[Routing] Errors in map data that affect correct routing - and what to do about it...

GS gerhardschwanz at yahoo.de
Mon Jan 5 07:18:16 GMT 2009


Hi Cathy,

once I've been to Edinburgh, came by ferry and car to explore the northern coast of Scotland. That was a nice time. Now I have a wife, a house and a child leaving not much possibility for such travel. But luckily I can do other things :-)

I think I can help you a bit. 1st I think that these double nodes are errors. Done by whatever version of whatever program. I think you can not prevent all errors. I think the API should reject those ways. However, now they are there. JOSM now has a good validator plugin. But it's a plugin, has to be installed deliberately and has not been there all the time.

I will write a check program for these which we can use to identify those ways. Not a big deal. Should be done today or tomorrow. But then they will only be identified, not corrected.

I just know about problems in routing, I don't actually "route" myself. I am the "checker". :-)

One other thing. I think the OSM data/graph should be simplified to save ressources when routing. I could imagine a simplifier eliminating those nodes and those that are not the end of a road and don't connect to anything else. Of course the weight/length of the original path should be maintained.

Cheers

Gerhard
gary68



--- Scott, Cathy <C.Scott at napier.ac.uk> schrieb am So, 4.1.2009:

> Von: Scott, Cathy <C.Scott at napier.ac.uk>
> Betreff: [Routing] Errors in map data that affect correct routing - and what to do about it...
> An: "routing at openstreetmap.org" <routing at openstreetmap.org>
> Datum: Sonntag, 4. Januar 2009, 22:56
> Gerhard,
> Thank you for posting this . I'm just away to look at
> it.
> I am studying for a PhD that is based on routing
> algorithms. At present I have a MYSQL copy of the
> Openstreetmap data for Edinburgh that I am using for this. 
> I certainly have issues  with the accuracy of this data that
> is
> causing issues with routing. Ways that are not connected to
> an others are certainly an issue. I was just about to come
> onto the forum to post about it when I saw your post...
> 
> One of the other issues that I have are Ways that appear to
> have extra nodes on them that I do not understand why they
> are there. I'm assuming that they are errors but I
> wanted to double check first...
> 
> For example there is a road called Charles Street in
> Edinburgh way id =7972092. This way has 4 distinct nodes but
> the last one is repeated so that a routing algorithm moving
> along the street would move from node id= 287241490 to node
> id=287241490. 
> I'm assuming that the above example is an error. There
> seems to be plenty of them too. In the Edinburgh area I have
> identified about 100. Some of them are completely
> unnecessary Ways. For example Blacket Place is represented
> by two ways. the first id=27992340 appears to be valid. The
> other way id=4048677 consists of one node(id=307349548) 12
> times!
> 
> Of course I could code any routing algorithm to ignore
> these 'null' moves but I was wondering;-
> a) How do these errors get there? Can validation checks be
> added when ways are created/updated?
> 
> b) Have you found an issue with these errors or are you
> just coding to ignore them?
> 
> Thanks,
> Cathy
> ________________________________________
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> routing-request at openstreetmap.org
> [routing-request at openstreetmap.org]
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> To: routing at openstreetmap.org
> Subject: Routing Digest, Vol 16, Issue 9
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>    1. Errors in map data that affect correct routing - and
> what to
>       do about it... (GS)
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> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Wed, 31 Dec 2008 10:10:51 +0000 (GMT)
> From: GS <gerhardschwanz at yahoo.de>
> Subject: [Routing] Errors in map data that affect correct
> routing -
>         and what        to do about it...
> To: routing at openstreetmap.org
> Message-ID:
> <415114.94194.qm at web25501.mail.ukl.yahoo.com>
> Content-Type: text/plain; charset=utf-8
> 
> hi,
> 
> from time to time people encounter errors in routes or
> destinations can't be reached. there are a lot of
> reasons for this. and a lot of reasons can be found in the
> output of my check programs.
> 
> so if you no longer want to do "trial and error"
> and want to correct the map data proactively have a look at
> the programs and their outputs.
> 
> waycheck looks for unconnected endpoints of ways and
> crossings of ways on the same layer where the ways don't
> share a common node.
> http://wiki.openstreetmap.org/wiki/WayCheck
> 
> checkconn does the above mentioned check, but faster and
> with less memory.
> 
> checkcross does the above mentioned check, but faster and
> with less memory.
> 
> checktouch checks for endpoints of ways that nearly touch
> another way. so presumably these ways should be connected.
> 
> motorwaycheck checks for invalid motorways (invalid oneway
> tags and possibly wrong directions of ways).
> http://wiki.openstreetmap.org/wiki/MotorwayCheck
> 
> lots of reports can be found here:
> http://wiki.openstreetmap.org/wiki/DE:WayCheck
> 
> all programs can also be found on my wiki page:
> http://wiki.openstreetmap.org/wiki/User:Gary68
> 
> generally there is a wiki page for quality assurance here:
> http://wiki.openstreetmap.org/wiki/Quality_Assurance
> 
> 
> cheers
> 
> gary68
> gerhard
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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