> I can't help but think that feeding data different constellations in all at once wouldn't produce a good result Obviously if you just mix up the bytes willy

> I can't help but think that feeding data different constellations in all at once wouldn't produce a good result Obviously if you just mix up the bytes willy nilly then nothing good will come out of it. How familiar are you with the terminology of mathematical optimisation? If you are then the intuition is that each satelite provides a different error term in one big function you are trying to optimise. The “knowns” you plug in to the terms are your observations (pseudorange, phase, etc) and the orbital parameters of the satelite broadcast by the satelites. The unknowns you are trying to solve are the x,y,z,t coordinates of the receiver you have. You are trying to find the unknowns which minimise the sum of the error terms. The error terms of the various constellations might have slightly different ”shapes”, but you can still run your optimisation them the same. As you add more satelite the number of unknowns remain the same (4), but you are adding more and more equations to your overdetermined system. When things are not pathological that leads to a better, more precise fit. > aren't they all doin the same thing Even if they were, sometimes it is valuable to have your own toy. If Russia is having a war in some region of the world and the US decides to turn off the GPS signals there is not much Russia can do about that. It is a US satelite and the US adjusts it as they see it fit. If Russia has their own satelites and the US would like to deny them this the US have to attack Russian assets directly. That is a very different ball game.