WMS reference¶

Introduction¶

The OGC Web Map Service (WMS) specification defines an HTTP interface for requesting georeferenced map images from a server. GeoServer supports WMS 1.1.1, the most widely used version of WMS, as well as WMS 1.3.0.

The relevant OGC WMS specifications are:

• OGC Web Map Service Implementation Specification, Version 1.1.1

• OGC Web Map Service Implementation Specification, Version 1.3.0

GeoServer also supports some extensions to the WMS specification made by the Styled Layer Descriptor (SLD) standard to control the styling of the map output. These are defined in:

• OpenGIS Styled Layer Descriptor Profile of the Web Map Service Implementation Specification, Version 1.1.0

Benefits of WMS¶

WMS provides a standard interface for requesting a geospatial map image. The benefit of this is that WMS clients can request images from multiple WMS servers, and then combine them into a single view for the user. The standard guarantees that these images can all be overlaid on one another as they actually would be in reality. Numerous servers and clients support WMS.

Operations¶

WMS requests can perform the following operations:

Exceptions¶

Formats in which WMS can report exceptions. The supported values for exceptions are:

GetCapabilities¶

The GetCapabilities operation requests metadata about the operations, services, and data (“capabilities”) that are offered by a WMS server.

The parameters for the GetCapabilities operation are:

GeoServer provides the following vendor-specific parameters for the GetCapabilities operation. They are fully documented in the WMS vendor parameters section.

A example GetCapabilities request is:

http://localhost:8080/geoserver/wms?
service=wms&
version=1.1.1&
request=GetCapabilities

There are three parameters being passed to the WMS server, service=wms, version=1.1.1, and request=GetCapabilities. The service parameter tells the WMS server that a WMS request is forthcoming. The version parameter refers to which version of WMS is being requested. The request parameter specifies the GetCapabilities operation. The WMS standard requires that requests always includes these three parameters. GeoServer relaxes these requirements (by setting the default version if omitted), but for standard-compliance they should always be specified.

The response is a Capabilities XML document that is a detailed description of the WMS service. It contains three main sections:

GetMap¶

The GetMap operation requests that the server generate a map. The core parameters specify one or more layers and styles to appear on the map, a bounding box for the map extent, a target spatial reference system, and a width, height, and format for the output. The information needed to specify values for parameters such as layers, styles and srs can be obtained from the Capabilities document.

The response is a map image, or other map output artifact, depending on the format requested. GeoServer provides a wide variety of output formats, described in WMS output formats.

The standard parameters for the GetMap operation are:

GeoServer provides a number of useful vendor-specific parameters for the GetMap operation. These are documented in the WMS vendor parameters section.

Example WMS request for topp:states layer to be output as a PNG map image in SRS EPGS:4326 and using default styling is:

http://localhost:8080/geoserver/wms?
request=GetMap
&service=WMS
&version=1.1.1
&layers=topp%3Astates
&styles=population
&srs=EPSG%3A4326
&bbox=-145.15104058007,21.731919794922,-57.154894212888,58.961058642578&
&width=780
&height=330
&format=image%2Fpng

The standard specifies many of the parameters as being mandatory, GeoServer provides the WMS Reflector to allow many of them to be optionally specified.

Experimenting with this feature is a good way to get to know the GetMap parameters.

Example WMS request using a GetMap XML document is:

<?xml version="1.0" encoding="UTF-8"?>
<ogc:GetMap xmlns:ogc="http://www.opengis.net/ows"
            xmlns:gml="http://www.opengis.net/gml"
   version="1.1.1" service="WMS">
   <StyledLayerDescriptor version="1.0.0">
      <NamedLayer>
        <Name>topp:states</Name>
        <NamedStyle><Name>population</Name></NamedStyle>
      </NamedLayer>
   </StyledLayerDescriptor>
   <BoundingBox srsName="http://www.opengis.net/gml/srs/epsg.xml#4326">
      <gml:coord><gml:X>-130</gml:X><gml:Y>24</gml:Y></gml:coord>
      <gml:coord><gml:X>-55</gml:X><gml:Y>50</gml:Y></gml:coord>
   </BoundingBox>
   <Output>
      <Format>image/png</Format>
      <Size><Width>550</Width><Height>250</Height></Size>
   </Output>
</ogc:GetMap>

GetFeatureInfo¶

The GetFeatureInfo operation requests the spatial and attribute data for the features at a given location on a map. It is similar to the WFS GetFeature operation, but less flexible in both input and output. Since GeoServer provides a WFS service we recommend using it instead of GetFeatureInfo whenever possible.

The one advantage of GetFeatureInfo is that the request uses an (x,y) pixel value from a returned WMS image. This is easier to use for a naive client that is not able to perform true geographic referencing.

The standard parameters for the GetFeatureInfo operation are:

Note: If you are sending a GetFeatureInfo request against a layergroup, all the layers in that layergroup must be set as “Queryable” to get a result (See WMS Settings on Layers page)

GeoServer supports a number of output formats for the GetFeatureInfo response. Server-styled HTML is the most commonly-used format. For maximum control and customisation the client should use GML3 and style the raw data itself. The supported formats are:

GeoServer provides the following vendor-specific parameters for the GetFeatureInfo operation. They are fully documented in the WMS vendor parameters section.

An example request for feature information from the topp:states layer in HTML format is:

http://localhost:8080/geoserver/wms?
request=GetFeatureInfo
&service=WMS
&version=1.1.1
&layers=topp%3Astates
&styles=
&srs=EPSG%3A4326
&format=image%2Fpng
&bbox=-145.151041%2C21.73192%2C-57.154894%2C58.961059
&width=780
&height=330
&query_layers=topp%3Astates
&info_format=text%2Fhtml
&feature_count=50
&x=353
&y=145
&exceptions=application%2Fvnd.ogc.se_xml

An example request for feature information in GeoJSON format is:

http://localhost:8080/geoserver/wms?
&INFO_FORMAT=application/json
&REQUEST=GetFeatureInfo
&EXCEPTIONS=application/vnd.ogc.se_xml
&SERVICE=WMS
&VERSION=1.1.1
&WIDTH=970&HEIGHT=485&X=486&Y=165&BBOX=-180,-90,180,90
&LAYERS=COUNTRYPROFILES:grp_administrative_map
&QUERY_LAYERS=COUNTRYPROFILES:grp_administrative_map
&TYPENAME=COUNTRYPROFILES:grp_administrative_map

The result will be:

{
"type":"FeatureCollection",
"features":[
   {
      "type":"Feature",
      "id":"dt_gaul_geom.fid-138e3070879",
      "geometry":{
         "type":"MultiPolygon",
         "coordinates":[
            [
               [
                  [
                     XXXXXXXXXX,
                     XXXXXXXXXX
                  ],
                  ...
                  [
                     XXXXXXXXXX,
                     XXXXXXXXXX
                  ]
               ]
            ]
         ]
      },
      "geometry_name":"at_geom",
      "properties":{
         "bk_gaul":X,
         "at_admlevel":0,
         "at_iso3":"XXX",
         "ia_name":"XXXX",
         "at_gaul_l0":X,
         "bbox":[
            XXXX,
            XXXX,
            XXXX,
            XXXX
         ]
      }
   }
],
"crs":{
   "type":"EPSG",
   "properties":{
      "code":"4326"
   }
},
"bbox":[
   XXXX,
   XXXX,
   XXXX,
   XXXX
]
}

DescribeLayer¶

The DescribeLayer operation is used primarily by clients that understand SLD-based WMS. In order to make an SLD one needs to know the structure of the data. WMS and WFS both have operations to do this, so the DescribeLayer operation just routes the client to the appropriate service.

The standard parameters for the DescribeLayer operation are:

GeoServer supports a number of output formats for the DescribeLayer response. Server-styled HTML is the most commonly-used format. The supported formats are:

An example request in XML (default) format on a layer is: :

http://localhost:8080/geoserver/topp/wms?service=WMS &version=1.1.1 &request=DescribeLayer &layers=topp:coverage

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE WMS_DescribeLayerResponse SYSTEM "http://localhost:8080/geoserver/schemas/wms/1.1.1/WMS_DescribeLayerResponse.dtd">
<WMS_DescribeLayerResponse version="1.1.1">
   <LayerDescription name="topp:coverage" owsURL="http://localhost:8080/geoserver/topp/wcs?" owsType="WCS">
      <Query typeName="topp:coverage"/>
   </LayerDescription>
</WMS_DescribeLayerResponse>

An example request for feature description in JSON format on a layer group is:

http://localhost:8080/geoserver/wms?service=WMS
&version=1.1.1
&request=DescribeLayer
&layers=sf:roads,topp:tasmania_roads,nurc:mosaic
&outputFormat=application/json

The result will be:

{
  version: "1.1.1",
  layerDescriptions: [
    {
        layerName: "sf:roads",
        owsURL: "http://localhost:8080/geoserver/wfs/WfsDispatcher?",
        owsType: "WFS",
        typeName: "sf:roads"
    },
    {
        layerName: "topp:tasmania_roads",
        owsURL: "http://localhost:8080/geoserver/wfs/WfsDispatcher?",
        owsType: "WFS",
        typeName: "topp:tasmania_roads"
    },
    {
        layerName: "nurc:mosaic",
        owsURL: "http://localhost:8080/geoserver/wcs?",
        owsType: "WCS",
        typeName: "nurc:mosaic"
    }
  ]

GetLegendGraphic¶

The GetLegendGraphic operation provides a mechanism for generating legend graphics as images, beyond the LegendURL reference of WMS Capabilities. It generates a legend based on the style defined on the server, or alternatively based on a user-supplied SLD. For more information on this operation and the various options that GeoServer supports see GetLegendGraphic.