Re: accurate racetrack measurements with gps

From: Preben Mikael Bohn (nospam_at_nospam.com)
Date: 08/10/04 

Date: Tue, 10 Aug 2004 13:33:09 +0200

MatsB wrote:
> I assume kinematic refers to a moving unit, I am sorry that im unfamiliar
> with the terms, where would you draw the line between a static and moving
> unit? 3 minitues at the same spot or 3 hours? Since i am not measuring car
> movements but only the track layout I can spend some time at each point.

If you use simple software and cheap GPS units it can be done in 30 mins
(and probably down to 10 min as well) for each point for the ambiguity
resolution. If you are careful (read: no or only a few cycle slips), you
can even do a kinematic solution this way, thus only needing to _track_
all sats (while moving the antenna) for ~30 mins.

I think Carsten knows of a few "cheap" GPS modules that gives good
carrier phase output. I think they are typically around 200US$.

> Would it possible to use one gps as static reference, providing the errors
> at each time step.
> Then use another gps to move around the track.
> Then subtract the time-error vector from the time-measurement vector?

Basically this is differential GPS; if you need sub-meter accuracies you
need ambiguity resolution of the output carrier phases; if you know some
math and about programming you can do this yourself; otherwise you need
to use some kind of post-processing SW.

Another approach is to borrow the equipment (I have done this quite some
times).

Best regards Preben

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