Raster and Conversion Processes

Through the Raster Processes the WPS is able to execute operations and computations against gridded data sets.

Likely for the Vectorial Processes, those can be seen as an improvement/extension of the WCS, aka “All you wanted WCS to do for you but it never wanted to ...”

Examples of what we can do with the Raster Processes are:

• Add/Multiply; add and multiply two rasters (waiting for full algebra to be implemented)
• Crop; crop a coverage based on the specified cutting geometry
• RangeLookup; classify raster image based on a set of ranges ([min,max] -> value)
• ScaleCoverage; rescale and translate a given raster
• StyleCoverage; apply a SLD style to a raster, getting back a styled (but still georeferenced) one
• Georectify; turn a non geo-referenced coverage into one based on ground control points

Raster Processes

We are going now to execute a simple exercise, trying to crop-out an internal raster layer and get back the result.

We will execute a gs:CropCoverage process over a raster layer, providing a polygonal shape.

gs:CropCoverage example

gs:CropCoverage

The gs:CropCoverage process allows to clip a raster into another one provided a geometry shape. The process works on external sources too, not only GeoServer internal layers, differently from the WCS.

Starting from the full geosolutions:usa raster, representing the USA

we will issue the WPS gs:CropCoverage process to get back a clipped image to a smaller polygonal area

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

   

   Demo WPS Request Builder interface for gs:CropCoverage process

2. Select the RASTER_LAYER geosolutions:usa and for the first input, the geometry, select the type application/WKT and insert the following POLYGON into the text-area

   POLYGON((-99.65571 48.60102,
       -80.83055 37.17146,
       -98.44552 30.31373,
       -113.50564 41.07096,
       -99.65571 48.60102))
   

   Note

   The coordinates of the POLYGON are expressed in the native CRS of the coverage, in this case EPSG:4326.

   

   Demo WPS Request Builder interface for gs:CropCoverage process - input parameters

3. Click on the Execute Process button in order to get back the clipped Coverage in image/tiff format

   

Conversion Processes

A Conversion Process allows us to extract Vectorial Features out from Rasters.

Examples of Conversion Process are:

• Contour; extracts isolines given a set of levels or a interval
• RasterAsPointCollection; extracts one point for each cell with band contents as attributes
• PolygonExtraction; extracts uniform polygons from raster, eventually given a set of value ranges
• RasterZonalStatistics; given a raster and a polygonal compute min/max/sum/avg/stddev of the cells falling in each polygon return an augmented polygonal
• VectorToRaster; rasterizes vectors keeping a chosen attribute (a CQL expression eventually) as the band value

We will now execute a gs:Contour process over a raster DEM layer in order to get back the isolines on a set of levels.

gs:Contour example

gs:Contour

1. Once started the GeoServer, go to the Demo WPS Request Builder interface, and select gs:Contour from the first combo-box

   

   Demo WPS Request Builder interface for gs:Contour process

2. Select the RASTER_LAYER geosolutions:dem for the first combo-box

   Warning

   We need to provide more than one input level, however we cannot provide multi-valued inputs using the current Demo WPS Request Builder. We must therefore let the Demo Builder provide a template Execute Process XML template, which we will manually modify later.

3. Insert on the levels text-box the value 1200 and select type=text/xml; subtype=wfs-collection/1.0 as output format for the result

   

4. Click on the Generate XML from process inputs/outputs button, in order to get back the following Execute Process XML

   <wps:Execute version="1.0.0" service="WPS" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wps/1.0.0" xmlns:wfs="http://www.opengis.net/wfs" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:wcs="http://www.opengis.net/wcs/1.1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsAll.xsd">
     <ows:Identifier>gs:Contour</ows:Identifier>
     <wps:DataInputs>
           <wps:Input>
             <ows:Identifier>data</ows:Identifier>
             <wps:Reference mimeType="image/tiff" xlink:href="http://geoserver/wcs" method="POST">
                   <wps:Body>
                     <wcs:GetCoverage service="WCS" version="1.1.1">
                           <ows:Identifier>geosolutions:dem</ows:Identifier>
                           <wcs:DomainSubset>
                             <gml:BoundingBox crs="http://www.opengis.net/gml/srs/epsg.xml#26713">
                                   <ows:LowerCorner>589980.0 4913700.0</ows:LowerCorner>
                                   <ows:UpperCorner>609000.0 4928010.0</ows:UpperCorner>
                             </gml:BoundingBox>
                           </wcs:DomainSubset>
                           <wcs:Output format="image/tiff"/>
                     </wcs:GetCoverage>
                   </wps:Body>
             </wps:Reference>
           </wps:Input>
           <wps:Input>
             <ows:Identifier>levels</ows:Identifier>
             <wps:Data>
                   <wps:LiteralData>1200</wps:LiteralData>
             </wps:Data>
           </wps:Input>
     </wps:DataInputs>
     <wps:ResponseForm>
           <wps:RawDataOutput mimeType="text/xml; subtype=wfs-collection/1.0">
             <ows:Identifier>result</ows:Identifier>
           </wps:RawDataOutput>
     </wps:ResponseForm>
   </wps:Execute>
   

5. As we did in the wps section cut and paste the XML above into the request.xml file, after having added two more input levels (1200,1400,1600) like below :

   <wps:Execute version="1.0.0" service="WPS" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wps/1.0.0" xmlns:wfs="http://www.opengis.net/wfs" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:wcs="http://www.opengis.net/wcs/1.1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsAll.xsd">
     <ows:Identifier>gs:Contour</ows:Identifier>
     <wps:DataInputs>
           <wps:Input>
             <ows:Identifier>data</ows:Identifier>
             <wps:Reference mimeType="image/tiff" xlink:href="http://geoserver/wcs" method="POST">
                   <wps:Body>
                     <wcs:GetCoverage service="WCS" version="1.1.1">
                           <ows:Identifier>geosolutions:dem</ows:Identifier>
                           <wcs:DomainSubset>
                             <gml:BoundingBox crs="http://www.opengis.net/gml/srs/epsg.xml#26713">
                                   <ows:LowerCorner>589980.0 4913700.0</ows:LowerCorner>
                                   <ows:UpperCorner>609000.0 4928010.0</ows:UpperCorner>
                             </gml:BoundingBox>
                           </wcs:DomainSubset>
                           <wcs:Output format="image/tiff"/>
                     </wcs:GetCoverage>
                   </wps:Body>
             </wps:Reference>
           </wps:Input>
           <wps:Input>
             <ows:Identifier>levels</ows:Identifier>
             <wps:Data>
                   <wps:LiteralData>1200</wps:LiteralData>
             </wps:Data>
           </wps:Input>
           <wps:Input>
             <ows:Identifier>levels</ows:Identifier>
             <wps:Data>
                   <wps:LiteralData>1400</wps:LiteralData>
             </wps:Data>
           </wps:Input>
           <wps:Input>
             <ows:Identifier>levels</ows:Identifier>
             <wps:Data>
                   <wps:LiteralData>1600</wps:LiteralData>
             </wps:Data>
           </wps:Input>
     </wps:DataInputs>
     <wps:ResponseForm>
           <wps:RawDataOutput mimeType="text/xml; subtype=wfs-collection/1.0">
             <ows:Identifier>result</ows:Identifier>
           </wps:RawDataOutput>
     </wps:ResponseForm>
   </wps:Execute>
   

6. Post the request using curl in order to get back the DEM Contour FeatureCollection.

   curl -H "Content-type: xml" -X POST -d@request.xml http://localhost:8083/geoserver/wps -o response.xml