IMPLEMENTING A WPS SERVICE FOR AUTOMATIC FEATURE RECOGNITION IN ORTHOPHOTO MAPS
T. Kubik1, W. Paluszynski1, B. Kopanczyk1, A. Iwaniak2
1 - Wroclaw University of Technology; Institute of Computer Engineering, Control and Robotics; Wroclaw, Poland
2 - Agricultural University of Wroclaw; Institute of Geodesy and Geoinformatics; Wroclaw; Poland
The main idea of employing Web Processing Services (WPS) is to settle some intelligent image processing algorithms in a place that is reachable from the internet and provide them as OGC standards conforming WPS. In our earlier work we described an approach to feature recognition in orthophoto maps using feed-forward artificial neural networks trained as single class classifiers capable of recognizing different classes of land cover. This algorithm is now offered as a WPS service, possibly a part of a chain of processes, configured and triggered by service clients. Process chaining is a strategy used in GIS analysis, where the final objective is achieved as a result of a series of processing steps.
The WPS standard proposal (the last version published is 0.4.0) does not indicate any specific data required or output by the WPS. Instead, it describes a generic mechanism to describe data inputs required, and produced by a process. This data can be delivered across the network, or made available at the server, and can include image data formats. WPS specification describes three mandatory service operations: GetCapabilities, DecribeProcess and Execute, and additional features for process chaining, data pulling via URL-references and long-term transactions. The outputs from Execute operation can be directly returned to the client or else the server can store them as web accessible resources. In the latter case the Execute response is an XML document containing URLs for each stored output. Since process execution time might be long, the Execute response can include the process status information and a status URL. The client can use the status URL to inquire the server about the process status, and to obtain an updated Execute response. The final results are made available after process completion.
The current WPS specification is not very mature. The problems with implementing conforming services arises from the fact, that WPS does not treat well storage management, eg. it is not known what to do when a result is no longer needed, or when a result would no longer be available. There is also lack of formal WSDL and SOAP support.
A preliminary implementation of a WPS service described in this paper is written in C# language. Our goal is to make it available in the internet, along with a full-blown catalog service support, with open access to interested parties. More details are given in the paper, along with examples.