[mkgmap-dev] Multipolygon Role Understanding

Mon Feb 15 08:47:09 GMT 2021

Hi Jan,

I had a look at your troublesome multipolygon and in my view it should not
be a multipolygon at all. The inner roles in a multipolygon are 'cut outs'
best explained where a multipolygon is applied to a lake with an island
where the island is 'cut out' of the lake and has the role of inner, this
prevents it from being rendered under the water of the lake. The tags
relating to the lake are applied to the relation as a whole not the outer
way but the tags relating to the island i.e. name etc. are applied to the
way with the inner role. I presume that is why your workaround by changing
the outer role to an inner one works for the tagging in mkgmap. Another
example is perhaps an open area in a wood or open water in a wetland. In
your situation some components that are not part of the relation but are
obviously part of the water park render quite fine in OSM, technically the
parts of the relation with the role inner are not part of the water park
which in fact they are in this situation. A more suitable relation would be
site (https://wiki.openstreetmap.org/wiki/Relation:site) but even that does
not really apply here as the site is not dispersed over a wide area as a
college campus may be for example. As to how you find these errors I am not
sure, Geofabrik's OSM Inspector (http://tools.geofabrik.de/osmi/) can be
used to find many multipolygon errors but does not find this one, zoom to
the area you want to inspect and select "Areas" from the dropdown on the
left to show up tagging and role errors.

Just some thoughts.

Dave

-----Original Message-----
From: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> On Behalf Of Gerd
Petermann
Sent: 11 February 2021 10:00
To: Development list for mkgmap <mkgmap-dev at lists.mkgmap.org.uk>
Subject: Re: [mkgmap-dev] Multipolygon Role Understanding

Hi Jan,

the multipolygon processing happens before POI are generated.
With the original MP mkgmap creates a POI for the unnamed leisure of the MP
and probably also one for the outer way which (at this time) only has one
tag name="Naturfreibad Sankt Märgen". There is no rule for such an object in
the points file and therefore no POI is generated.

I also wondered how to detect this error. I expected that JOSM would
complain but it only shows an info message. Will look at this later.
No idea yet how to find those cases with overpass. You may search for a
specific tag like the leisure=water_park but I see no easy way to find all
MP where the MP repeats an important tag of one of the outer ways.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von jan
meisters <jan_m23 at gmx.net>
Gesendet: Donnerstag, 11. Februar 2021 00:15
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] Multipolygon Role Understanding

Hi Gerd,

yes, that works for me as described. As I understand, due to consecutive
processing: nameless leisure gone, next matched?
Another work_around I found by just changing the outer role to an inner.
Both indicates imho more likely a mistagging.

I´d like to have an overpass query to find similar examples - if anyone has
an idea: appreciated ;-)

Jan

> Am 10.02.2021 um 23:13 schrieb Gerd Petermann
<gpetermann_muenchen at hotmail.com>:
>
> Hi all,
>
> sorry, the style file is OK. I just tried with the (locally) corrected MP
(removed the leisure tag) and with that the name "Naturfreibad Sankt Märgen"
is shown in the map.
> I think the multipolygon code removes all tags from the outer way 
> which also appear in the MP. The remaining tags name=Naturfreibad 
> Sankt Märgen
> opening_hours=Jun-Sep: Mo-Su 09:00-18:00 wheelchair=limited are 
> ignored by the default style.
>
> The behaviour is intended, but in fact a bit confusing.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag 
> von Gerd Petermann <gpetermann_muenchen at hotmail.com>
> Gesendet: Mittwoch, 10. Februar 2021 23:03
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Multipolygon Role Understanding
>
> Hi Jan,
>
> I think the multipolygon describes the landuse, the outer way describes
the leisure. It makes no sense to have both tags on the MP.
> Reg. the missing "Naturfreibad Sankt Märgen":
> The default style doesn't use the name of the leisure, neither for the
polygon nor for the POI. Not sure why. I would have expected that inc/name
does that.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag 
> von jan meisters <jan_m23 at gmx.net>
> Gesendet: Mittwoch, 10. Februar 2021 21:11
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: [mkgmap-dev] Multipolygon Role Understanding
>
> Hi all,
>
> with my limited multipolygon knowledge I stumbled on missing poi tags
here:
> https://www.openstreetmap.org/relation/4077717
>
> The multipolygon is tagged more limited than the outer role.
> mkgmap renders the mp-tags, but drops the more useful outer tags (name
etc.).
> This useful it´s rendered on openstreetmap, but I can´t get it with
mkgmap.
> Tried default style and others, even OsmAnd (in OffRoad.jar) - all fail.
>
> So I wonder how or at all I could style the desired display in mkgmap.
> Of course the mp itself might be wrong - don`t know - but then I 
> suspect a lot of them ;-/
>
> Jan
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