Creating and viewing skyplots

Abstract.

One of the best tools for diagnosing problems encountered when processing GPS data is the skyplot, a simple illustration of GPS satellite trajectories over a given ground site. These plots, also called satellite visibility diagrams, provide an intuitive feel for satellite geometry and they reveal the impact of obstructions on satellite visibility. Most commercial GPS software is capable of creating skyplots; however, freely available skyplot software may be difficult to find. Thanks to freely available mapping software such as the Generic Mapping Tools (GMT) and postscript viewing software such as Ghostscript, GPS users can generate skyplots without concerning themselves with the intricacies of computer graphics or with printer drivers. Instead, skyplots can be generated by providing azimuth and elevation-angle input data which can then be converted into x, y coordinates for input into the existing mapping software. This article describes Windows-based C/C++ software for generating the azimuths and elevation angles, as well as software for viewing and printing the skyplots. All the software is freely available on the Internet.