Re: estimating error in my GPS position.

utilsea@xxxxxxxxx wrote:
Hi,
first of all, using GPS velocity mesurement is not suitable at all for
that kind of observations.
You will record accelarations generated by the wave and other
movements of the buoy and I think it's not what your are looking for.
Today, a standart GPS is offering an accuracy within 15 meters in the
worst case who means 30 meters between two consecutive measurements.
You can improve this accuracy by using SBAS if you are under SBAS
coverage (WAAS, EGNOS, MSAS ...) to 3 meters (6 meters total error
between two points).
I think that you want also know the course of that drift derivated
from two position.

The only one way I see to solve this, is to increase the observation
time to get the global positionning error smaller as possible in
comparison of what you want to
detect.
Maximum GPS error is a "constant" and after 1 sec, two years or more
still the same. The only one parameters on wich you can play is the
observation duration.
Finally this means that if you want an accuracy of your measurement
better than 0.01 m/s in the worst case you have to make an observation
or take a sample every 3000 seconds (Observation interval = GPS total
error / requested accuracy) who can be decreased by the use SBAS
corrections.
For the course it's the same think but with the covered distance that
time (course accuracy = asin(GPS error / covered distance))

Eg : with a drift of 1 knots (0.5 m/s) and observation interval of
3000 s you will get an accuracy of about 1° using single GPS and 0.2°
using SBAS receiver.

Hope this will help you.

Cheers

Utilsea
http://utilsea.free.fr




The OP did not ask, but I would have thought it would be fairly useful to know for example the vertical velocity caused by the swell. You could get that from the vertical GPS velocity, but certainly not from the vertical position ( altitude ) data.

Sure if you want long term drift distance and direction, you need the position data, but for short term measurements, the velocity direct from the GPS will give you much better accuracy.

--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.
.

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