Identifying orthoimages in Web Map Services

Orthoimages are essential in many Web applications to facilitate the background context that helps to understand other georeferenced information. Catalogues and service registries of Spatial Data Infrastructures do not necessarily register all the services providing access to imagery data on the Web, and it is not easy to automatically identify whether the data offered by a Web service are directly imagery data or not. ork presents a method for an automatic detection of the orthoimage layers offered by Web Map Services. The method combines two types of heuristics. The first one consists in analysing the text in the capabilities document. The second type is content-based heuristics, which analyse the content offered by the Web Map Service layers. These heuristics gather and analyse the colour features of a sample collection of image fragments that represent the offered content. An experiment has been performed over a set of Web Map Service layers, which have been fetched from a repository of capabilities documents gathered from the Web. This has proven the efficiency of the method (precision of 87% and recall of 60%). This functionality has been offered as a Web Processing Service, and it has been integrated within the Virtual Spain project to provide a catalogue of orthoimages and build realistic 3D views.