[mkgmap-dev] Bug in Road Merging - actually doubling roads.

Fri Mar 30 12:04:09 BST 2018

Hi all,

when you use the default style you'll find a lot of duplicate arcs:
-  (multi-)polygons with highway=* & area=yes overlapping other highway=* ways
- if you use option --make-opposite-cycleways you'll see a lot of duplicated arcs for all the ways created by this option.
- errors where two OSM ways with highway=* and no area=yes share segments

Of course the duplicate arcs often have different routing attributes, e.g. type, road_class, road_speed, oneway, restrictions etc.
It seems that those duplicate arcs didn't cause problems so far, so I wonder in what situation we actually might want to avoid them?

So far I found only a few cases were I would not expect side effects, e.g.
1) https://www.openstreetmap.org/way/16584103 and https://www.openstreetmap.org/way/16584160
hw=service+area=yes overlaps hw=service
All attributes evaluated by mkgmap are equal, the duplicate arc is obsolete.
Possible action: Split one of the two ways, remove the duplicate segment(s).

2) https://www.openstreetmap.org/way/393299955 and https://www.openstreetmap.org/way/183285165
hw=residential+area=yes+name=* overlaps hw=residential+name=* + oneway=yes
The name is equal, the oneway attribute is not, other attributes are equal.
Possible action: Remove the duplicated segments from the area=yes way.
This would also be possible when the area=yes way doesn't have a name.
If only the area=yes way had a name we might add the name to the oneway before changing the area=yes way,
so that possible housenumbers are still found.

Things start to get complex when the style adds multiple lines for one or both OSM ways, also when one OSM way
overlaps multiple other OSM ways, e.g.  https://www.openstreetmap.org/way/393299955 also overlaps
https://www.openstreetmap.org/way/183212836 which has different attributes.

Maybe we can find rules to handle more complex cases later, for now I try to code these actions.
At least it should reduce img size.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Felix Hartmann <extremecarver at gmail.com>
Gesendet: Donnerstag, 29. März 2018 19:57:25
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] Bug in Road Merging - actually doubling roads.

Well up to 3 duplicates (plus original) way there is never a problem. 4 duplicates can be problematic, 5 duplicates IS in 90% of cases problematic. I think I will rewrite my style to have maximum two duplicates, but usually no more than 1. Any solution to get rid of duplicates completely if 5 or more would be nice - but it seems Gerd cannot find a solution so be it. And yes it's not always a bug is OSM data (especially with areas) - but mostly (95% of the cases I analyzed) it was.

On 29 March 2018 at 16:12, Andrzej Popowski <popej at poczta.onet.pl<mailto:popej at poczta.onet.pl>> wrote:
Hi Gerd,

I haven't followed this discussion, sorry if I repeat a case or problem is already dealt with.

When you use highways defined as area for routing, then area border is converted to road. Quite often there are multiple areas with common border. This common border can lead to duplicate reads. Data in OSM is correct and there is nothing to report, but it would be good if mkgmap could remove duplicate.

--
Best regards,
Andrzej

_______________________________________________
mkgmap-dev mailing list
mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk>
http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev

--
Felix Hartman - Openmtbmap.org & VeloMap.org
Schusterbergweg 32/8
6020 Innsbruck
Austria - Österreich