OGC Web Processing Service and Table Joining Service: A land suitability rating system implementation case

摘要

In the geospatial domain, the Open Geospatial Consortium (OGC) has recently released two new web service interface specifications designed to enable spatial data provision, calculations and modeling on the Internet. These specifications are known as the Web Processing Service (WPS) and Table Joining Service (TJS). A WPS can be used to enable access to any sort of calculation or model, although it is primarily intended to operate on spatially referenced data. The data required by the service can be available locally, or delivered across a network. There is no limit on the complexity of model which can be delivered via WPS. WPS specifies a standardized way to make a model available as all three conventional types of web services, namely KVP GET, XML POST, and as SOAP. As such, it allows the client to choose their preferred method of implementation. WPS essentially defines a way to wrap a model so that it can be executed over a network. It has been implemented in JAVA, Python, and Ruby, and has recently started to become popular in the geospatial GRID computing community. TJS specifies an XML encoding of tabular polygon attribute data that is known as geolinkable data. This encoding includes a substantial amount of metadata that completely describes the data contents. The xml based geolinkable data format is thus useful as a way to store and exchange data suitable for polygon-based modeling. The Land Suitability Rating System for Canada (LSRS) assesses climate, landscape, and soil factors in order to rate the suitability of land for growing crops. Currently, the list of crops includes alfalfa, brome, canola, corn, soybeans, and spring-seeded small grains. LSRS has been under development since the mid 1980's, and implemented in a variety of desktop software. Recently, the model was rewritten and deployed as suite of web services, based in part on recent and emerging standards from the OGC. This paper will use the LSRS use case to demonstrate the utility of the WPS and- TJS and to describe the principles and generic approaches using OGC web services for computer network based modeling and modeling chaining.