wiki:PetascopeUserGuide

Version 19 (modified by pcampalani, 4 years ago) (diff)

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Petascope User guide

The petascope component of rasdaman implements the OGC interface standards WCS 2.0, WCS-T 1.4, WCPS 1.0, and WPS 1.0. For this purpose, petascope maintains its additional metadata (such as georeferencing) which is kept in separate relational tables. Note that not all rasdaman raster objects and collections are available through petascope by default; rather, they need to be registered through the petascope administration interface.

Petascope is implemented as a war file of servlets which give access to coverages (in the OGC sense) stored in rasdaman. Internally, incoming requests requiring coverage evaluation are translated into rasql queries by petascope. These queries are passed on to rasdaman, which constitutes the central workhorse. Results returned from rasdaman are forwarded to the client, finally.

Miscellanea

  • For the installation, a .war file needs to be deployed and configured for use with some rasdaman server installation. See the installation section? for details.
  • For a developer's introduction to petascope, see the presentation and the related developer guide.
  • For the interpretation of subsets in petascope, see this page.
  • For the handling of time:
    • [rasdaman <= 8.4] see [PetascopeTimeHandling84 this page];
    • [rasdaman >= 9.0] see outlook here.

WCS

"The OpenGIS Web Coverage Service Interface Standard (WCS) defines a standard interface and operations that enables interoperable access to geospatial coverages." (WCS standards)

Petascope supports WCS 2.0; see this demo.

WCPS

"The OpenGIS Web Coverage Service Interface Standard (WCS) defines a protocol-independent language for the extraction, processing, and analysis of multi-dimensional gridded coverages representing sensor, image, or statistics data. Services implementing this language provide access to original or derived sets of geospatial coverage information, in forms that are useful for client-side rendering, input into scientific models, and other client applications. Further information about WPCS can be found at the WCPS Service page of the OGC Network. (http://www.opengeospatial.org/standards/wcps)

The WCPS language is independent from any particular request and response encoding, allowing embedding of WCPS into different target service frameworks like WCS and WPS. The following documents are relevant for WCPS; they can be downloaded from www.opengeospatial.org/standards/wcps:

  • OGC 08-068r2: The protocol-independent ("abstract") syntax definition; this is the core document. Document type: IS (Interface Standard.
  • OGC 08-059r3: This document defines the embedding of WCPS into WCS by specifying a concrete protocol which adds an optional ProcessCoverages? request type to WCS. Document type: IS (Interface Standard.
  • OGC 09-045: This draft document defines the embedding of WCPS into WPS as an application profile by specifying a concrete subtype of the Execute request type.

There is a demo sandbox and demo video; see also the WCPS manual and tutorial.

The petascope implementation supports both XML and Abstract Syntax.

  • To send a abstract syntax request: A post request must be sent. The query string must be sent in a post parameter named query.
  • To send a request as a XML file, a multi-part post request must be sent. Only one file must be sent. The Mime type has to be text/xml.
  • To send a request as XML: A post request must be sent. A post parameter named xml must be attached.

If you intend to implement forms-based access: To obtain a proper query from an XML page a form must be used. The method should be post and action should be an URL pointing to the servlet access point. The form should contain either a file field or a text/hidden field that has the name xml or query. An error in the access method will generate an HTML query input form.

WPS

"The OpenGIS Web Processing Service (WPS) Interface Standard provides rules for standardizing how inputs and outputs (requests and responses) for geospatial processing services, such as polygon overlay. The standard also defines how a client can request the execution of a process, and how the output from the process is handled. It defines an interface that facilitates the publishing of geospatial processes and clients’ discovery of and binding to those processes. The data required by the WPS can be delivered across a network or they can be available at the server." (OGC Web Processing Service)

Petascope integrates with the 52°north WPS allowing to submit a WCPS request via WPS and deliver sets of coverages or scalars as results. The WCPS query can be in either XML or abstract syntax.

Deployment

First, the original war file from 52 north needs to be adapted for this to work. This can be done with make wps from the petascope directory. Note that the wps target in the Makefile needs to be adapted for this to work.

To integrate a newly deployed custom n52 war with petascope WCPS

  1. go to Upload Process and upload `petascope/src/main/resources/n52/ProcessCoverages.java and petascope/src/main/resources/n52/ProcessCoverages.xml
  2. Save configuration
  3. In Algorithm Repositories a property "Algorithm=petascope.wps.n52.ProcessCoverages" for the UploadedAlgorithmRepository needs to be added.
  4. Deactivate the LocalAlgorithmRepository

Internals

Incoming WPS Execute requests invoking the ProcessCoverages process are forwarded by the 52°north to petascope, stripped off the WPS specifics. The resulting WCPS request is processed, and the result is returned to WPS.

Technically, the coupling consists of an adapter class (a Process). The process identifier is petascope.wps.n52.ProcessCoverages.

Demo

See this small earthlook we have set a demo too, available EarthLook WPS demo. There is a simple test client done by n52.

WMS

"The OpenGIS Web Map Service Interface Standard (WMS) provides a simple HTTP interface for requesting geo-registered map images from one or more distributed geospatial databases. A WMS request defines the geographic layer(s) and area of interest to be processed. The response to the request is one or more geo-registered map images (returned as JPEG, PNG, etc) that can be displayed in a browser application. The interface also supports the ability to specify whether the returned images should be transparent so that layers from multiple servers can be combined or not."

Petascope supports WMS 1.0.0/1.1.0. How to publish a WMS layer.

Limitations

  • as the WCS CRS extension is not yet approved by OGC (although submitted by the WCS.SWG) CRS handling is still limited.

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