Satellite data is frequently used for distance measurements, for example when runners inform themselves how far they have jogged using their own watches or smart phone apps. The transport industry also relies on so-called “GPS tracks”. Scientists in the field of geoinformatics at the University of Salzburg and Salzburg Research demonstrated in the scientific journal "International Journal of Geographical Information Science" that the distance between two positions with randomly distributed measurement errors is, on average, longer than the distance between two positions without any measurement errors.
"Positions are repeatedly determined by a GPS track in a specified temporal frequency. However, each individual position is not precisely at the place where it should be”, explained Peter Ranacher of the University of Salzburg, the author of the study. Although the measured distance is sometimes shorter and sometimes longer than the actual distance, the deviations do not offset each other.
This phenomenon involves a systematic error which depends on the specific device, reception, position of the satellites and conditions in the Earth’s atmosphere. The scientists demonstrated deviations of up to 15 percent in their tests. The newly developed formula is able to precisely calculate these errors.