Using GeoWebCache

Note

For an more in-depth discussion of using GeoWebCache, please see the GeoWebCache documentation.

Direct integration with GeoServer WMS

GeoWebCache can be transparently integrated with the GeoServer WMS, and so requires no special endpoint or custom URL. In this way one can have the simplicity of a standard WMS endpoint with the performance of a tiled client.

Although this direct integration is disabled by default, it can be enabled by going to the Caching defaults page in the Web administration interface.

When this feature is enabled, GeoServer WMS will cache and retrieve tiles from GeoWebCache (via a GetMap request) only if all of the following criteria are followed:

  • WMS Direct integration is enabled (you can set this on the Caching defaults page)

  • tiled=true is included in the request (unless the Explicitly require TILED Parameter is unchecked. you can set this on the Caching defaults page)

  • The request only references a single layer

  • Caching is enabled for that layer

  • The image requested is of the same height and width as the size saved in the layer configuration

  • The requested CRS matches one of the available tile layer gridsets

  • The image requested lines up with the existing grid bounds

  • A parameter is included for which there is a corresponding Parameter Filter

In addition, when direct integration is enabled, the WMS capabilities document (via a GetCapabilities request) will only return the WMS-C vendor-specific capabilities elements (such as a <TileSet> element for each cached layer/CRS/format combination) if tiled=true is appended to the GetCapabilities request.

Note

For more information on WMS-C, please see the WMS Tiling Client Recommendation from OSGeo.

Note

GeoWebCache integration is not compatible with the OpenLayers-based Layer Preview, as the preview does not usually align with the GeoWebCache layer gridset. This is because the OpenLayers application calculates the tileorigin based on the layer’s bounding box, which is different from the gridset. It is, possible to create an OpenLayers application that caches tiles; just make sure that the tileorigin aligns with the gridset.

Virtual services

When direct WMS integration is enabled, GeoWebCache will properly handle requests to Virtual Services (/geoserver/<workspace>/wms?tiled=true&...).

Virtual services capabilities documents will contain <TileSet> entries only for the layers that belong to that workspace (and global layer groups), and will be referenced by unqualified layer names (no namespace). For example, the layer topp:states will be referred to as <Layers>states</Layers> instead of <Layers>topp:states</Layers>, and GetMap requests to the virtual services endpoint using LAYERS=states will properly be handled.

Supported parameter filters

With direct WMS integration, the following parameter filters are supported for GetMap requests:

  • ANGLE

  • BGCOLOR

  • BUFFER

  • CQL_FILTER

  • ELEVATION

  • ENV

  • FEATUREID

  • FEATUREVERSION

  • FILTER

  • FORMAT_OPTIONS

  • MAXFEATURES

  • PALETTE

  • STARTINDEX

  • TIME

  • VIEWPARAMS

If a request is made using any of the above parameters, the request will be passed to GeoServer, unless a parameter filter has been set up, in which case GeoWebCache will process the request.

GeoWebCache endpoint URL

When not using direct integration, you can point your client directly to GeoWebCache.

Warning

GeoWebCache is not a true WMS, and so the following is an oversimplification. If you encounter errors, see the Troubleshooting page for help.

To direct your client to GeoWebCache (and thus receive cached tiles) you need to change the WMS URL.

If your application requests WMS tiles from GeoServer at this URL:

http://example.com/geoserver/wms

You can invoke the GeoWebCache WMS instead at this URL:

http://example.com/geoserver/gwc/service/wms

In other words, add /gwc/service/wms in between the path to your GeoServer instance and the WMS call.

This end-point works using either:

  • WMS-C: A tileset description is included in the WMS GetCapabilities document instructing clients how to retrieve content as a series of tiles (each retrieved by a GetMap request). This technique supports HTTP caching taking advantage of the browser cache and any caching proxies deployed. This technique requires a client to be created with tile server support.

  • full-wms mode: GeoWebCache behaves as normal WMS supported ad-hoc WMS GetMapRequests. Each WMS Request is handled by obtaining the tiles required and stitching the result into a single image. This technique relies only on internal tile cache, but supports ad-hoc GetMap requests and does not require a client be constructed with tile server support.

    To enable this mode add the following in geowebcache.xml configuration file:

    <fullWMS>true</fullWMS>

    The fullWMS setting only effects the /gwc/service/wms endpoint and is not used by direct WMS integration.

As soon as tiles are requested through the gwc/service/wms endpoint GeoWebCache automatically starts saving them. The initial requests for each tile will not be accelerated since GeoServer will need to generate the tile and store it from subsequent use. To automate this process of requesting tiles, you can seed the cache. See the section on Seeding and refreshing for more details.

Disk quota

GeoWebCache has a built-in disk quota feature to prevent disk space from growing unbounded. You can set the maximum size of the cache directory, poll interval, and what policy of tile removal to use when the quota is exceeded. Tiles can be removed based on usage (“Least Frequently Used” or LFU) or timestamp (“Least Recently Used” or LRU).

Disk quotas are turned off by default, but can be configured on the Disk Quotas page in the Web administration interface.

Integration with external mapping sites

The documentation on the GeoWebCache homepage contains examples for creating applications that integrate with Google Maps, Google Earth, Bing Maps, and more.

Support for custom projections

The version of GeoWebCache that comes embedded in GeoServer automatically configures every layer served in GeoServer with the two most common projections:

  • EPSG:4326 (latitude/longitude)

  • EPSG:900913 (Spherical Mercator, the projection used in Google Maps)

You can also set a custom CRS from any that GeoServer recognizes. See the Gridsets page for details.

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