During the last days, I attempted to document 3D features of some notable buildings from my region, mostly churches and castles.

Simple 3D Buildings and tagging consensus

Discovering what is the most used tagging scheme was a little bit confusing. At first glance, the OSM-4D roof table seemed to be promising as it offered some very useful tags for churches such as roof:shape=apse_gabled. Unfortunatly, after researching the topic, it appears that OSM-4D isn’t really supported at the moment. Consequently, I had to resort to simple 3D building.

Limitations

Apses and cone roofs

The simple 3D buildings however, while being “the best currently widely supported”, is quite limited. After asking how members of the community would tag apse_gabled and cone roofs, I resorted to divide the half domes of the apsed roofs into multiple small triangles with skillion roofs and document their direction angle. F4map seems so be able to render it in a satisfactory way at times and in some cases in a rather disappointing way. The roof:shape=pyramid was used instead of the cone tag. It seems to be understood by renderers. Of course, while one shouldn’t tag for the renderer, the feed-back of the renderers are useful to identify tagging mistakes.

Besides the cones and apses, having the possibility to tag roofs hipped on one side only would be quite convenient.

Equal min_height and height to create overhang roofs

In order to describe overhang roofs, I resorted to create a “building” with a min_height = to its height and then tag the roof. This element for instance was tagged this way:

building:part	yes
description	part 3 of the bell tower of the Epallinge church
height	12.75
min_height	12.75
roof:direction	118.64
roof:height	5.95
roof:material	tile
roof:shape	skillion

It seems logical but F4map doesn’t understand it at the moment. It might only be a matter of time, though.

Sources

In most cases, I used both the aerial imagery, personal knowledge (memory) of the buildings as well as freely available photogrammetry. but I will try to produce some photogrammetry to be more accurate in my next adventures in 3D.