# 3D-buildings on a 2D-surface or the world isn't flat everywhere

Hi,
I just began to map 3D according simple 3D Buildings.
But unfortunately I don’t live in a flat area and so we have houses like this here in the Black Forest in Germany:
http://pics2.mediastore.immowelt.de/A/F/1/A/43581FD7F66F4B6C8316B701447CA1FA.jpg
You see thre entrances on two different levels and two of them at ground-layer to tag with layer=0 and one of them with stairs to level 2 at this place. But level 2 is getting level 1 more left, where the “garage-entrance” is
And it might be possible, that there is one more intrance into the roof from leftside of the picture, which also begins at layer=0 there. This is typical for elder houses in our region of the Black Forest:
The problem is the flat 2D-surface of the “world” in OSM. So reality-mapping is impossible in these cases.
Any idea to solve problems like these?

I think you are German, so this talk of user:Tordanik will be very interesting to you:
http://wiki.openstreetmap.org/wiki/FOSSGIS_2013
His master thesis is about integrating DEM into O2W
http://wiki.openstreetmap.org/wiki/Research

Unfortunatly the SRTM modell isn’t that detailed (x,y,z resolution) that it would make sense in flat areas (as here in Mecklenburg Vorpommern), so we might need another VGI tools to add more details to the height levels. But AFAIK there are currently no further steps in http://opendem.info

Concerning the core of your question: We had this question in discussion when we created S3DB, but had no good (and easy) solution to that cases:
http://wiki.openstreetmap.org/wiki/Talk:Simple_3D_Buildings#Buildings_on_a_slope

Yes I am and we might know each other from the german forum
Thanks for your informations an links. I’ll look at them even if there’s no solution of that problem but maybe anytime in future we’ll get some.

In simple 3d is assumed that we start counting levels from lower-est building connection with ground level. So in your example garage will be at level 1 (assuming level 0 is ground level). But it will be look correctly only when we integrate ground height in 3d viewer

I live in such a building with different building levels being above or under the ground. My building looks odd, regardless which 3d viewer I take. But I know that resources are better invested to improve 99% of the buildings that have the same ground level all around.