Screenshot from the Display Geo Data App, showing Route 80 at the Great Salt Lake Desert near Salt Lake City (Bonneville Salt Flats, Utah) showing a distance of 48.7 km.

Measuring the radius of the earth from 3 selected vectors. Each small circle represents the endpoint of a vector from the center of the earth to the location of the GNSS receiver at the time the measurement was taken.

The points are measured using differential GPS to about 5 cm accuracy. The points were measured in earth centered earth fixed (ECEF) vectors in cartesian (x,y,z) coordinates by Multilateration of distances to multiple satellites in view at the same time, e.g. NAVSTAR and Galileo. The NAVSTAR satellites orbit the earth in an altitude of 20,200 km. So no measured distance to any satellite was less than 20,200 km.

So the received signals can not be emitted by transmitters on earth. No shape of the earth assumed, no refraction and no perspective involved. The App shows the vectors as they were measured. If the earth were flat, all points would lie on a plane with Z-Axis about 1287 m, the elevation of the Lake. But the corrdinates for a typical point are (−1,903,316.178, −4,451,650.518, 4,140,256.711) in meters. If you calculate the length of the vector l = √x² + y² + z² = 6,370,363.447 m, which is the distance of the point from the center of the earth or about the radius of the earth.