With the basic version of the GSSE you can find out which periods of the year the sun passes above any given point on the skyline (for instance a tree top). You also get to know at what hour the sun passes that point (disregarding local daylight saving time).
The advanced version can give you a complete 360 degrees diagram of sun curves, skyline and hour of the day for any place in the world and any date, see screen shots for an example.
The professional version allows the user to store any number of diagrams, to upload them on the internet, and to take printouts - typically for use in selling real estate.
With the advanced and the professional version you can construct the skyline of a planned building and estimate its effects on the sun conditions on your terrace or another place of interest. You can use this documentation to influence unfavourable development plans.
How it works: You let the GPS note your location (latitude and longitude). You aim with your phone at points on the skyline and press the screen. The GSSE uses sensors in your phone to register the compass direction of each point and the angle at which you hold the phone compared to horizontal level. It compares these measurements of the skyline with data on the sun's height at your location at different dates and hours of the day. These data come from a mathematical model in the app. No internet connection is needed.