Radio signal from GPS/GLONASS/Galileo/Beidou satellites is too weak to penetrate through walls. Thus, we can’t have regular GPS indoor.
Therefore, one needs to build an Indoor “GPS” – a local indoor positioning system:
Effectively, all acronyms above is the same thing, but with different names and slightly different meanings:
By the way, GNSS stands for Global Navigation. Satellite System. GPS, GLONASS, Galileo, Beidou are GNSS systems.
There are many different types of Indoor “GPS” possible. See a detailed review and comparison below:
Very quick advice on Indoor “GPS” technology and solution selection: