Find a WPS server
Find a data web source that hosts a WPS server, Deltares hosts a test server at http://dtvirt5.deltares.nl/wps/?
Request an overview of the capabilities of a WPS server
Ask for what the server has to offer with a standard WxS GetCapabilities call:
keyword |
value |
source |
|---|---|---|
service |
WPS |
Mandatory WPS standard value |
version |
1.0.0 |
Optional for GetCapabilities |
request |
GetCapabilities |
Mandatory WPS standard value |
language |
Usually 'en' (English) |
Optional |
http://dtvirt5.deltares.nl/wps/? Request=GetCapabilities& Service=WPS
This URL returns an xml file that contains an inventory of the available processes.
Inspect the overview of the content of a WPS server
Look at which WPS processes the server has to offer. For each process there is a tag ows:identifier with an identifier and title of the process, as shown in the reduced xml file example below they are ogrbuffer, constituents, IDT_simple and status_test:
<wps:Capabilities xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" service="WPS" version="1.0.0" xml:lang="en-CA" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsGetCapabilities_response.xsd" updateSequence="1"> <ows:ServiceIdentification> ... </ows:ServiceIdentification> <ows:ServiceProvider> ... </ows:ServiceProvider> ... <ows:HTTP> <ows:Get xlink:href="http://dtvirt5.deltares.nl/wps?"/> <ows:Post xlink:href="http://dtvirt5.deltares.nl/wps"/> </ows:HTTP> ... <wps:ProcessOfferings> <wps:Process wps:processVersion="0.1"> <ows:Identifier>ogrbuffer</ows:Identifier> <ows:Title>Buffer process using OGR</ows:Title> </wps:Process> ... <wps:Process wps:processVersion="1"> <ows:Identifier>constituents</ows:Identifier> <ows:Title>Lookup constituents based on their short name</ows:Title> </wps:Process> <wps:Process wps:processVersion="0.1"> <ows:Identifier>IDT_simple</ows:Identifier> <ows:Title>Interactive Dredge Planning Tool</ows:Title> </wps:Process> <wps:Process wps:processVersion="1"> <ows:Identifier>status_test</ows:Identifier> <ows:Title>echo</ows:Title> <ows:Abstract>Echo server</ows:Abstract> </wps:Process> </wps:ProcessOfferings> ... </wps:Capabilities>
Request a specific process of the WPS server
Where the GetCapabilities request returns a full summary of the server's capatbilities, subsequently the DescribeProcess request can be used to inquire about specific information on a single process:
keyword |
value |
source |
|---|---|---|
service |
WPS |
Mandatory WPS standard value |
version |
1.0.0 |
Mandatory for DescribeProcess |
request |
DescribeProcess |
Mandatory WPS standard value |
identifer |
process name |
Mandatory parameter |
language |
Usually 'en' (English) |
Optional |
In this example we are going to use the constituents process, below the URL for the DescribeProcess request.
http://dtvirt5.deltares.nl/wps/? request=DescribeProcess& service=wps& version=1.0.0& identifier=constituents
This URL will return an xml file that contains a description of the requested processes.
<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://schemas.opengis.net/wps/1.0.0/wpsDescribeProcess_response.xsd" service="WPS" version="1.0.0" xml:lang="en-CA"> <ProcessDescription wps:processVersion="1" storeSupported="false" statusSupported="false"> <ows:Identifier>constituents</ows:Identifier> <ows:Title>Lookup constituents based on their short name</ows:Title> <ows:Abstract> Lookup the speed of the constiuent based on the name of the constituent (following Doodson). </ows:Abstract> <DataInputs> <Input minOccurs="1" maxOccurs="1"> <ows:Identifier>date</ows:Identifier> <ows:Title>Date for which to calculate the nodal factors</ows:Title> <LiteralData> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#string">string</ows:DataType> <ows:AnyValue/> <DefaultValue/> </LiteralData> </Input> <Input minOccurs="1" maxOccurs="1"> <ows:Identifier>constituent</ows:Identifier> <ows:Title>Name of the constituent to look up (M2,...)</ows:Title> <LiteralData> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#string">string</ows:DataType> <ows:AnyValue/> </LiteralData> </Input> <Input minOccurs="1" maxOccurs="1"> <ows:Identifier>nodal</ows:Identifier> <ows:Title>Calculate nodal factors</ows:Title> <LiteralData> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#boolean">boolean</ows:DataType> <ows:AnyValue/> <DefaultValue>False</DefaultValue> </LiteralData> </Input> </DataInputs> <ProcessOutputs> <Output> <ows:Identifier>u</ows:Identifier> <ows:Title>u taken from Schureman</ows:Title> <LiteralOutput> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#float">float</ows:DataType> </LiteralOutput> </Output> <Output> <ows:Identifier>speed</ows:Identifier> <ows:Title>Speed of the constituent (radians per hour)</ows:Title> ... </Output> <Output> <ows:Identifier>FF</ows:Identifier> <ows:Title>FF nodal factor, taken from Schureman</ows:Title> <LiteralOutput> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#float">float</ows:DataType> </LiteralOutput> </Output> <Output> <ows:Identifier>VAU</ows:Identifier> <ows:Title>V+u taken from Schureman</ows:Title> <LiteralOutput> <ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#float">float</ows:DataType> </LiteralOutput> </Output> </ProcessOutputs> </ProcessDescription> </wps:ProcessDescriptions>
In the DescribeProcess document all information about the specific process is given. In the document general information is given in a title and abstract. Besides these also different in- and outputs are defined including titles, datatypes, default values, etc. In the document above we find three different inputs and four different outputs.
Execute a specific process of the WPS server
After finding out the required input parameters for the specific process, subsequently the Execute request can be send:
keyword |
value |
source |
|---|---|---|
service |
WPS |
Mandatory WPS standard value |
version |
1.0.0 |
Mandatory for Execute |
request |
Execute |
Mandatory WPS standard value |
identifer |
process name |
Mandatory parameter |
DataInputs |
inpute parameters |
Mandatory for Execute |
language |
Usually 'en' (English) |
Optional |
Since processes can contain multiple inputs, the DataInputs parameter looks somewhat different. The shape of this parameter is shown below. The different parameters are all after the equal sign (=) of datainputs and between brackets. The different parameters are separated by semicolons (;). Which input parameters are required and how these can be used is found in the DescribeProcess document, at the <ows:identifier> tag the identifier of the input parameter is given, this identifier is used in the URL.
datainputs=[parameter_1=5;parameter_2=9;parameter_3=false]
For the purpose of this example only a single input value will be used in the execute request below.
http://dtvirt5.deltares.nl/wps/? request=Execute& service=wps& version=1.0.0& identifier=constituents& datainputs=[constituent=M2]
The result of the Execute request is an XML document containing the different output parameters with corresponding output values.
<wps:ExecuteResponse 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_response.xsd" service="WPS" version="1.0.0" xml:lang="en-CA" serviceInstance="http://dtvirt5.deltares.nl/wps?service=WPS&request=GetCapabilities&version=1.0.0" statusLocation="http://dtvirt5.deltares.nl/outputwps/pywps-137639971224.xml"> <wps:Process wps:processVersion="1"> <ows:Identifier>constituents</ows:Identifier> <ows:Title>Lookup constituents based on their short name</ows:Title> <ows:Abstract>...</ows:Abstract> </wps:Process> <wps:Status creationTime="2013-08-13T15:15:12Z"> <wps:ProcessSucceeded>PyWPS Process constituents successfully calculated</wps:ProcessSucceeded> </wps:Status> <wps:ProcessOutputs> <wps:Output> <ows:Identifier>u</ows:Identifier> <ows:Title>u taken from Schureman</ows:Title> <wps:Data> <wps:LiteralData dataType="float" uom="None">12.5910330876</wps:LiteralData> </wps:Data> </wps:Output> <wps:Output> <ows:Identifier>speed</ows:Identifier> <ows:Title>Speed of the constituent (radians per hour)</ows:Title> <wps:Data> <wps:LiteralData dataType="float" uom="r">0.505868049939</wps:LiteralData> </wps:Data> </wps:Output> <wps:Output> <ows:Identifier>FF</ows:Identifier> <ows:Title>FF nodal factor, taken from Schureman</ows:Title> <wps:Data> <wps:LiteralData dataType="float" uom="None">1.0281626242</wps:LiteralData> </wps:Data> </wps:Output> <wps:Output> <ows:Identifier>VAU</ows:Identifier> <ows:Title>V+u taken from Schureman</ows:Title> <wps:Data> <wps:LiteralData dataType="float" uom="None">16.2091031443</wps:LiteralData> </wps:Data> </wps:Output> </wps:ProcessOutputs> </wps:ExecuteResponse>
Asking for a specific output format.
The tidal_predict method supports both text/csv and application/json. The available attribute values are in the DescribeProcess xml file.
<wps:ProcessDescriptions ...> <ProcessDescription ...> <ProcessOutputs> <Output><ows:Identifier>tide</ows:Identifier> <ows:Title>Calculated water level for requested locations and date</ows:Title><ComplexOutput> <Default> <Format><MimeType>text/csv</MimeType></Format> </Default> <Supported> <Format><MimeType>text/csv</MimeType></Format> <Format><MimeType>application/json</MimeType></Format> </Supported></ComplexOutput> </Output> </ProcessOutputs> </ProcessDescription> </wps:ProcessDescriptions>
To get the non-default json output instead of the default csv output, add a keyword &responsedocument (outside datainputs brackets), using the WPS standard that you can specify attributes of a something by padding =@attributename=attributename. In this case we add an attribute mimetype=application/json to the output value tide as &responsedocument=tide=@mimetype=application/json, yielding the following url:
<?xml version="1.0" encoding="utf-8"?>
...
http://dtvirt5.deltares.nl/wps?request=Execute&service=wps&version=1.0.0
&identifier=tidal_predict
&datainputs=[location=LINESTRING%282%2052,3%2053%29;
startdate=2020-01-01;
enddate=2020-01-02]
&responsedocument=tide=@mimetype=application/json
Which gives:
<?xml version="1.0" encoding="utf-8"?>
<wps:ExecuteResponse 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_response.xsd" service="WPS" version="1.0.0" xml:lang="en-CA" serviceInstance="http://dtvirt5.deltares.nl/wps?service=WPS&request=GetCapabilities&version=1.0.0">
<wps:Process wps:processVersion="0.1">
<ows:Identifier>tidal_predict</ows:Identifier>
<ows:Title>Tidal prediction tool</ows:Title>
<ows:Abstract>
Tidal prediction tool can be used for different tidal prediction requests.
Prediction is calculated from Topex/Poseidon dataset.
Constitutuents provided by OSU TPXO.
</ows:Abstract>
</wps:Process>
<wps:Status creationTime="2013-08-18T22:22:11Z">
<wps:ProcessSucceeded>PyWPS Process tidal_predict successfully calculated</wps:ProcessSucceeded>
</wps:Status>
<wps:ProcessOutputs>
<wps:Output>
<ows:Identifier>tide</ows:Identifier>
<ows:Title>Calculated water level for requested locations and date</ows:Title>
<wps:Data>
<wps:ComplexData mimeType="application/json">
[{"date":1577836800000000000,"h":0.9055217703,"lat":52.0,"lon":2.0},{"date":1577840400000000000,"h":0.5269456712,"lat":52.0,"lon":2.0},{"date":1577844000000000000,"h":-0.0264890836,"lat":52.0,"lon":2.0},{"date":1577847600000000000,"h":-0.5541336177,"lat":52.0,"lon":2.0},{"date":1577851200000000000,"h":-0.9109530928,"lat":52.0,"lon":2.0},{"date":1577854800000000000,"h":-1.0493201774,"lat":52.0,"lon":2.0},{"date":1577858400000000000,"h":-0.9827940939,"lat":52.0,"lon":2.0},{"date":1577862000000000000,"h":-0.7274707407,"lat":52.0,"lon":2.0},{"date":1577865600000000000,"h":-0.2892092144,"lat":52.0,"lon":2.0},{"date":1577869200000000000,"h":0.2907139097,"lat":52.0,"lon":2.0},{"date":1577872800000000000,"h":0.8872141613,"lat":52.0,"lon":2.0},{"date":1577876400000000000,"h":1.3083130215,"lat":52.0,"lon":2.0},{"date":1577880000000000000,"h":1.3872365816,"lat":52.0,"lon":2.0},{"date":1577883600000000000,"h":1.085052368,"lat":52.0,"lon":2.0},{"date":1577887200000000000,"h":0.5201416491,"lat":52.0,"lon":2.0},{"date":1577890800000000000,"h":-0.1020110267,"lat":52.0,"lon":2.0},{"date":1577894400000000000,"h":-0.6028626472,"lat":52.0,"lon":2.0},{"date":1577898000000000000,"h":-0.9006199205,"lat":52.0,"lon":2.0},{"date":1577901600000000000,"h":-0.9942235126,"lat":52.0,"lon":2.0},{"date":1577905200000000000,"h":-0.8999725194,"lat":52.0,"lon":2.0},{"date":1577908800000000000,"h":-0.6170361442,"lat":52.0,"lon":2.0},{"date":1577912400000000000,"h":-0.1592478845,"lat":52.0,"lon":2.0},{"date":1577916000000000000,"h":0.3852466596,"lat":52.0,"lon":2.0},{"date":1577919600000000000,"h":0.8422715702,"lat":52.0,"lon":2.0},{"date":1577923200000000000,"h":1.0239596024,"lat":52.0,"lon":2.0},{"date":1577836800000000000,"h":0.3589546692,"lat":53.0,"lon":3.0},{"date":1577840400000000000,"h":0.1607531366,"lat":53.0,"lon":3.0},{"date":1577844000000000000,"h":-0.1128007448,"lat":53.0,"lon":3.0},{"date":1577847600000000000,"h":-0.360735561,"lat":53.0,"lon":3.0},{"date":1577851200000000000,"h":-0.5135657472,"lat":53.0,"lon":3.0},{"date":1577854800000000000,"h":-0.5523997776,"lat":53.0,"lon":3.0},{"date":1577858400000000000,"h":-0.488455418,"lat":53.0,"lon":3.0},{"date":1577862000000000000,"h":-0.332647575,"lat":53.0,"lon":3.0},{"date":1577865600000000000,"h":-0.0899128505,"lat":53.0,"lon":3.0},{"date":1577869200000000000,"h":0.2167441457,"lat":53.0,"lon":3.0},{"date":1577872800000000000,"h":0.5221087736,"lat":53.0,"lon":3.0},{"date":1577876400000000000,"h":0.72895627,"lat":53.0,"lon":3.0},{"date":1577880000000000000,"h":0.7560079569,"lat":53.0,"lon":3.0},{"date":1577883600000000000,"h":0.5892076622,"lat":53.0,"lon":3.0},{"date":1577887200000000000,"h":0.2938556551,"lat":53.0,"lon":3.0},{"date":1577890800000000000,"h":-0.0239550777,"lat":53.0,"lon":3.0},{"date":1577894400000000000,"h":-0.276009934,"lat":53.0,"lon":3.0},{"date":1577898000000000000,"h":-0.425450966,"lat":53.0,"lon":3.0},{"date":1577901600000000000,"h":-0.475583489,"lat":53.0,"lon":3.0},{"date":1577905200000000000,"h":-0.4359643097,"lat":53.0,"lon":3.0},{"date":1577908800000000000,"h":-0.3055336229,"lat":53.0,"lon":3.0},{"date":1577912400000000000,"h":-0.0905682739,"lat":53.0,"lon":3.0},{"date":1577916000000000000,"h":0.1642704437,"lat":53.0,"lon":3.0},{"date":1577919600000000000,"h":0.3712641261,"lat":53.0,"lon":3.0},{"date":1577923200000000000,"h":0.4383804482,"lat":53.0,"lon":3.0}]
</wps:ComplexData>
</wps:Data>
</wps:Output>
</wps:ProcessOutputs>
</wps:ExecuteResponse>
The service is validated with the timeseries from live.getij.nl (Dutch tidal information)
