Can the GPS be so wrong?

What do you mean, “Massiv”?

GPS gets the positions of the GPS satellites and a time, no more!

The satellites have atomic clocks and send their time in very high resolution. The GPS receiver has no atomic clock.

So it is very difficult to measure how much difference in the times the satellites have sent. The relative distance between the satellites can then be calculated from the transit time. If you know the positions and relative distances, you can calculate your own position.

For this purpose, the GPS receiver’s watch must first synchronize to a satellite and calibrate its deviations. That’s why the first GPS fix takes so long. After all, the time differences of the individual data messages can be measured by different satellites.

If the clock has not synchronized correctly, the distances that are calculated are wrong. And as it comes to time measurements in the nanosecond range, you have a very big mistake. Then hundreds of kilometers can come together quickly, just if the receiver can only receive the minimum of 3 satellites. The more satellites are received, the more accurate the results can be detected and compensated for.

If you are in a building or between high buildings, it is very difficult to receive 3 satellites at all. And the reception of the data telegrams of the different satellites can take a lot of time and so the deviations of the clock in the GPS receiver are still much stronger.

For example, if you have a clock that goes wrong 10 seconds per hour, then every week half an hour goes wrong. After a year, they’ve been wrong for a whole day. And GPS is not a matter of seconds but nanoseconds!