OT How does GMaps know elevation?

That?s because air pressure changes. Laser height measuring from satellites and planes for mapping works fine and is a lot more accurate than GPS.

GPS doesn't use lasers. The receiver triangulates signals from multiple satellites to determine x, y and z coordinates of the receiver.

The z coordinate (altitude) is not very accurate

Why is laser measuring much more accurate than GPS? They both use light and clocks. Eric

I know GPS doesn't use lasers. It uses radio waves which are light and move the same speed as lasers. What is it about using lasers that makes them more accurate? Eric

Because the laser is the most accurate way to measure things.

GPS doesn't. It used radio waves.

Yes.

It's a direct ping from the satellite or plane with the laser. With GPS its continuous radio waves with varying propagation effects. That's why you need more than one visible satellite with GPS.

A GPS receiver extrapolates from the satellite constellation. The closer to the horizon the birds are and the more angular distance separating them, the better it works. In cities or mountainous terrain the view of the sky can be limited so it has to work with those overhead. It has nothing to do with light unless you have an extremely loose definition of the spectrum.

With a laser you're bouncing the beam off an object.

Wavelength.

Mike.

Did your mummy say "Because I said so!" a lot?

Mike.

Nope, it's a laser pulse from the plane or satellite, travel time measured.

GPS is continuous transmission with digital encoding on that.

Mike Coon wrote

Nope, both mum and dad quickly worked out that doesn't work with me.

I still remember the mega stoush that happened when I refused to eat something like spinach. She never tried that again.