Grundheim's Sun Exposure Simulator shows, for any address in Switzerland, where the sun stands at any time of day and on any day of the year, how much direct sunlight an apartment or house receives, and which shadows neighbouring buildings, trees and slopes cast. It is based on the real 3D building models from swisstopo (swissBUILDINGS3D), the terrain model (swissALTI3D) and the astronomically computed sun position. The shadow simulation runs in real time, nothing is estimated.
Two apartments on the same street can have completely different light conditions. A building to the south, a steep slope or a row of houses can rob a ground-floor apartment of almost all its direct sunlight in winter, while the top-floor apartment next door stays sunlit all day. Listing photos almost always capture the best moment – the simulator shows the whole day and the whole year, including the short, low-sun winter days when overshadowing is at its worst.
For the address you enter, the surrounding 3D buildings are loaded and placed on the real terrain. The position of the sun (elevation and azimuth) is determined astronomically for every time of day and every day of the year and added to the scene as directional light. The buildings then cast real shadows – onto the ground and onto each other. This lets you see straight away which façade gets sun in the morning, at midday and in the evening, and when neighbouring buildings cast shade.
The building and terrain data come from swisstopo's open geodata and cover the whole of Switzerland. The position of the sun is based on established astronomical formulas (SunCalc). The result is a very close approximation of real-world sun exposure; minor deviations arise from the resolution of the building models and from new buildings that may still be missing from the dataset. For a definitive assessment, visit the property at different times of day.