[Tagging] Simplify building:part areas

Marco Boeringa marco at boeringa.demon.nl
Fri Aug 18 10:03:22 UTC 2017

With building:part you are actually describing 3D volumes. These volumes 
don't necessarily start at ground level, but ideally should not 
intersect in 3D. As you can see in the Simple 3D building specification, 
you can set a "building:min_level" and "min_height" to "raise" a certain 
part from ground level to its appropriate starting height. So in your 
case of a large single story ground level part, and a smaller top 
section, you could set building:min_level and min_height tags on the 
part for the smaller section to raise it above the large section/part, 
which in that case should NOT  be a multipolygon.

Of course, like you suggested, there is the alternative solution of 
creating a multipolygon and setting the higher part to start at ground 
level as well by not specifying building:min_level and min_height, and 
that would be correct too in terms of non-intersecting 3D volumes, but 
the first solution without multipolygon seems more logical in this case 
(unless the higher part was in reality a true separate section starting 
at a ground level, e.g. office, within a larger structure, in which case 
it might make sense to use the MP option if you would like to tag 
function on the building:part as well).


Op 18-8-2017 om 10:36 schreef Javier Sánchez Portero:
> Sorry, I should have taken time to give some examples. Please read 
> below (I rev.
> 2017-08-18 1:30 GMT+01:00 Clifford Snow <clifford at snowandsnow.us 
> <mailto:clifford at snowandsnow.us>>:
>     On Thu, Aug 17, 2017 at 4:12 PM, Javier Sánchez Portero
>     <javiersanp at gmail.com <mailto:javiersanp at gmail.com>> wrote:
>         I am thinking in ways to reduce the complexity that introduces
>         the mapping of parts of buildings. For example:
> I have reversed the order of the points
>         * In the wiki [1] says that the outline should be tagged with
>         building:levels and height, but this, if the parts cover the
>         whole outline, is a duplication since these tags will always
>         be in some of the parts. Could I delete the part(s) whose
>         labels match those of the outline?
>     If you use a multipolygon, then the multipolygon would contain the
>     levels and height.
> I'm refering to 3D modeling of building height and levels, according 
> to [1]. For example, this building [2] have two heights and should be 
> drawn two parts inside the building footprint, one with 
> (building:part=yes, building:levels=1, height=3) [3], and another one 
> with (building:part=yes, building:levels=2, height=6). As the building 
> footprint [2] could have the levels and height tags I put them in it 
> avoiding to draw one part. I meant, the building area is not entirely 
> covered by building:part areas. All the building in this village was 
> drawn according to this.
> I take the rule to put in the building:levels and height tags of the 
> full building those of the level wich parts sum a greatest area 
> instead of the maximum values. For a example see the adjacent building 
> to the left [4]. It have (building:levels=1, height=3) instead of the 
> maximum values (building:levels=2, height=6) of the building:part [5]. 
> This way I avoid to draw two parts inside the building. I consider 
> that the maximum building:levels and height could be calculated by a 
> consumer from the building and its parts instead. I'm wrong with it? 
> But it's against what says the wiki [6].
>         * If one part is inscribed within a larger one, can I use
>         simple ways overlapped and leave to the render decide how to
>         draw them or should I create a multipolygon for the larger
>         part with the smaller part with inner role? I'm prone to the
>         first.
>     An example would help. If the building has an inner court yard,
>     then a multipolygon would be appropriate, with the inner court
>     yard with an inner role.
> I'm not referring to buildings with holes but to nested building:part 
> areas. Consider this building [7] with a big one-story part and a 
> smaller two-story part [8] within it. If I use the full detailled 
> schema I will need a multipolygon relation for the one-story part, but 
> I avoid this putting the tags in the footprint (violating the rule of 
> maximum levels and height in it). I don't have real example at hand, 
> but supposes another three-story part inscribed inside the two-story 
> part [8]. should I use a multipolygon for the two-story part to fully 
> separate it area from the three-story part area? Or could I just draw 
> the inner three-story part, overlapping both areas?
> [1] https://wiki.openstreetmap.org/wiki/Simple_3D_buildings
> [2] http://www.openstreetmap.org/way/459549932
> [3] http://www.openstreetmap.org/way/459550128
> [4] http://www.openstreetmap.org/way/459549958
> [5] http://www.openstreetmap.org/way/459550129
> [6] https://wiki.openstreetmap.org/wiki/Key:building:part
> [7] http://www.openstreetmap.org/way/215569626
> [8] http://www.openstreetmap.org/way/459573978
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