space fix

[bye bye]

Theoreticlly how high of the ground can you get a fix with a gpsr? Do the satellites give a fix behond there altitude?

[+Renegade Knight]

Good question.

 

The answer depends on the math inside the GPS.

 

The satalities can only give out one type of signal. That signal would be just as valid above as below.

 

However if the GPS "Assumes" you are on earth they would probably give you garbage for readings once you are above the limites of use assumed by the GPS in how it intreprets the information coming from the satalites. This is probably the case but it's only my SWAG.

 

=====================

Wherever you go there you are.

[+Team GPSaxophone]

This is similar to the Y2K bug. You won't know until you're actually beyond the GPS satellite orbit (11,500 miles or so).

My guess is that the satellites only point their transmitter down towards the Earth. Once you acheive an altitude that's high enough, you will be in a dead spot where you don't receive enough of a signal.

If you happen to be directly under one satellite, you can go as high as that 11,500 miles, but only that one satellite will show up on your GPSr. You won't get position data, but should still get time and date.

If you are an equal distance from 3 satallites (triangulation, anyone?) then you will lose signal at a much lower altitude. I won't go into the trigonometry that it would take to determine that altitude here, but you couldn't achieve that altitude in an airplane anyway.

 

Took sun from sky, left world in eternal darkness

[+parkrrrr]

Unrelated to the theoretical exercise, I know, but most (all?) consumer-grade GPS receivers are designed to stop reporting fixes if they are above a certain altitude or traveling in excess of a certain velocity. This makes it a lot harder for backyard rocket enthusiasts to build their own eTrex-guided ICBMs.

 

[+Team GPSaxophone]

Although I was still well short of the sound barrier, my Etrex Venture recorded a max speed of 648 MPH on a flight from Albuquerque to Dulles.

 

Took sun from sky, left world in eternal darkness

[Kerry.]

GPS is designed to provide positions "on or near the earth"

 

"Near the earth" in GPS terms is low earth orbit vehicles like the space shuttle, which uses GPS. However there's no commercially available GPS that has this capability but they are made.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Team GeoCan]

The three or more signals recieved from the GPS system Satellites are computed on the bearing and the signal strength.

 

The satellites are in a known position, ("Fixed" in the equation, although they are moving)

 

The distance from the origin point is calculated. on EACH satellite in range.

 

YOUR point should be where the spheres of "signal" intercept in space.

 

There can only be one legitimate interception point if the math is right.

 

If a signal is lost, it is deleted from the equation.

 

The more signals the closer the accuracy should be. There s a "fudge factor" built into the math to allow near matches in position to be "averaged" which makes the whole thing work. if the positions do not converge mathmatically, becuse of some unlknown factor, the unit would not display a result until they did, but if within a set percentage or distance all results came out the display is designed to select the tightest group, and average it

 

Jeff Scism, IBSSG http://blacksheep.rootsweb.com/

 

Is it more important to know what you are talking about,

or more important to talk about what you know?

 

the seeking is in the knowing

and not where you've been

Travelling is the going

isn't learning Keen

[Kerry.]

The GPS Standard Positioning Service volume specifications goes out to 3,000 kilometres.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go