> My Garmin eTrex HCx makes reasonable tracks under forest cover, > although the tracks are certainly worse under forest than under a > clear > sky. It's not the cheapest GPS unit you can get, but it's reasonably > priced and it's a great navigator to enjoy both OSM and commercial > maps > on foot or sitting in the passenger seat of a car. The ability to see > my own track has gotten me "unlost" more than once; it seems that > once > I've gotten into GPS mapping I've been more aggressive about going > into > unfamilliar and confusing terrain, so I've been getting lost more! >
compared to a SiRF III powered the eTrex is pretty lame in accuracy. but it uses less power and runs twice as long on a set of batteries > I think of track accuracy from a practical viewpoint. Having a > trail off by 20 meters isn't so important so long as I get the > topology > right. > +1, and only the rich guys with expensive tools will ever figure out how bad your track was. > I walked a segment of trail that followed a creek and always stayed > by > one side: when I looked at the tracks overlaid with Garmin's Topo > 2008, I saw the track crossing the creek. I was often within 10 > meters > of the creek, so this isn't 'crazy' If I'm loading this into OSM and > if the creek is there, I certainly feel pressured to manually push > the > trail across the creek so that the trail doesn't show false creek > crossings: that's an error that people when they're using the map and > could even cause confusion. > this is very important. consistency and relative positions wins over accuracy of a single point. traditional maps are always consistent but rarely accuract. > As for speed, it's an issue that GPS errors have a "brown noise" > characteristic: they look worse on longer timescales. If you're > standing at one place and your GPS seems to be swirling around in lazy > nested circles, it looks real bad. It's hard to average the > coordinates to get a betting point position. If you take a track or > go > walking for 4 miles or drive 40 miles in your car, that craziness is > still there, but it's made invisible by the scale of the map. > > > _______________________________________________ > talk mailing list > talk@openstreetmap.org > http://lists.openstreetmap.org/listinfo/talk _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk