[talk-au] Misaligned streets OSM or Bing wrong? - use survey mark?

Sat Sep 1 04:20:57 BST 2012

Russell,

Found this on a search. This might be your answer to average your tracks -

http://wiki.openstreetmap.org/wiki/Average_tracks

Sent from my iPhone

On 01/09/2012, at 11:35, Russell Edwards <russell2pi at gmail.com> wrote:

> 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 <inas66 at 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 <tangararama at 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 <russell2pi at 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
> >
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