Non-building:part parts of buildings are not rendered

[VladimirMorozov]

When a building has building:parts only those are rendered, but the outline which doesn't have a part is not included.
Compare churches here.

https://demo.f4map.com/#lat=59.4362195&lon=24.7407079&zoom=18&camera.theta=54.454&camera.phi=6.302
https://streets.gl/#59.43631,24.74125,35.75,356.25,713.98

Even if the building's height's is set, it's still not rendered if there are any parts
https://www.openstreetmap.org/way/301781529

[ivanbranco]

It's because of this Simple 3D Buildings rule (I found a more precise rule than the one I mentioned in #3):

When a building has any building:part=* areas, the building outline is not considered for 3D rendering.

[StrandedKitty]

This is a really deep problem.

AFAIK, F4 Map has a unique way of handling building=* areas that have building:part=yes areas intersecting them. F4Map's approach is to subtract all building parts from buildings and then render what's left. And if a building is fully covered with parts then it doesn't get rendered at all.

On the other hand, other renderers such as OSMBuildings, OSM2World, OSM go don't do this. They certainly don't follow this subtraction approach. I think all three of them have no distinction between buildings and building parts and always render everything, though I might be wrong.

When I initially did my research on how Simple 3D Buildings are supposed to work I haven't found that much information on F4 Maps approach of handling it. It seems like they've made it up and it doesn't follow the schema which is described on wiki.

As @ivanbranco pointed out, on Simple 3D Buildings wikipage it's clearly stated that buildings intersecting building parts should not be rendered. I've implemented exactly this, and it seems to work, building outlines do get discarded correctly. Funnily enough, the same wikipage states that F4 Map has full schema support, which it clearly does not (if we consider what's described on that page the schema).

But it seems like F4 Map's approach to handling outlines has had a strong impact on how people map 3D buildings, as it's the most popular renderer with such a wide Simple 3D Buildings schema support. So I wonder if the schema should be reviewed to reflect the way the most people actually map.

[Beakerboy]

As a second opinion, here’s how it is rendered in my project:

https://beakerboy.github.io/OSMBuilding/index.html?id=26889368&info

[Matthias84]

Yes I know the rule, but to be honest, most mappers and renderers handle it differently. They use building:parts to modify smaller blocks of the buildings on dedicated features, as this is the easiest way for little modifications and individualisation on buildings...

Here are some of many broken buildings in Rostock: https://streets.gl/#54.07926,12.14431,51.00,343.50,391.47

P.S: Anyway a pretty astonishing visual imprettation of S3DB and micrommapped areas 🤯 Thats what I hoped that renderings would look like, when we started the united tagging schema!

[Beakerboy]

There is also the following errors with the building data:

Way 713297322 is taller than building. (79.28>3)
Way 713297323 is taller than building. (79.28>3)
Way 713297324 is taller than building. (79.28>3)
Way 713297325 is taller than building. (79.28>3)
Way 713297326 is taller than building. (123.8>3)
Way 842822342 is taller than building. (34>3) 

[c-h-r-i-s-t-i-a-n]

I also do not like the subtraction approach. The mapper should be able to decide if the outline is rendered or not by adding building:part=yes to the outline. Unfortunately JOSM gives a warning in this case.

[ivanbranco]

Unfortunately JOSM gives a warning in this case.

Luckily I would say! As the Wiki says: "Note that building:part=* are optional areas used in addition to a building=* area."
It also makes sense logically, an element is either a building or part of a building, can't be both at the same time (that's why someone tags buildings with building:part=no, which is counter intuitive because adding it makes that element a building part...)

[sekerob]

This building renders complete to almost complete in StreetComplete, OSM Building and F4Map. It uses the type=building relation, has an outline and building parts with layering https://www.openstreetmap.org/relation/12485899. This was mapped > 2 years ago, well prior to knowing of existence of OSM Buildings and F4Map, only having removed the height=0 tag recently on the outline that suppressed it causing rendering max height for the whole building after which it turned it into a whole 1 height blob in SC, where OSMB and F4Map were correctly discarding the outline height tag / building outline already.

how it shows in StreetsGL, just the commercial ground floor.

JOSM gave no warnings at all when I removed the height from the relation outline.
https://www.openstreetmap.org/changeset/133405707

Hope this helps

[ivanbranco]

how it shows in StreetsGL, just the commercial ground floor.

because is the only building:part=yes, the other parts are mapped as building=yes with layers

[Beakerboy]

@sekerob

one problem is the members of the relation have the role “buildingpart” instead of just “part”.
https://wiki.openstreetmap.org/w/index.php?title=Relation:building&mobileaction=toggle_view_desktop

I suggest you look at the Burj Khalifa as a “gold standard” way to map building relations.

[StrandedKitty]

@sekerob

This building renders complete to almost complete in StreetComplete, OSM Building and F4Map. It uses the type=building relation, has an outline and building parts with layering https://www.openstreetmap.org/relation/12485899.

Parts in this relation have roles buildingpart, not part. I don't think this is valid tagging.

[ivanbranco]

@sekerob
Note also that the building name goes on the building=* outline, not on the type=building relation

This outline must be tagged with building=*. The outline also holds any other tags (e.g. address, name, overall height, operator, ...) which apply to the building as a whole.

[sekerob]

As simple as role/part tags standardizing, did some adjacent buildings while there that had no heights or levels and added some windows=no and colours, albeit the windows on the elevator shafts did not go away in this screen refresh. Looks much better now though. 👍

[sekerob]

@sekerob Note also that the building name goes on the building=* outline, not on the type=building relation

This outline must be tagged with building=*. The outline also holds any other tags (e.g. address, name, overall height, operator, ...) which apply to the building as a whole.

Actually it's not the name, just an easy reference placeholder for recognition in ID Editor while working with relations, for building at corner Avezzano-Bologna. It shows up in the relations list of the area. Renderers ignore these as intended.