I was sloppy in my wording.
I was trying to say ...
A single point in 3 dimensional space and time (obtained through measurement of transmission times from at least 4 satellites of GPS or one of the other GNSSs or obtained otherwise) is insufficient to define a line segment that is needed as the basis of navigation.
A point in space time, are we now time travelling as well? Giles fetch the Tardis
So you’re saying if given a single coordinate , a once off , and no update if you move, then you can’t navigate? Bit like if you were given a 5m x 5m square of map, with a red dot saying you are here, that did not update as you moved?
Clearly you can still navigate by what you can see. But you’re right, the single coordinate won’t necessarily help (much), on its own, just as the tiny fixed fragment of map won’t help you navigate.
But that’s a very long way from not being to able to navigate solely with a gps and your eyes.
If you think about it, you’ll also realise there are methods of navigation that are not point to point but based on terrain and / or valley systems. So not dependent on having a line segment as the basis.