11.x. When I looked at the documentation, I was looking at the latest version, and after testing it didn't work, I checked the 2.11 documentation. Although there are similar usages in the documentation, it is not applicable when selecting channels.

Therefore, this method is only suitable for newer versions.

Layer Publishing#

Layer publishing can theoretically handle multi-channel images.

Setting Styles#

The general form of channel selection for band merging is as follows¹.

<ChannelSelection>
  <RedChannel>
    <SourceChannelName>1</SourceChannelName>
  </RedChannel>
  <GreenChannel>
    <SourceChannelName>2</SourceChannelName>
  </GreenChannel>
  <BlueChannel>
    <SourceChannelName>3</SourceChannelName>
  </BlueChannel>
</ChannelSelection>

In the style, channels 1, 2, and 3 correspond to (R, G, B).

For selecting a single channel for display, use Function to obtain "environment variables" and replace default values.

<RasterSymbolizer>
  <Opacity>1.0</Opacity>
  <ChannelSelection>
    <GrayChannel>
      <SourceChannelName>
            <Function name="env">
             <ogc:Literal>m</ogc:Literal>
             <ogc:Literal>1</ogc:Literal>
          </ogc:Function>
      </SourceChannelName>
    </GrayChannel>
  </ChannelSelection>
</RasterSymbolizer>

Here, the channel name wraps a Function object, which provides 1 as the default value when the value of m in env is empty. If m is not empty, the value of m is used as the channel name.

In the wms request, adding &env=m:2 will select the channel numbered 2 for display.

http://localhost:8083/geoserver/wms?service=WMS&version=1.1.0&request=GetMap&layers=geosolutions:usa&styles=&bbox=-130.85168,20.7052,-62.0054,54.1141&width=768&height=372&srs=EPSG:4326&format=application/openlayers&env=m:2

Here is a complete style:

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor 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" version="1.0.0">
  <NamedLayer>
    <Name>saltsld</Name>
    <UserStyle>
      <Title>A raster style</Title>
      <FeatureTypeStyle>
        <Rule>
          <RasterSymbolizer>
            <Opacity>1.0</Opacity>
            <ChannelSelection>
                <GrayChannel>
                        <SourceChannelName><ogc:Function name="env">
                    <ogc:Literal>m</ogc:Literal>
                    <ogc:Literal>1</ogc:Literal>
            </ogc:Function></SourceChannelName>
                </GrayChannel>
        </ChannelSelection>
            <ColorMap>
           <ColorMapEntry color="#0000ff" quantity="28.0"/>
           <ColorMapEntry color="#009933" quantity="30.0"/>
           <ColorMapEntry color="#ff9900" quantity="32.0" />
           <ColorMapEntry color="#ff0000" quantity="34.0"/>
 </ColorMap>
          </RasterSymbolizer>
        </Rule>
      </FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

September

March

Conclusion#

Ultimately, due to the difficulty in updating the production environment version, I ended up copying 12*2 styles myself.

GeoServer : RasterSymbolizer ↩