OpenStreetMap 開放街圖
I tried out the aGPS tracking with a Samsung Android phone yesterday in preparation for an excursion to the Montjuic cementary to record the labyrinthine street layout there, which would be most helpful to record how to get to specific monuments there. Unfortunately, the recorded track seem to have a large variety in the margin of error, probably depending on the correction available from the network at any given point in time. It look salright to record a few additional details in an area already heavily documented, but out in the field with a small number of large mobile cells it probably will be worse. I would not want to waste whole days meandering through the pathways only to discover afterwards that I got some sort of spaghetti artwork out of this… So… any recommendations on a sufficiently cheap but accurate GPS tracking device?
討論
由 robert 於 2012年08月11日 18時37分 發表的評論
I have a bt747a, available on ebay for ~£25. No display, but can hold ~100k trackpoints at once. And plenty accurate enough (though accuracy is always a problem in highly built up urban areas). MTK chipset.
There are several similar variants available on ebay.
由 Vincent de Phily 於 2012年08月13日 09時51分 發表的評論
Assisted GPS (aGPS) only helps to get the initial GPS position (“gps fix”) faster. It doesn’t improve accuracy, and having more mobile cells in the area doesn’t improve thins (as long as you have data coverage, you can use aGPS). Mobile phones generally don’t have great GPS quality, and narrow streets with high buildings are a challenge for any GPS.
I recommend one of the Garmin trekking GPS. The newest eTrex even support Glonass (an additional set of available satellites, which improves fix time and “deep valey” accuracy). They’re not as cheap as single-purpose trackers like the one Robert suggests, but you can view your osm maps on it, and they’ll last you a decade as they’re very sturdy. Some models even have a camera, but the price becomes hard to justify.
由 asgalon 於 2012年08月13日 13時10分 發表的評論
Ah, thanks for the info. I think I had some wrong ideas about how aGPS actually works. I thought it worked based on radio cell information and provided continuous information. I did a larger tour following one of the central streets from more or less in the middle of Barcelona to the beach and back again yesterday (osm.org/user/asgalon/traces/1291334) and the accuracy gets much better when away from higher buildings. What surprised me was that the trace while riding the bus back seems to have been as accurate as while walking.