[Talk-us] Separate relations for each direction of US & State highways.

[James Mast]

> From: lordsutch at gmail.com
> Date: Thu, 21 Nov 2013 03:27:21 -0500
> To: martijnv at telenav.com
> > CC: kristenk at telenav.com; talk-us at openstreetmap.org; hfyu at telenav.cn; vladimirl at telenav.com; chrisz at telenav.com
> Subject: Re: [Talk-us] Separate relations for each direction of US & State	highways.
> 
> The only problem I can anticipate with this tagging scheme is that it's possible some editors don't understand anything other than left/right/forward/backward (I think), we could end up in data loss situations fairly easily.

> > For example: way X pointing east is marked in relation Y as "east" (presumably we could assume that "east" = forward and the opposite cardinal direction "west" is backward). User reverses way X. Now the relation role is potentially backward.  JOSM seems to understand at least north/south and east/west and offers to fix it (see http://josm.openstreetmap.de/browser/josm/trunk/src/org/openstreetmap/josm/corrector/ReverseWayTagCorrector.java); no idea if iD or Potlatch do.

> > We'd also need to make the validation tools smarter to recognize lossage (for example, realizing that the route is unbroken only if the chain of role tags once you account for the directions of the underlying ways is monotonic),

> > > Chris> -- 
> Chris Lawrence <lordsutch at gmail.com>
> 
> Website: http://www.cnlawrence.com/

> 
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However Chris, there is a pretty big problem that JOSM has with cardinal directions, and it has to do with the relation analysis.  We need JOSM to be able to split the "lines" with cardinal roles when looking at a relation just like how it does it currently with the roles "forward/backward" [1].   That would be a major step forward it making sure relations have no gaps if/when we fully go cardinal from forward/backward.

If you want to see an example, download US-30's WV relation [2] into JOSM and change the cardinal roles all back to "forward".  You can then see the value of those splits in relation analysis inside of JOSM that the roles forward/backward have in making sure the relation has no gaps.

-James

[1] - https://josm.openstreetmap.de/ticket/5109#comment:18
[2] - http://www.openstreetmap.org/browse/relation/1593699
 		 	   		  
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