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Re: [Paparazzi-devel] Gps sensitivity problem


From: Hector Garcia de Marina
Subject: Re: [Paparazzi-devel] Gps sensitivity problem
Date: Thu, 16 Jun 2011 18:18:44 +0200

Hello Chris,

yeah, the GPS signal is heavily affected by the weather conditions.

In my experience in navigation, the absolute position is more affected than the relative position between two or more readings. So, if you can correct the first position with a well known source
(maybe a beacon, mark terrain with a map, etc), you can remove most of the GPS inaccuracy (this technique is typically also known as "pseudo-differential" GPS).

Be careful with the receiver configuration, there are a lot of GPS that "smooth" the position with many kind of filters, even extrapolating with you demand higher refreshment rates. Watch out with the GPS
velocity, many cheap receivers just interpolate between position to compute it, expensive ones calculate the velocity based on Doppler effect, or other algorithms.

In my opinion, the best signal is the raw signal, It has less latency and you can manipulate it knowing everything about the signal (phase, gain, etc). Checking out the xDOP signals is useful as well, as they 
notify you how accurate is your signal.

Cheers,
Hector




On Thu, Jun 16, 2011 at 3:39 PM, Chris <address@hidden> wrote:
I apologize for my previous message's subject
(gps problem), i was at work and i had many things on my mind.
I will try again in an open space but all other gps units i had could lock or at least receive something
at the same location where i tried this one, the only difference was the overcast weather
with rain clouds.
Maybe the gps receiver is affected by heavy clouds i don't know.
The gps unit is the GS407 from Sparkfun and it is brand new.
Just to be safe i ordered one of the Paparazzi designed GPS units from David as it looks to me
that quality control is lacking those days when it comes to mass produced units.
Thank you all for the help/suggestions.
Chris


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Héctor



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