A Semantic Resolver for Coordinate Reference Systems

Abstract

Coordinate Reference Systems (CRSs) are at the heart of geo services. A large number of very different CRSs is in active use worldwide. EPSG maintains a well-known inventory of geodetic CRSs upon which most service implementations and also the standards of the Open Geospatial Consortium rely. For recent data and services, however, this set turns out insufficient - time series, climate and ocean data, etc. require time axes and non-spatio-temporal axes in addition. Further, when retrieving slices from geo data cubes, new, unforeseen CRSs need to be constructed on the fly, such as lat/t or lon/z CRSs.

To achieve a uniform handling of all CRSs we propose a URL-based identification scheme. This scheme naturally extends OGC’s EPSG identification URLs with parametrized CRSs and ad-hoc CRS and axis combination. Our approach currently is under discussion within OGC for adoption as a standard. We have implemented a CRS resolver based on this concept which accepts identification URLs and returns corresponding GML definitions. The resolver is available publicly to study and demonstrate feasibility of URL-based CRS naming schemes.

In this paper we summarize the concept and implementation of the resolver as a service following the described name type specification.