Re: [OSM-talk] GPS Accuracy under Forest Canopy
2009/8/10 John Smith delta_foxt...@yahoo.com: I didn't record PDOP information and such, but are there any solutions to record decent GPS traces on trails under forest canopy data collection other than a high end professional GPS datalogger? Not all data loggers are the same some have a much higher sensitivity. +1, actually you don't need (for better accuracy than 100 m) a high end professional DGPS (at least several thousand quid). You might be able to use sat overlays to estimate the true path. won't be more precise though (if you really mean sat and not aerial photo). In the end you would be tracing from aerial and use the track just as an reminder. It really depends what options you have available and how much time, money, effort etc you are willing to spend on it. Yes, if you have some time it will be an option to wait for the leaves falling in autumn (seriously). cheers, Martin ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
--- On Mon, 10/8/09, Martin Koppenhoefer dieterdre...@gmail.com wrote: Yes, if you have some time it will be an option to wait for the leaves falling in autumn (seriously). What if they are evergreen and don't loose their leaves in autumn? :) ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
You might be able to use sat overlays to estimate the true path. won't be more precise though (if you really mean sat and not aerial photo). In the end you would be tracing from aerial and use the track just as an reminder. For this case, I checked with the Yahoo imagery, and the canopy totally obscures the trail. It really depends what options you have available and how much time, money, effort etc you are willing to spend on it. Yes, if you have some time it will be an option to wait for the leaves falling in autumn (seriously). That's good to know - for most trails in this areas, the canopy consists of leaves that will fall. I wasn't sure if that would improve things. Otherwise it'd be a shame not to be able to map the trails - the only trail maps currently are on paid trail sites or paper maps posted on information signboards. Thanks, Mike ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
I've done some rain-forest hiking, and I've noticed similar results. If you really want to see some wandering tracks, try hiking along the base of some cliffs, in dense forest. I have noticed that the errors do seems to be less the faster I'm moving. If I stand in one place for a while, the path can wander over quite an area if there is dense cover. If I walk fairly quickly, then it still has errors, but not as large. I think it must be finding more open patches and correcting itself more often. Stephen 2009/8/10 Mike N. nice...@att.net: I'm using netbook with just your average $30 GPS dongle to collect data. Today I took a 5 mile out-and back hike under dense forest canopy. The GPX traces for the same trail out and back are separated by as much as 100 meters. I didn't record PDOP information and such, but are there any solutions to record decent GPS traces on trails under forest canopy data collection other than a high end professional GPS datalogger? ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
-- From: Stephen Hope slh...@gmail.com I've done some rain-forest hiking, and I've noticed similar results. If you really want to see some wandering tracks, try hiking along the base of some cliffs, in dense forest. The area I was in was in a steep valley, and some areas are really wild. In the example http://home.att.net/~niceman/GPXTrace.jpg The upper left trace is mostly correct with the direction of travel shown. Point #1 I believe to be very accurate because it emerges in the correct corner of the parking lot. After I spent time in the parking lot and retraced, the error level jumps to the 100 meter range and stays there. It will be interesting to compare when the leaves fall. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
Stephen Hope wrote: I've done some rain-forest hiking, and I've noticed similar results. If you really want to see some wandering tracks, try hiking along the base of some cliffs, in dense forest. I have noticed that the errors do seems to be less the faster I'm moving. If I stand in one place for a while, the path can wander over quite an area if there is dense cover. If I walk fairly quickly, then it still has errors, but not as large. I think it must be finding more open patches and correcting itself more often. 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! 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. 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. 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
Re: [OSM-talk] GPS Accuracy under Forest Canopy
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
Re: [OSM-talk] GPS Accuracy under Forest Canopy
On Monday 10 August 2009, Apollinaris Schoell wrote: 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 You're thinking of an old eTrex. The new eTrexes (ones with an H in the name) have high sensitivity receivers, a sirfstar III or (usually) better. robert. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
Garmin calls it high sensitivity but thats marketing Maybe better than very old Garmin devices but much worse compared to a SiRF III I have a new Hcx and compared multiple times. Only 60, Oregon, Colorado use a SiRF III and they are much better in accuracy but drain batteries like crazy. Still like the Hcx because it's smaller and battery life is very important on long hikes. On Mon, Aug 10, 2009 at 12:01 PM, Robert Scott li...@humanleg.org.ukwrote: On Monday 10 August 2009, Apollinaris Schoell wrote: 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 You're thinking of an old eTrex. The new eTrexes (ones with an H in the name) have high sensitivity receivers, a sirfstar III or (usually) better. robert. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
On Mon, Aug 10, 2009 at 12:40 PM, Apollinaris Schoell ascho...@gmail.comwrote: Garmin calls it high sensitivity but thats marketing Maybe better than very old Garmin devices but much worse compared to a SiRF III I have a new Hcx and compared multiple times. Only 60, Oregon, Colorado use a SiRF III and they are much better in accuracy but drain batteries like crazy. Still like the Hcx because it's smaller and battery life is very important on long hikes. No, the 60Cx/60CSx are the only handheld Garmin models that have a Sirf Star III (well, maybe some niche units like the Astro or Rino have it). The Colorado has a MediaTek just like the Vista HCx. The Oregon has a STM Cartesio chipset, same as the Delorme PN-40. I haven't used a 60Cx or 60CSx model, but I had a Vista HCx and it performed quite well. There was a rough series of chipset firmware for the Vista HCx that had a problem with drifting from the true position under difficult conditions, but recent firmwares have fixed that (or you could use the old version...). It was definitely able to hold a signal under difficult conditions better than the PN-40 I have now. Karl ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
On Tue, 11 Aug 2009, Apollinaris Schoell wrote: 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 ok, so I'm in the rich guys list. I have an older etrex, the MSO has the newer etrex with the more accurate chip http://en.wikipedia.org/wiki/SiRFstar_III i also have a Neo Freerunner, which is more accurate with the Antaris 4 chip and we have been obtaining dataloggers with much newer chips and greater accuracy than any of those chips, where I have been able to see my trace down each side of the road distinctly on an outward and return journey These have been based on Mediatek MTK chips I have tried the photoMate i-887 inside a shopping cnetre building and think i can get enough traces to map inside that building, but not the carpark below. http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=67511 http://www.gpspassion.com/fr/articles.asp?id=175page=5 motto try to get the newest sort of chip to track places with very poor signal ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
On Mon, Aug 10, 2009 at 4:20 PM, Liz ed...@billiau.net wrote: On Tue, 11 Aug 2009, Apollinaris Schoell wrote: 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 ok, so I'm in the rich guys list. not yet, only if you have the professional devices with 10cm accuracy ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] GPS Accuracy under Forest Canopy
--- On Sun, 9/8/09, Mike N. nice...@att.net wrote: I didn't record PDOP information and such, but are there any solutions to record decent GPS traces on trails under forest canopy data collection other than a high end professional GPS datalogger? If a phone network and the phone supports it AGPS can help where GPS fails. Not all data loggers are the same some have a much higher sensitivity. You might be able to use sat overlays to estimate the true path. It really depends what options you have available and how much time, money, effort etc you are willing to spend on it. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
