Re: [Paparazzi-devel] GPS accuracy

[Dirk-Willem van Gulik]

On Fri, 30 May 2008, Haiyang Chao wrote:

> On Fri, May 30, 2008 at 8:38 PM, Mohammad Ali Haji Pour <address@hidden> wrote:

>       Yes, that is what I meant. Usually the last 4 decimal points of lat and 
> long that I
>       am getting from the GARMIN hand-held receiver is different from what I 
> get by
>       u-blox receiever.

> Did u check Pacc, Sacc, NumSV in messages or just GPS part in the GCS?
...
> NubSV stands for satellite numbers. Generally u must have more than 4 satellite 
> to get a good

This sounds fairly systematic - so one thing to check is the DATUM - are 
both receivers using WGS84 or, even better, the local DATUM ?

Also - do know that for some parts of the world (e.g. the Netherlands) - 
the geo-correction of google is incredibly poor - yielding 100's of meters 
delta's at sea level due to both datum-errors and conversion errors. (e.g. 
the WGS84 coordinate given for a pixel in the image is a) very far from 
the actual coordinate of that pixel projected onto the geoid used and b) 
very far from a WGS84 measurement with a proper GPS at that location 
relative to the datum.).

Thanks,

Dw.