One of the oldest measuring technology is the sextant. A small device that measures the angle of the sun at noon, can predict the latitude of the earth. It is also possible to figure out the longitude and from there the exact location. In the past, using the stars enabled figuring out the location with great accuracy. However, stars are not visible in the day so it is very difficult to figure out the exact location in the day especially if the sun is behind the clouds. Once this works, this is effective to pinpoint a location of the measurement within 1 km.
Nowadays, we can use modern technology such as a camera and a database that can lookup database of stars and positions and can be used to determine exact location of the observer.
This enables the observer or the user to know the location using modern technology for the observation and the calculations. This enables the observer to be independent of GPS signals and find the location of the observer within a few meters.
This method has been patented (https://patents.google.com/patent/US9909866B2) and thus can be used by any person to calculate their position accurately when GPS signal has been jammed
