Thanks everyone for the replies. I have imported over 250 GPX traces from my running log, boy does that slow JOSM down. It seems Bing may be offset but having 100+ traces on some paths it is all just a big wide blob of grey. Still, the blob is offset. I might try and cobble together a tool to average them, in my non-existent spare time. Shouldn't be too hard for straight line paths (famous last words).
BJ - yep I would love to dive in, already have -- but would hate to spend hours editing only to later realise I need to painstakingly go through and fix everything I've already done! I am still curious to know what the positional accuracy of survey markers is meant to be, if anyone can enlighten. On Sat, Sep 1, 2012 at 10:47 AM, Ian Sergeant <ina...@gmail.com> wrote: > Agree with everything that Ben said. > > In addition, you may like to check the AGRI imagery. If the Bing and > AGRI imagery align exactly, chances are you have well aligned Bing > imagery. If the AGRI imagery aligns well with traces, it is easy > enough to shift the Bing background to align with AGRI, and go from > there. > > It may be an idea if you trace from bing offset, to mark that as your > source, i.e source=bing (offset). That way people coming after you > know what you've done. > > Ian. > > On 1 September 2012 09:53, Ben Johnson <tangarar...@gmail.com> wrote: > > Hi Russell, > > > > Welcome aboard. Just my thoughts... > > > > For a newbie, you've made some very astute observations about the > accuracy > > of the aerial imagery, so thanks for giving it the degree of thought - > > because many others just dive in and start tracing without understanding > > these subtleties. > > > > You're absolutely correct. Its quite normal for Bing (and others) to be > off > > by 10m or so, but in other areas it's very accurate. It differs all over > the > > place. > > > > Whatever editing tool you're using (Potlatch, JOSM, etc..), should give > you > > the ability to align your background imagery. Just be aware the further > you > > move away from the area you have aligned, the more likely the alignment > will > > need another adjustment. > > > > JOSM allows you "bookmark" such alignments. I have a bookmark for my home > > town. But the danger of bookmarking your aerial alignment is that if Bing > > updates their imagery, your bookmarked alignment will probably no longer > > apply. Just something to keep in mind. > > > > Your known survey mark is definitely an excellent start. You can make a > node > > in OSM to those exact coordinates, then align your background imagery so > the > > location of the survey mark in Bing aligns to your OSM node. > > > > I would not rely on other people's OSM edits on which to base your > > alignment. You don't know how accurate or inaccurate they are. Your > survey > > mark is the best way, and the GPS traces. > > > > Are you aware you can upload and share your GPS traces (in your profile > > section), and you can view all the uploaded traces while editing? This is > > great for aligning the background image. Depending where you live, you > might > > have some major roads in your area which already have lots of traces. If > so, > > that's great - try and find a couple of busy intersections to align and > you > > should get a good alignment. > > > > Otherwise you can try walking around a block several times, or around a > > park, or around a roundabout many many times (if you see men in white > coming > > to get you... Run!) Another method is to use a fixed point - and > approach it > > from different angles like cross hairs to a target. > > > > As far as GPX averaging goes, I'm personally not familiar with anything > that > > does this, but this list has some very talented people who can help or > point > > you in the right direction. I find software averaging is not necessary > > because if you look at the traces visually you'll immediately get a very > > good idea from their density when they're all presented together (eg if > you > > look at the traces on a busy dual carriageway motorway you'll very easily > > see an "average" for each carriageway). In built up areas you just need > to > > be mindful of whether traces originate from cyclists, motorists, or > > pedestrians... and apply a degree of commonsense. I'm not sure if > software > > can possibly distinguish between a set of traces from a roadway, and > another > > set of traces from an adjacent walkway / cycleway - in such cases an > average > > is meaningless. > > > > As far as tweaking other people's edits... if you're confident with your > > accuracy, I'd just do it. But if you want to take a more cautious > approach > > you can contact the original editor and ask whether they mind you > tweaking - > > or at least ask what method they used to position their nodes and let > them > > know you can make it more accurate for them. Keep in mind there are many > > "inactive" users who move onto other hobbies after a while - so if you > don't > > hear back from somebody after a reasonable time, consider it fair game to > > change it. > > > > Again, well done for going through this thought process, and welcome! > > > > BJ > > > > > > > > Sent from my iPhone > > > > On 01/09/2012, at 8:11, Russell Edwards <russell...@gmail.com> wrote: > > > > Hello -- brand new user here, please be patient :). > > > > I am trying to improve OSM in my home town. I notice that many/most OSM > ways > > are approx 5-10 m west of where Bing has them. > > > > Most either have nearmap or nothing as a source. There are no GPS tracks > to > > download. I could make some but they're usually in (random) error by > about > > the same amount anyway. > > > > I tried to check against the coordinates given for a survey mark in town, > > through http://services.land.vic.gov.au/maps/lassi.jsp (with conversion > to > > lat/lon with http://www.gracode.com/mapgrids.php ) ... this also had the > > Bing map out by about 10 m... but southward! > > > > Help! Three inconsistent systems - Bing, OSM and the survey mark. Which > if > > any should I trust at the 1-m level? > > > > Is there a tool for averaging GPS tracks? There are roads I have run > along > > dozens of times with a GPS track for every run. Maybe with averaging it > > could get to the 1m level of accuracy. > > > > (Yeah yeah, don't sweat the small stuff... I just can't stand seeing > streets > > running through people's front gardens...) > > > > Thanks in advance > > > > Russell > > > > _______________________________________________ > > Talk-au mailing list > > Talk-au@openstreetmap.org > > http://lists.openstreetmap.org/listinfo/talk-au > > > > > > _______________________________________________ > > Talk-au mailing list > > Talk-au@openstreetmap.org > > http://lists.openstreetmap.org/listinfo/talk-au > > >
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