does GPS give you elevation (z axis)?

[dpopiz]

does it tell you how high up you are with respect to some reference elevation?

 

[Brian23]

yes, but its somewhat inacurate unless you have at least 5 or more satalites.

 

[sharkeeper]

Yes it does.

I should be dead though as I have two out of three showing -118 feet and that's from damn near the highest point on the ship.

 

[Brian23]

If you get a high quality GPS they can be more accurate, but a typical one (around $300 retail) like mine is only accurate within +/- 100 feet with good reception.

 

[Mark R]

Yes, it does. As long as your receiver is able to pick up sufficient satellite signals for a 3D lock (minimum of 4 depending on satellite positions).

It will give you elevation relative to the map datum you have selected on your receiver (the default datum is mean sea level according to WGS84). WGS84 is not adjusted for 'real' mean sea level, or for irregularities in the shape of the earth. A local datum may be, but is only valid in the prescribed region.

GPS elevation is, however, very noisy, with deviations of 100-200 feet over the course of a few hours being relatively common. This can be significantly improved by equipping the receiver with a high performance atomic clock. More commonly, GPS elevation is combined with barometric measurments, with the barometric sensor providing indication of short term movements, and the GPS measurements providing a baseline calibration for the barometer.

 

[dpopiz]

hm..well I don't know if this changes anything, but for the application I'm thinking of (just some device I'm thinking up), the actual number doesn't matter -- I just need to be able to take the device to a specific location (possibly on a certain story of building) and "bookmark" that location and then have the device know the next time it comes to that location.

do you think that would be possible by any means (including barometers or whatever) fairly cheaply

 

[sharkeeper]

no!