Using WPS 1.0 standard - CNES experience review

HAWG - Frascati, Italy - january 23rd, 2013
Full meeting agenda is here http://goo.gl/uKzqM

The objective of the testbed is to develop a WPS interface to OTB processings and to offer a complete processing chain for remote sensing images including orthorectification, cloud detection and land cover classification...accessible from a web browser

Transcript

1. Using WPS 1.0 standard CNES experience review Jérôme Gasperi | HMA AWG Meeting Frascati - January 23rd, 2013
2. Testbed overview
3. The objective of the testbed is to develop a WPS interface to OTB* processings and to offer a complete processing chain for remote sensing images including orthorectification, cloud detection and land cover classification...accessible from a web browser *Orfeo ToolBox (OTB) is an open source library for remote sensing image processing. The project had been initiated by the French Space Agency (CNES).
4. ORFEO Toolbox http://orfeo-toolbox.org/ "Simple" processes Binary Treshold Sharpening ...etc... Advanced processes Orthorectification Cloud detection Vegetation Indice computation Vectorization Classification ...etc... Constellation http://www.constellation-sdi.org/ WPS interface Client Server http://mapshup.info
5. Web Processing Service WPS 1.0 overview
7. GetCapabilities The GetCapabilities operation p r ov i d e s a c c e s s t o g e n e r a l information about a live WPS implementation, and lists the operations and access methods supported by that implementation Discover 1
8. GetCapabilities The GetCapabilities operation p r ov i d e s a c c e s s t o g e n e r a l information about a live WPS implementation, and lists the operations and access methods supported by that implementation Discover 1 DescribeProcess 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 Describe 2
9. GetCapabilities The GetCapabilities operation p r ov i d e s a c c e s s t o g e n e r a l information about a live WPS implementation, and lists the operations and access methods supported by that implementation Discover 1 DescribeProcess 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 Describe 2 Execute The Execute operation allows WPS clients to run a specified process implemented by a server, using the input parameter values provided and retur ning the output values produced. Inputs can be included directly in the Execute request, or reference web accessible resources Execute 3
10. <wps:Capabilities service="WPS" xml:lang="en-EN" version="1.0.0" updateSequence="1352815432361"> <ows:ServiceIdentification> [...Service information i.e. title, abstract, keywords, etc...] </ows:ServiceIdentification> <ows:ServiceProvider> [...Provider information i.e. name, adress, phone, etc...] </ows:ServiceProvider> <ows:OperationsMetadata> [...URLs to GetCapabilities, DescribeProcess and execute services...] </ows:OperationsMetadata> <wps:ProcessOfferings> <wps:Process wps:processVersion="1.0.0"> <ows:Identifier>urn:ogc:cstl:wps:otb:classification</ows:Identifier> <ows:Title>Classification</ows:Title> <ows:Abstract>Performs an image classification</ows:Abstract> </wps:Process> [...] </wps:ProcessOfferings> <wps:Languages> [...] </wps:Languages> <wps:WSDL xlink:href=""/> </wps:Capabilities> GetCapabilities http://my.server.com/wps?service=WPS&request=GetCapabilities
11. <wps:ProcessDescriptions xmlns:gml="http://www.opengis.net/gml" xmlns:xlink="http://www.w3.org/1999/ xlink" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" service="WPS" version="1.0.0" xml:lang="en-EN"> <ProcessDescription storeSupported="true" statusSupported="true" wps:processVersion="1.0.0"> <ows:Identifier>urn:ogc:cstl:wps:otb:classification</ows:Identifier> <ows:Title>Classification</ows:Title> <ows:Abstract>Performs an image classification</ows:Abstract> <DataInputs> [...Standardized description of ComplexData, LiteralData or BoundingBoxData...] </DataInputs> <ProcessOutputs> [...Standardized description of ComplexOutput, LiteralOutput or BoundingBoxOutput...] </ProcessOutputs> </ProcessDescription> </wps:ProcessDescriptions> DescribeProcess http://my.server.com/wps?service=WPS&request=DescribeProcess&identifier=urn:ogc:cstl:wps:otb:classification storeSupported If true, process execution is launched asynchronously - server acknowledges request and the process is performed in background. Otherwise, process execution is synchronous - server send a response back when process is finished. In this case, the HTTP connection between server and client must remains active otherwise the process result is lost
12. <wps:ExecuteResponse xml:lang="en" service="WPS" serviceInstance="http://mon.serveur.com/wps/wps?" statusLocation="http://mon.serveur.com/wps/wps?request=GetExecutionStatus&executionId=5e59-6dfe" 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"> <wps:Process wps:processVersion="1.0.0"> <ows:Identifier>urn:ogc:cstl:wps:otb:classification</ows:Identifier> <ows:Title>Classification</ows:Title> <ows:Abstract>Performs an image classification</ows:Abstract> </wps:Process> <wps:Status creationTime="2013-01-09T16:17:08.262Z"> <wps:ProcessAccepted>Process accepted</wps:ProcessAccepted> </wps:Status> </wps:ExecuteResponse> Execute http://my.server.com/wps?service=WPS&request=execute POST data + statusLocation The server updates the statusLocation url content according to the progress of the process. When the process is over, the status is set to <wps:ProcessSucceeded> by the server. Therefore, the Web client must regularly call the statusLocation url in order to determine the end of the process
13. Testbed preliminary results
14. https://vimeo.com/57101606
15. Issues Because WPS 1.0 is not perfect :)
16. #1 Asynchronous processes management is not straightforward i.e. storeExecute boolean attribute; no formal GetStatus operation Once launched, there is no possibility to modify the process execution (i.e. no pause, resume or abort operations)
17. #1 Asynchronous processes management is not straightforward i.e. storeExecute boolean attribute; no formal GetStatus operation Once launched, there is no possibility to modify the process execution (i.e. no pause, resume or abort operations) This issue will be handled in WPS 2.0
18. Issue #2 How do i know that only Polygon is supported ? Issue #3 How do i link each polygon with the right class ? One solution is to define a Feature including both geometry and classification type...but this is quite complex to handle on client side. Alternative solution is to define Inputs groups. This is not supported by WPS 1.0 <DataInputs> <Input minOccurs="1" maxOccurs="99"> <ows:Identifier>geom</ows:Identifier> <ows:Title>Polygon</ows:Title> <ows:Abstract>Input polygon</ows:Abstract> <ComplexData> <Default> <Format> <MimeType>text/xml; subtype=gml/3.1.1</MimeType> </Format> </Default> </ComplexData> </Input> <Input minOccurs="1" maxOccurs="99"> <ows:Identifier>type</ows:Identifier> <ows:Title>Class type</ows:Title> <ows:Abstract>Input classification type</ows:Abstract> <LiteralData> <ows:AllowedValues> <ows:Value>Water</ows:Value> <ows:Value>Forest</ows:Value> <ows:Value>Cropland</ows:Value> ... </ows:AllowedValues> </LiteralData> </Input> </DataInputs> #2 #3 & Use case : In "assisted classification" mode, user needs to define 1...n polygons of [water, forest, cropland, etc.] as input
19. Asynchronous process response document is available at statusLocation url. There is no way for the server to tell the client how long this url will be valid (hours, months, years, etc. ?) - and no way to know how long the result url within the response document will be valid too... #4
20. Summary
22. WPS 1.0 specification is simple and readable !
23. WPS 1.0 specification is simple and readable ! Easy to implement on server. A bit more tricky on the client side due to inputs genericity (e.g. GML features)
24. WPS 1.0 specification is simple and readable ! Easy to implement on server. A bit more tricky on the client side due to inputs genericity (e.g. GML features) It is a Web service technology so it is naturally made for the cloud
25. WPS 1.0 specification is simple and readable ! Easy to implement on server. A bit more tricky on the client side due to inputs genericity (e.g. GML features) It is a Web service technology so it is naturally made for the cloud Limitations with asynchronous processes in WPS 1.0 will be handled in WPS 2.0
26. jerome.gasperi@cnes.fr