Geospatial Data Processing

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Contents

Overview

Geospatial Data Processing takes advantage of the OGC Web Processing Service (WPS) as web interface to allow for the dynamic deployment of user processes. In this case, Terradue selected the 52° North WPS open source component, as the interface to a Cloud service that we developed to allow the deployment of user “algorithms”. We demonstrate that such user algorithms can be developed to exploit the powerful and distributed framework offered by Apache™ Hadoop™ MapReduce. The source code for wrappers and examples developed by Terradue are contributed via the iMarine EC FP7 project to the D4Science gCube infrastructure components.

Thus was born WPS-Hadoop.

Key Features

WPS-Hadoop offers a web interface to access the algorithms from external HTTP clients through three different kind of requests, made available through the Web Processing Standard interface:

  • The GetCapabilities operation provides access to general information about a live WPS implementation, and lists the operations and access methods supported by that implementation. 52N WPS supports the GetCapabilities operation via HTTP GET and POST.
  • The DescribeProcess operation allows WPS clients to request a full description of one or more processes that can be executed by the service. This description includes the input and output parameters and formats and can be used to automatically build a user interface to capture the parameter values to be used to execute a process.
  • The Execute operation allows WPS clients to run a specified process implemented by the server, using the input parameter values provided and returning the output values produced. Inputs can be included directly in the Execute request, or reference web accessible resources.

Design

Extending the AbstractAlgorithm class (by 52N) we have created a new abstract class called HadoopAbstractAlgorithm where the Business Logic, hidden to the developer, is used to execute the process creating a Job for the Hadoop framework.

Image:blocks.png

Develop a custom process

The custom process class has to extend HadoopAbstractAlgorithm which allows you to specify the Hadoop Configuration parameters (e.g. from XML files), the Mapper and Reducer classes, Input Paths, Output Path, all the operations needed before to run the process and the way to retrieve the results. By using HadoopAbstractAlgorithm, you need to fill these simple methods:

  • protected Class<? extends Mapper<?, ?, LongWritable, Text>> getMapper()

This method returns the class to be used as Mapper;

  • protected Class<? extends Reducer<LongWritable, Text, ?, ?>> getReducer()

This method returns the class to be used as Reducer (if exists);

  • protected Path[] getInputPaths(Map<String, List<IData>> inputData)

This method allows to the business logic to know the exact input path(s) to pass to the Hadoop framework;

  • protected String getOutputPath()

This method allows to the business logic to know the exact output path to pass to the Hadoop framework;

  • protected Map buildResults()

This method is called by the business logic method to pass build output that the WPS does expect;

  • public void prepareToRun(Map<String, List<IData>> inputData)

This method has to be filled by all the operations to do before to run the Hadoop Job (e.g. WPS input validation);

  • protected JobConf getJobConf()

This method allows the user to specify all the configuration resources for (from) Hadoop framework (e.g. XML conf files).

Image:HadoopAbstractAlgorithm.png

Deploy custom process

WPS-hadoop is deployed over Tomcat container.

In order to deploy the recently developed process, you need to:

  1. Export in a jar file the process.
  2. Copy the exported lib into the WEB-INF/lib directory.
  3. Restart tomcat.
    Next, we need to register the newly created algorithm:
  4. Go to http://localhost:yourport/wps/ , e.g.http://localhost:8080/wps/.
  5. Click on 52n WPSAdmin console.
  6. Login with:
    • Username: wps
    • Password: wps
    The Web Admin Console lets you change the basic configuration of the WPS and upload processes.
  7. Click on Algorithm Repository --> Properties (the '+' sign).
  8. Click on the Green '+' to register your process: Type in the left field Algorithm and in the right field the fully qualified class name of your created class (i.e. package + class name, e.g. org.n52.wps.demo.ConvexHullDemo).
  9. Click on the save icon (the 'disk').
  10. Next, Click on the top left on 'Save and Activate configuration'.
  11. Your new Process is now available, test it under: http://localhost:yourport/wps/WebProcessingService?Request=GetCapabilities&Service=WPS or directly http://localhost:yourport/wps/test.hmtl.


N.B. Alternatively to the step 1. you can follow steps 4. , 5. and 6. first, then click on Upload Process and pick the .java file of your just developed process. Then follow from step 2 onwards.

Some complete examples

The Bathymetry Algorithm

Here is a complete description of the use of WPS-hadoop library, through the example of Bathymetry retrieving from a netCDF file. An input file containing a series of coordinate pairs will generate a file of "z" (bathymetry) value for the given x,y pair.


Class Diagram

BathymetryAlgorithm.xml

This file must be named exactly like the .java one.

<?xml version="1.0" encoding="UTF-8"?>
<wps:ProcessDescriptions xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
http://geoserver.itc.nl:8080/wps/schemas/wps/1.0.0/wpsDescribeProcess_response.xsd" xml:lang="en-US" service="WPS" version="1.0.0">
        <ProcessDescription wps:processVersion="1.0.0" storeSupported="true" statusSupported="false">
                <ows:Identifier>com.terradue.wps.BathymetryAlgorithm</ows:Identifier>
                <ows:Title>Bathymetry Algorithm</ows:Title>
                <ows:Abstract>by Hadoop</ows:Abstract>
                <ows:Metadata xlink:title="Bathymetry" />
                <DataInputs>
                         <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>coordinates</ows:Identifier>
                                <ows:Title>coordinatesFile</ows:Title>
                                <ows:Abstract>URL to a file containing x,y parameters</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>InputFile</ows:Identifier>
                                <ows:Title>InputFile</ows:Title>
                                <ows:Abstract>URL to the file netCDF</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                </DataInputs>
                <ProcessOutputs>
                        <Output>
                                <ows:Identifier>result</ows:Identifier>
                                <ows:Title>result</ows:Title>
                                <ows:Abstract>result</ows:Abstract>
                                <LiteralOutput>
                                        <ows:DataType ows:reference="xs:string"/>
                                </LiteralOutput>
                        </Output>
                </ProcessOutputs>
        </ProcessDescription>
</wps:ProcessDescriptions>

Requests examples

This is an example of how to request the execution of the BathymetryAlgorithm.

XML request example

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<wps:Execute service="WPS" version="1.0.0" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" 
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
    http://schemas.opengis.net/wps/1.0.0/wpsExecute_request.xsd">
    <ows:Identifier>com.terradue.wps_hadoop.examples.bathymetry.BathymetryAlgorithm</ows:Identifier>
    <wps:DataInputs>
        <wps:Input>
            <ows:Identifier>coordinates</ows:Identifier>
            <ows:Title>Coordinates file for Bathymetry</ows:Title>
            <wps:Data>
                <wps:LiteralData>http://t2-10-11-30-97.play.terradue.int:8888/wps/maps/coordinates</wps:LiteralData>
            </wps:Data>
        </wps:Input>
        <wps:Input>
            <ows:Identifier>InputFile</ows:Identifier>
            <ows:Title>netCDF file for Bathymetry</ows:Title>
            <wps:Data>
                <wps:LiteralData>http://opendap.deltares.nl/thredds/fileServer/opendap/deltares/delftdashboard/bathymetry/gebco_08/gebco08.nc</wps:LiteralData>
            </wps:Data>
        </wps:Input>
    </wps:DataInputs>
    <wps:ResponseForm>
    <wps:ResponseDocument storeExecuteResponse="false">
        <wps:Output asReference="false">
            <ows:Identifier>result</ows:Identifier>
        </wps:Output>
    </wps:ResponseDocument>
    </wps:ResponseForm>
</wps:Execute>

Input parameter description

InputFile: This file contains a series of x,y (-180< x < 180 and -90 < y < 90) pairs. Every file's line will be taking over from a single mapper instance. This is the InputFile required format:

xa1 ya1 xa2 ya2 xa3 ya3 xa4 ya4...xan yan
xb1 yb1 xb2 yb2 xb3 yb3 xb4 yb4...xbm ybm
.
.
.
 

KVP (Key Value Pairs) request example

http://t2-10-11-30-97.play.terradue.int:8888/wps/WebProcessingService?Request=Execute&service=WPS&version=1.0.0&language=en-CA&Identifier=com.terradue.wps_hadoop.examples.bathymetry.BathymetryAlgorithm&DataInputs=coordinates=http://10.11.30.97:8888/wps/maps/coordinates;InputFile=http://opendap.deltares.nl/thredds/fileServer/opendap/deltares/delftdashboard/bathymetry/gebco_08/gebco08.nc

Resampler Algorithm

Class Diagram

ResamplerAlgorithm.xml

<?xml version="1.0" encoding="UTF-8"?>
<wps:ProcessDescriptions xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
http://geoserver.itc.nl:8080/wps/schemas/wps/1.0.0/wpsDescribeProcess_response.xsd" xml:lang="en-US" service="WPS" version="1.0.0">
        <ProcessDescription wps:processVersion="1.0.0" storeSupported="true" statusSupported="false">
                <ows:Identifier>com.terradue.wps_hadoop.examples.resampler.ResamplerAlgorithm</ows:Identifier>
                <ows:Title>Resampler Algorithm</ows:Title>
                <ows:Abstract>by Hadoop</ows:Abstract>
                <ows:Metadata xlink:title="resampler" />
                <DataInputs>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>wcs_url</ows:Identifier>
                                <ows:Title>wcs_url</ows:Title>
                                <ows:Abstract>wcs_url</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>resolution</ows:Identifier>
                                <ows:Title>resolution</ows:Title>
                                <ows:Abstract>resolution</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                </DataInputs>
                <ProcessOutputs>
                        <Output>
                                <ows:Identifier>result</ows:Identifier>
                                <ows:Title>result</ows:Title>
                                <ows:Abstract>result</ows:Abstract>
                                <LiteralOutput>
                                        <ows:DataType ows:reference="xs:string"/>
                                </LiteralOutput>
                        </Output>
                </ProcessOutputs>
        </ProcessDescription>
</wps:ProcessDescriptions>

Requests examples

This is an example of how to request the execution of the ResamplerAlgorithm.

XML request example

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<wps:Execute service="WPS" version="1.0.0" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" 
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
    http://schemas.opengis.net/wps/1.0.0/wpsExecute_request.xsd">
    <ows:Identifier>com.terradue.wps_hadoop.examples.resampler.ResamplerAlgorithm</ows:Identifier>
    <wps:DataInputs>
        <wps:Input>
            <ows:Identifier>wcs_url</ows:Identifier>
            <ows:Title>WCS product's URL to be resampled</ows:Title>
            <wps:Data>
                <wps:LiteralData>http://t2-10-11-30-98.play.terradue.int:8080/thredds/wcs/maps/SST_MED_SST_L4_NRT_OBSERVATIONS_010_004_c_2011-11-03_2011-11-04.nc
                ?service=WCS&version=1.0.0&request=GetCoverage&COVERAGE=analysed_sst&bbox=-18,20,36,45&width=100&height=100&format=geotiff</wps:LiteralData>
            </wps:Data>
        </wps:Input>
        <wps:Input>
            <ows:Identifier>wcs_url</ows:Identifier>
            <ows:Title>WCS product's URL to be resampled (in degrees)</ows:Title>
            <wps:Data>
                <wps:LiteralData>0.01666923868312760</wps:LiteralData>
            </wps:Data>
        </wps:Input>
    </wps:DataInputs>
    <wps:ResponseForm>
    <wps:ResponseDocument storeExecuteResponse="false">
        <wps:Output asReference="false">
            <ows:Identifier>result</ows:Identifier>
        </wps:Output>
    </wps:ResponseDocument>
    </wps:ResponseForm>
</wps:Execute>

Input parameter description

wcs_url: This should be an URL to a WCS to be queried to get a Coverage;

resolution: This is the desired resolution in degrees for the downloaded Coverage.

KVP (Key Value Pairs) request example

http://t2-10-11-30-97.play.terradue.int:8888/wps/WebProcessingService?Request=Execute&service=WPS&version=1.0.0&language=en-CA&Identifier=com.terradue.wps_hadoop.examples.resampler.ResamplerAlgorithm&DataInputs=wcs_url=http://t2-10-11-30-98.play.terradue.int:8080/thredds/wcs/maps/SST_MED_SST_L4_NRT_OBSERVATIONS_010_004_c_2011-11-03_2011-11-04.nc?service=WCS&version=1.0.0&request=GetCoverage&COVERAGE=analysed_sst&bbox=-18,20,36,45&width=100&height=100&format=geotiff;resolution=0.01666923868312760

Before to submit this kind of request you need to encode it in this way:

http://t2-10-11-30-97.play.terradue.int:8888/wps/WebProcessingService?Request=Execute&service=WPS&version=1.0.0&language=en-CA&Identifier=com.terradue.wps_hadoop.examples.resampler.ResamplerAlgorithm&DataInputs=wcs_url=http://t2-10-11-30-98.play.terradue.int:8080/thredds/wcs/maps/SST_MED_SST_L4_NRT_OBSERVATIONS_010_004_c_2011-11-03_2011-11-04.nc?service=WCS%25version=1.0.0%25request=GetCoverage%25COVERAGE=analysed_sst%25bbox=-18,20,36,45%25width=100%25height= 100%25format=geotiff;resolution=0.01666923868312760


More information

In order to exploit the real potential of Hadoop, more than a request should be sent to the WPS concurrently.

Intersection Algorithm

Class Diagram

IntersectionHadoopAlgorithm.xml

<?xml version="1.0" encoding="UTF-8"?>
<wps:ProcessDescriptions xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
http://geoserver.itc.nl:8080/wps/schemas/wps/1.0.0/wpsDescribeProcess_response.xsd" xml:lang="en-US" service="WPS" version="1.0.0">
        <ProcessDescription wps:processVersion="1.0.0" storeSupported="true" statusSupported="false">
                <ows:Identifier>com.terradue.wps_hadoop.examples.IntersectionAlgorithm</ows:Identifier>
                <ows:Title>Intersection Algorithm</ows:Title>
                <ows:Abstract>Calculate Intersection Feature</ows:Abstract>
                <ows:Metadata xlink:title="Intersection" />
                <DataInputs>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>Polygon1</ows:Identifier>
                                <ows:Title>Polygon1</ows:Title>
                                <ows:Abstract>Polygon 1 URL</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>Polygon2</ows:Identifier>
                                <ows:Title>Polygon2</ows:Title>
                                <ows:Abstract>Polygon 2 URL</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                </DataInputs>
                <ProcessOutputs>
                        <Output>
                                <ows:Identifier>result</ows:Identifier>
                                <ows:Title>result</ows:Title>
                                <ows:Abstract>result</ows:Abstract>
                                <LiteralOutput>
                                        <ows:DataType ows:reference="xs:string"/>
                                </LiteralOutput>
                        </Output>
                </ProcessOutputs>
        </ProcessDescription>
</wps:ProcessDescriptions>

Requests examples

This is an example of how to request the execution of the ResamplerAlgorithm.

XML request example

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<wps:Execute service="WPS" version="1.0.0" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" 
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
    http://schemas.opengis.net/wps/1.0.0/wpsExecute_request.xsd">
    <ows:Identifier>com.terradue.wps_hadoop.examples.intersection.IntersectionHadoopAlgorithm</ows:Identifier>
    <wps:DataInputs>
        <wps:Input>
            <ows:Identifier>Polygon1</ows:Identifier>
            <ows:Title>First polygon to be intersected</ows:Title>
            <wps:Data>
                <wps:LiteralData>http://www.fao.org/figis/geoserver/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=fifao:FAO_MAJOR&CQL_FILTER=fifao:F_AREA=21</wps:LiteralData>
            </wps:Data>
        </wps:Input>
        <wps:Input>
            <ows:Identifier>Polygon2</ows:Identifier>
            <ows:Title>Second Polygon to be intersected</ows:Title>
            <wps:Data>
                <wps:LiteralData>http://geo.vliz.be/geoserver/Marbound/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=Marbound:eez&CQL_FILTER%3DINTERSECTS%28Marbound%3Athe_geom%2CPOLYGON%28%28-82.410003662+34.830001831%2C-42+34.830001831%2C-42+78.166666031%2C-82.410003662+78.166666031%2C-82.410003662+34.830001831%29%29%29</wps:LiteralData>
            </wps:Data>
        </wps:Input>
    </wps:DataInputs>
    <wps:ResponseForm>
    <wps:ResponseDocument storeExecuteResponse="false">
        <wps:Output asReference="false">
            <ows:Identifier>result</ows:Identifier>
        </wps:Output>
    </wps:ResponseDocument>
    </wps:ResponseForm>
</wps:Execute>


Input parameter description

Polygon1 and Polygon2: URLs to some WFS where to get two features containing valid geometries.

KVP (Key Value Pairs) request example

http://t2-10-11-30-97.play.terradue.int:8888/wps/WebProcessingService?Request=Execute&service=WPS&version=1.0.0&language=en-CA&Identifier=com.terradue.wps_hadoop.examples.intersection.IntersectionHadoopAlgorithm&DataInputs=Polygon1=http://www.fao.org/figis/geoserver/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=fifao:FAO_MAJOR&CQL_FILTER=fifao:F_AREA=21;Polygon2=http://geo.vliz.be/geoserver/Marbound/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=Marbound:eez&CQL_FILTER%3DINTERSECTS%28Marbound%3Athe_geom%2CPOLYGON%28%28-82.410003662+34.830001831%2C-42+34.830001831%2C-42+78.166666031%2C-82.410003662+78.166666031%2C-82.410003662+34.830001831%29%29%29

Before to submit this kind of request you need to encode it in this way:

http://localhost:8888/wps/WebProcessingService?Request=Execute&service=WPS&version=1.0.0&language=en-CA&Identifier=com.terradue.wps_hadoop.examples.intersection.IntersectionHadoopAlgorithm&DataInputs=Polygon1=http%3A%2F%2Fwww.fao.org%2Ffigis%2Fgeoserver%2Fows%3Fservice%3DWFS%26version%3D1.0.0%26request%3DGetFeature%26typeName%3Dfifao%3AFAO_MAJOR%26CQL_FILTER%3Dfifao%3AF_AREA%3D21;Polygon2=http%3A%2F%2Fgeo.vliz.be%2Fgeoserver%2FMarbound%2Fows%3Fservice%3DWFS%26version%3D1.0.0%26request%3DGetFeature%26typeName%3DMarbound%3Aeez%26CQL_FILTER=INTERSECTS%28Marbound%3Athe_geom%2CPOLYGON%28%28-82.410003662+34.830001831%2C-42+34.830001831%2C-42+78.166666031%2C-82.410003662+78.166666031%2C-82.410003662+34.830001831%29%29%29


More information

This algorithm is the adaption to WPS-hadoop framework of the original IntersectionAlgorithm developed by 52North. This template was sent and discussed with FAO (Emmanuel Blondel) to be improved by the community according to their requirements (e.g. area of the intersections).


TIFFUploader Algorithm

Overview

Another algorithm was developed to create a visualization library that exploits a Geoserver WMS (Web Map Service) by uploading a file netCDF as a new Workspace and its bands as new layers.

Class Diagram

Geotiff Uploader library

TiffUploader algorithm is based on GDAL native library due to a software developed by Terradue called GeoTIFF Uploader, that uses a Java bind library . After downloaded a netCDF file on the local filesystem, Geotiff Uploader splits it in as many GeoTIFF files as the number of data bands. Finally the library upload these files as layers of a new Workspace just created from the netCDF file itself, on the Geoserver instance. The control returns to the WPSHadoop algorithm.

Release note: since Geotiff Uploader is based on GDAL Java bind, it needs to be delivered with the right dependencies, according with the architecture that will run the application. For this purpose, multiple Maven profiles where created, each for the most popular architectures:

  • linux-i386
  • linux-x86_64
  • mac-x86_64

TIFFUploaderAlgorithm.xml

<?xml version="1.0" encoding="UTF-8"?>
<wps:ProcessDescriptions xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0
http://geoserver.itc.nl:8080/wps/schemas/wps/1.0.0/wpsDescribeProcess_response.xsd" xml:lang="en-US" service="WPS" version="1.0.0">
        <ProcessDescription wps:processVersion="1.0.0" storeSupported="true" statusSupported="false">
                <ows:Identifier>com.terradue.wps.ResamplerAlgorithm</ows:Identifier>
                <ows:Title>TIFF Uploader Algorithm</ows:Title>
                <ows:Abstract>by Hadoop</ows:Abstract>
                <ows:Metadata xlink:title="TIFF Uploader " />
                <DataInputs>
                        <Input minOccurs="1" maxOccurs="1">
                                <ows:Identifier>InputFile</ows:Identifier>
                                <ows:Title>Input FIle</ows:Title>
                                <ows:Abstract>Input file containg references to netCDF resources</ows:Abstract>
                                <LiteralData>
                                        <ows:DataType ows:reference="xs:string"></ows:DataType>
                                        <ows:AnyValue/>
                                </LiteralData>
                        </Input>
                </DataInputs>
                <ProcessOutputs>
                        <Output>
                                <ows:Identifier>result</ows:Identifier>
                                <ows:Title>result</ows:Title>
                                <ows:Abstract>result</ows:Abstract>
                                <LiteralOutput>
                                        <ows:DataType ows:reference="xs:string"/>
                                </LiteralOutput>
                        </Output>
                </ProcessOutputs>
        </ProcessDescription>
</wps:ProcessDescriptions>

Input/Output description

The input for this WPSHadoop algorithm, called InputFile, is a file containing a list of URLs to netCDF files. These files are locally stored before to be splitted into as many new GeoTIFF files as the bands included in the input files. Any line of the InputFile is processed by a separated instance of the mapper. At the end of all the processes, a GetCapabilities request is sent to the Geoserver instance and its answer is used as output (by reference) of the whole WPS process.

The generic WPS-Hadoop Client

Overview

In order to better test both the present and future Algorithms, Terradue developed a simple Java WPS-Client. It also will be very useful to allow external services/client to exploit WPS side of projects. This client is based on the 52 North Java Client API, containing some convenient classes to interact with WPS. In the package called "demo", you can find a usage example of this client with the IntersectionAlgorithm.

Below in detail some snippets from this class.

GetCapabilities

This section shows you how you can request a WPS Capabilities document and how to handle the response.

public CapabilitiesDocument requestGetCapabilities(String url)
			throws WPSClientException {
 
		WPSClientSession wpsClient = WPSClientSession.getInstance();
 
		wpsClient.connect(url);
 
		CapabilitiesDocument capabilities = wpsClient.getWPSCaps(url);
 
		ProcessBriefType[] processList = capabilities.getCapabilities()
				.getProcessOfferings().getProcessArray();
 
		for (ProcessBriefType process : processList) {
			System.out.println(process.getIdentifier().getStringValue());
		}
		return capabilities;
	}

DescribeProcess

This section shows you how you can request a WPS DescribeProcess document and how to handle the response.

public ProcessDescriptionType requestDescribeProcess(String url,
			String processID) throws IOException {
 
		WPSClientSession wpsClient = WPSClientSession.getInstance();
 
		ProcessDescriptionType processDescription = wpsClient
				.getProcessDescription(url, processID);
 
		InputDescriptionType[] inputList = processDescription.getDataInputs()
				.getInputArray();
 
		for (InputDescriptionType input : inputList) {
			System.out.println(input.getIdentifier().getStringValue());
		}
		return processDescription;
	}

Execute

This section shows you how you can execute a WPS process and how to handle the response (in the case of IntersectionAlgorithm). The execution is a bit more complicated than the GetCapabilities and DescribeProcess operations.

	public ExecuteResponseAnalyser executeProcess(String url, String processID,
			ProcessDescriptionType processDescription,
			HashMap<String, Object> inputs) throws Exception {
		ExecuteRequestBuilder executeBuilder = new ExecuteRequestBuilder(
				processDescription);
 
		for (InputDescriptionType input : processDescription.getDataInputs()
				.getInputArray()) {
			String inputName = input.getIdentifier().getStringValue();
			Object inputValue = inputs.get(inputName);
			if (input.getLiteralData() != null) {
				if (inputValue instanceof String) {
					executeBuilder.addLiteralData(inputName,
							(String) inputValue);
				}
			} else if (input.getComplexData() != null) {
				// Complexdata by value
				if (inputValue instanceof FeatureCollection) {
					IData data = new GTVectorDataBinding(
							(FeatureCollection) inputValue);
					executeBuilder
							.addComplexData(
									inputName,
									data,
									"http://schemas.opengis.net/gml/3.1.1/base/feature.xsd",
									"UTF-8", "text/xml");
				}
				// Complexdata Reference
				if (inputValue instanceof String) {
					executeBuilder
							.addComplexDataReference(
									inputName,
									(String) inputValue,
									"http://schemas.opengis.net/gml/3.1.1/base/feature.xsd",
									"UTF-8", "text/xml");
				}
 
				if (inputValue == null && input.getMinOccurs().intValue() > 0) {
					throw new IOException("Property not set, but mandatory: "
							+ inputName);
				}
			}
		}
		executeBuilder.setMimeTypeForOutput("text/xml", "result");
		executeBuilder.setSchemaForOutput(
				"http://schemas.opengis.net/gml/3.1.1/base/feature.xsd",
				"result");
		ExecuteDocument execute = executeBuilder.getExecute();
		execute.getExecute().setService("WPS");
		WPSClientSession wpsClient = WPSClientSession.getInstance();
		Object responseObject = wpsClient.execute(url, execute);
		if (responseObject instanceof ExecuteResponseDocument) {
			ExecuteResponseDocument response = (ExecuteResponseDocument) responseObject;
			ExecuteResponseAnalyser analyser = new ExecuteResponseAnalyser(
					execute, response, processDescription);
			IData data = (IData) analyser.getComplexDataByIndex(0,
					GTVectorDataBinding.class);
			return /*data*/analyser;
		}
		throw new Exception("Exception: " + responseObject.toString());
	}


Main method

Finally this section shows you how to initialize all the Input Data and call the methods described above.

public void testExecute() {
		//Define the wps URL to query
		String wpsURL = "http://10.11.30.97:8888/wps/WebProcessingService";
		//Define the ID (name of the class) of the Process to query
		String processID = "com.terradue.wps_hadoop.examples.intersection.IntersectionHadoopAlgorithm";
 
		try {
			//Example of DescribeProcess request
			ProcessDescriptionType describeProcessDocument = requestDescribeProcess(
					wpsURL, processID);
			System.out.println(describeProcessDocument);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		try {
			//GetCapabilities request 
			CapabilitiesDocument capabilitiesDocument = requestGetCapabilities(wpsURL);
			//DescribeProcess request
			ProcessDescriptionType describeProcessDocument = requestDescribeProcess(
					wpsURL, processID);
			// define inputs
			HashMap<String, Object> inputs = new HashMap<String, Object>();
			// input parameters
			inputs.put(
					"Polygon1",
					"http://www.fao.org/figis/geoserver/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=fifao:FAO_MAJOR&CQL_FILTER=fifao:F_AREA=21");			// literal data
			inputs.put(
					"Polygon2", 
					"http://geo.vliz.be/geoserver/Marbound/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=Marbound:eez&CQL_FILTER%3DINTERSECTS(Marbound%3Athe_geom%2CPOLYGON((-82.410003662+34.830001831%2C-42+34.830001831%2C-42+78.166666031%2C-82.410003662+78.166666031%2C-82.410003662+34.830001831)))");
			//Execute the request
			ExecuteResponseAnalyser analyser = executeProcess(wpsURL, processID,
					describeProcessDocument, inputs);
 
			System.out.println(analyser.getRawResponseDocument().toString());
			//If you are interested to the Data part of the response...
			IData data = (IData) analyser.getComplexDataByIndex(0,GTVectorDataBinding.class);
 
			if (data == null) {
				data = new LiteralStringBinding (analyser.getLiteralDataByIndex(0).getStringValue());
				System.out.println("result "  + data.getPayload());
			}
 
		} catch (WPSClientException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

Client through Command Line interface

A way more generic to use this client, is to invoke it through a Command Line, also provided in the package. This is the usage description of the tool:

 Usage: wpsclient [options]
  Options:
    -I, --INPUT          WPS input parameter(s).
                         Syntax: -Ikey=value
                         Default: {}
    -a, --asynchronous   Set the execution as asynchronous.
                         Default: false
    -c, --capabilities   Display WPS GetCapabilities.
                         Default: false
    -d, --describe       Display DescribeProcess for a given process ID.
                         Default: false
    -e, --execute        Execute the given process ID with the eventually given
                         parameter(s).
                         Default: false
    -f, --file           Path to a file where to write the WPS output.
    -h, --help           Display help informations.
                         Default: false
    -p, --process        The process ID to be used.
    -t, --time           Set the polling interval, in case of asynchronous
                         execution, in milliseconds.
                         Default: 2000
    -u, --url            The WPS url (e.g.
                         "http://localhost:8080/wps/WebProcessingService").


here is an example of how to use this binary:

bin/wpsclient -e -u http://localhost:8080/wps/WebProcessingService /
-p com.terradue.wps_hadoop.examples.intersection.IntersectionAlgorithm /
-IPolygon1=http://www.fao.org/figis/geoserver/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=fifao:FAO_MAJOR&CQL_FILTER=fifao:F_AREA=21 /
-IPolygon2=http://geo.vliz.be/geoserver/Marbound/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=Marbound:eez&CQL_FILTER%3DINTERSECTS(Marbound%3Athe_geom%2CPOLYGON((-82.410003662+34.830001831%2C-42+34.830001831%2C-42+78.166666031%2C-82.410003662+78.166666031%2C-82.410003662+34.830001831)))

In case of array of input (that in WPS must have the same identifiers) use the ',' to separate the input values.

Example:

-IParam=param1,param2

Supported processes

Legacy applications integration

Terradue also provided a Best Practice for Legacy applications integration, as a procedure allowing to capitalize on existing processors / scientific algorithms to be deployed within a WPS-Hadoop computing environment.

Simple R example

IRD provided a simple R example to run under WPS-hadoop. It is described with a Simple_R_example

Kernel density

IRD provided the kernel density estimation from occurrences. The process is described here kernel_density

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