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 geosolutions: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 geosolutions:streams against the FeatureCollection collected from the Vector Layer geosolutions:restricted.

../_images/wps_5_1.png

Vector clip and ship

Vector clip and ship

  1. Once started the GeoServer, 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 geosolutions:states FeatureCollection

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

../_images/wps_5_7.png

Raster clip and ship

Raster clip and ship

  1. Once started the GeoServer, go to the Demo WPS Request Builder interface, and select gs:CropCoverage from the first combo-box. Select the Raster Layer geosolutions:usa 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 geosolutions: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 through 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.

Warning

At this time GeoServer is 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, 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

    Warning

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

Warning

If you see a coverage - GridCoverage2D input, set it to TEXT image/Tiff and leave the textbox blank.

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

    ../_images/wps_5_16.png