Process Chaining

GeoServer WPS implements also the Process Chaining. As the wording suggests, this is a method of “nesting” different processes inputs/outputs in order to get a chain of operations composing a unique more complex Process.

WPS Process Chaining is a way to:

  • Feeding the output of a process into another process
  • Allowing for tree-like composition

Lets see a couple of Process Chaining examples:

  1. Extract the rivers into the “restricted areas” polygons
  2. Extract the shape of the USA out of a raster, providing the topp:states FeatureCollection

Chain 1: Extract the rivers into the “restricted areas” polygons

During this exercise we will perform a gs:Clip of the Vector Layer sf:streams against the FeatureCollection collected from the Vector Layer sf:restricted.

../_images/wps_5_1.png

Vector clip and ship

Vector clip and ship

  1. Once started the GeoServer Trunk on port 8085 (WPS - Startup the service section), go to the Demo WPS Request Builder interface, and select gs:Clip from the first combo-box. Select the Vector Layer sf:streams as input.

    ../_images/wps_5_2.png

  2. Now, for the clip input select SUBPROCESS and then click on Define/edit. Another WPS Builder dialog window should appear.

    ../_images/wps_5_3.png

  3. On the new WPS Browser window select the process gs:CollectGeometries using the Vector Layer sf:restricted, then Apply

    ../_images/wps_5_4.png

  4. Finally select application/zip as output format and then Execute Process

    ../_images/wps_5_5.png

  5. After few instants you will be able to download a zip file containing a shapefile. Open the latter using uDig or QGis in order to inspect the outcomes

    ../_images/wps_5_6.png

Chain 2: Extract the shape of the USA out of a raster, providing the topp:states FeatureCollection

During this exercise we will perform a gs:CropCoverage of the Raster Layer nurc:Img_Sample against the FeatureCollection collected from the Vector Layer topp:states.

../_images/wps_5_7.png

Raster clip and ship

Raster clip and ship

  1. Once started the GeoServer Trunk on port 8085 (WPS - Startup the service section), go to the Demo WPS Request Builder interface, and select gs:CropCoverage from the first combo-box. Select the Raster Layer nurc:Img_Sample as input.

    ../_images/wps_5_8.png

  2. Now, for the cropGeometry input select SUBPROCESS and then click on Define/edit. Another WPS Builder dialog window should appear. On the new WPS Browser window select the process gs:CollectGeometries using the Vector Layer topp:states, then Apply

    ../_images/wps_5_9.png

  3. Leave image/tiff as output format for the Process and proceed with the Execute Process

    ../_images/wps_5_10.png

GeoServer “direct data integration” and “store Back”” capabilities throught gs:Import

Direct data integration

The WPS normally streams input data from remote WFS/WCS, parsing GML/GeoJSON or GeoTiff/ArcGrid. On the GeoServer implementation when the source is local we can dodge it though, read directly from the source (shapefile, DBMS, geotiff).

The following two special functions do the trick

  • http://geoserver/wfs; url for local WFS access
  • http://geoserver/wcs; url for local WCS access
../_images/wps_5_11.png

Store Back`` with ``gs:Import``

The gs:Import WPS Process along with Process Chaining can be successfully used to store back the outcomes as new GeoServer resources/layers.

gs:Import saves the vector results into a store of choice, and publish as a layer. The new resource can be used right away from WMS/WFS/WCS/WPS.

Attention

At this time GeoServer still missing the equivalent for rasters.

As an example, we will now store back into GeoServer the layer of reduced sf:roads created in the section Vector Processes

  1. Once started the GeoServer Trunk on port 8085 (WPS - Startup the service section), go to the Demo WPS Request Builder interface, and select gs:Import from the first combo-box

    ../_images/wps_5_12.png

  2. As input for features select SUBPROCESS, click on Details/edit and configure a gs:Clip Process on the Vector Layer sf:roads following the steps at Vector Processes section

    ../_images/wps_5_13.png

    Attention

    Don’t forget to specify the clipping geometry as WKT:

    POLYGON((589800.30577 4927510.97152, 589800.30577 4926799.69435, 590874.57957 4926799.69435, 590874.57957 4927510.97152, 589800.30577 4927510.97152))

  3. Click on Apply in order to let the Demo WPS Builder insert the Execute Process XML of the gs:Clip chained sub-process into the text-area

    ../_images/wps_5_14.png

  4. Fill in the other attributes

    • workspace; sf
      • name; roads_clipped
      • srs; EPSG:26713 (the sf:roads native one)
      • style; simple_roads (the default style to be assigned to the layer)
    ../_images/wps_5_15.png

  5. Click on the Execute Process and when finished check throught the GeoServer Layer Preview that the new layer has been created and is clipped

    ../_images/wps_5_16.png