Re:No GPS required: our app can now locate underground trains
by bluGill on Wednesday November 13, 2024 @09:18AM
(#42126286)
The satellite also sends information about all the other satellites that a receiver should be able to see. This is what makes adding other transmitters hard/impossible I guess - no way to tell the overhead satellites that your ground station also exists (there would presumably be thousands of them - most not in range of your receiver which would be even more problems.)
Re:No GPS required: our app can now locate underground trains
by dietr1ch on Wednesday November 13, 2024 @12:10PM
(#42127896)
> I don't understand this. As far as I know, the satellite basically sends its identifier and precise time, and from this information (combined with the information in GPS calendar that tells the locations of the satellites) the recipient can determines its own location.
I'd assumed the GPS calendar was somehow broadcasted by the GPS network too.
> Were you proposing to assume the location of a 5m sphere the recipient is in?
I guess the proposal was to change the problem from pinpoint a single point in space, to figure out roughly where I am, in which case being anywhere in a tiny sphere is pretty much the same as being in a point after you account for errors.
How could it be possible to determine the location from a single timestamp and information about which satellite it belongs to? I suppose if the recipient already has a fix, then it could perhaps survive with less than 3 satellites by making some assumptions, but I imagine this will result in lower quality location information.
Were you proposing to assume the location of a 5m sphere the recipient is in?