GPS position

davewuk · 02-17-2005, 04:09 PM

So I have MapMonkey's thing doing it's stuff with GPS running. I see my position around 200 feet from actual and assume building reflections must be causing the error. If so, how is this compensated for when driving around built up city areas?

Laidback · 02-17-2005, 04:14 PM

Quote: Originally Posted by davewuk

So I have MapMonkey's thing doing it's stuff with GPS running. I see my position around 200 feet from actual and assume building reflections must be causing the error. If so, how is this compensated for when driving around built up city areas?

It's not! Search for 'dead reckoning'. I don't think it will be the reflections, more likely that you don't see enough sats.

Edit: Ah, just read your other post, 4 sats is only just enough, the clearer the gps' view of the sky the better.

wizawuza · 02-17-2005, 04:34 PM

yeah I consistently have at LEAST 7, usually 9 sats.. it's been within 10 ft, if not less.

Before I found the "optimal" location for the gps receiver in my car, i had times when it was 3 or 4 satellites...

man, 3 was sometimes off by 200 or so feet... 4 wasn't nearly that bad, but still, you may be barely holding onto that fourth one so it may as well be 3 sats.

Get a better position and more sats, and you should be fine.

Good luck

Laidback · 02-17-2005, 04:37 PM

Quote: Originally Posted by wizawuza

Get a better position and more sats, and you should be fine.

Good luck

See here for better positions - http://users.forthnet.gr/ath/nektar/kma/main.htm

davewuk · 02-17-2005, 05:30 PM

Laidback...

Thanks for replies, will have to hit a bit of open ground and see what happens. Surely cities like London & New York for example where most buildings are high rise, sat signals will be greatly reduced, won't this affect operation or is there still enough blue sky to gather sufficient info?

Laidback · 02-17-2005, 05:34 PM

Quote: Originally Posted by davewuk

Laidback...

Thanks for replies, will have to hit a bit of open ground and see what happens. Surely cities like London & New York for example where most buildings are high rise, sat signals will be greatly reduced, won't this affect operation or is there still enough blue sky to gather sufficient info?

No, it does affect it, greatly! So do tunnels & underground carparks! OEM sat/nav is linked to the odometer and probably a giroscope. So if there is no GPS signal but your odometer says your moving, then....