A web processing service for GNSS realistic planning

The spread presence of Global Navigation Satellite Systems (GNSS) Permanent Station Networks makes satellite surveys simpler, quicker and cheaper and the achievement of high precisions easier. How- ever, the result of a GNSS campaign benefits from an accurate planning, especially in presence of natural or artificial obstructions that make satellite observations difficult. Most of the GNSS office suites provide plan- ning tools to analyse the satellite's visibility; visibility plots, sky plots and dilution of precision charts are commonly built from the GNSS almanac. They usually allow planning on single points, taking into account the obstructions due to terrain morphology or buildings by hand-drawing polar diagrams after a visit of each location to be surveyed. This task can be made fully automatic by using a digital surface model to build the obstruction plot and the almanac to evaluate satellites' positions, hence their visibility and not only availability, in a GIS. The procedure may be applied to whole areas to find the best time for the survey campaign. Taking a step further, this approach has been made available as a service by creating a Web Processing Service, which allows also non-GIS specialists to access this tool through a simple WebGIS interface. The user can select the satellites constellation, GPS or GPS and GLONASS, the cut-off elevation angle and the day, hour and temporal window of the survey. The service returns raster maps describing the minimum number of visible satellites and the maximum positioning dilu- tion of precision index in every pixel for the tempo- ral window. Moreover, the service implements some features of the UNAVCO Translation, Editing and Quality Check software, which can help to choose the location of new permanent stations. The implementa- tion follows the OGC specifications and relies fully on Free and Open Source Software, combining different systems to provide the user web interface, the data storage and the processing engine. The service features, the underlying technology, and some examples will be presented in this paper.