OpenStreetMap 開放街圖
I use a Garmin Edge 205 to record tracks from the various surveys that I have done. From trial and error I have learned that even small amounts of interference can reduce the ability of the gps to pinpoint its location. For instance, if its sitting by itself on the sidewalk it can generally zoom in to about +-4m. If its in my hand or I am looming over it, the accuracy drops to +-7m.
However, when the unit is sitting in my car on the passenger seat it can really struggle to accurately pinpoint itself.
Recently I tried mounting gps to the roof of my vehicle and have been rewarded with increased accuracy in my tracks. Tests out in the prairies (no large buildings, trees or stuff like it for miles and miles) have shown highly similar results for intentionally plotted routes. Bringing the GPS inside the car reduces the accuracy markedly.
That said, for most people without windshields that reflect satellite signals, the gps could probably be best placed on the dash.
That is all.
討論
由 liftarn 於 2010年03月 9日 12時36分 發表的評論
Perhaps you can try with an external antenna.
My GPS unit has a flip out antenna and in the car I usually get a 0.8 meter accuracy.
由 HannesHH 於 2010年03月 9日 12時55分 發表的評論
Also play around with the orientation of the device. I once read something about the etrex being most accurate when help upright, might have been a placebo, I am not sure. :-)
由 Pink Duck 於 2010年03月 9日 14時35分 發表的評論
I've long been pondering a way to get my GPS tracker above my head when walking for increased accuracy. It doesn't support an external antenna so the best I can achieve currently is holding it with an extended arm. I'd really like one of those Ordnance Survey GPS poles with sub-millimetre accuracy :)
由 lebsanbe 於 2010年03月 9日 16時39分 發表的評論
When my etrex Vista HCx is fixed on my bike I get the best results, so I guess the best position should be parallel to the surface.
由 robert 於 2010年03月 9日 23時41分 發表的評論
HannesHH: The etrex should be held _horizontal_. This is because it has a patch antenna, which has strong gain directed upwards around the edges. In this orientation, the high gain angles are pointed just above the horizon, which is the best for GPS reception. The same should go for any GPS that has a patch antenna (most bluetooth GPSs for instance).
liftarn: I think 0.8m accuracy is unrealistic for GPS. Your receiver's estimate is often very optimistic.
由 Baloo Uriza 於 2010年03月11日 11時01分 發表的評論
robert: Actually, 0.8 is perfectly reasonable under ideal conditions, particularly if the unit is also a WAAS receiver.