[OSM-talk] Strange GPS trace - drifting?

[Barry Crabtree]

Hi

Lars - yes the second & third roads from the bottom are supposed to be one
road, so I think at worst it is 100m-ish out.

The estate is on a perfectly level area, no forests etc. just buildings.
>From what you've all said I think it may have happened because I've just
changed from using a Garmin GPS that had an mounted antenna mounted on my
car roof, to a navi-gps that I was keeping on the front dash, so the
comments about having limited satellite view & this satellite passing effect
sound like what's been happening.

Nick - looks like I'll have to sort out some blu-tack :-) pity I can't fit
the old antenna on the new receiver...

Anyway I've been round again today & got some clean traces to upload.

Thanks all!

Baz.



On 10/31/06, Nick Hill <nick at nickhill.co.uk> wrote:
>
> I have noticed this occasionally to a few tens of feet. Yours seem
> extreme.
>
> Is the area on a northern slope of a hill? I ask this as the mis-alignment
> is
> mainly N-S. E-W alignment seems OK. Satellites high overhead on an
> east-west
> plane could give enough information for your GPS to track your longitude
> accurately, but not your latitude. Many satellites are on the southern
> horizon.
>
> Other important factors include how your GPS was mounted. If it is on a
> lanyard
> around your neck, it will at best ever see half the available satellites.
> Usually much less. Situation only a little better if on the dashboard of
> the
> car. When you turn a corner, a different set of satellites come into view,
> which
> your receiver will need to train on. Takes time, and in that time, your
> GPS can
> loose track where you are.
>
> If driving around, I mount it on the roof of my car with blu-tack and a
> back-up
> lanyard around the aerial. This way, it can nearly always maintain a fix
> on
> enough satellites to give reasonable accuracy. As you turn an obstructed
> corner,
> it is more likely to 'see' both new and old satellites for long enough to
> maintain a fix.
>
>
>
>
>
>
> Barry Crabtree wrote:
> > Hi
> >
> > I've been out mapping round a local residential area. Everything seemed
> > ok plenty of satellites in view, but when I look at the trace it seems
> > that over the space of a few minutes it has shifted what looks like
> > about 50/100 metres. I've put a screenshot of the trace at
> > http://wiki.openstreetmap.org/index.php/Image:Grangefarm-wierd.jpg but
> > haven't uploaded the gpx file because it doesn't look right!
> >
> > Any thoughts on what might have happened. I've been collecting traces
> > for a month & this is the first time I've seen anything like this. Have
> > I done something stupid?
> >
> > Cheers. Baz.
> >
> >
> > ------------------------------------------------------------------------
> >
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> > talk at openstreetmap.org
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>



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