[OSM-talk] buildings

Iván Sánchez Ortega ivansanchez at escomposlinux.org
Tue Jul 24 22:15:10 BST 2007


El Martes, 24 de Julio de 2007, Steve Coast escribió:
> So, my question is what's the status of building=* and what is the
> status of mapnik and t at h rendering it?

AFAIK, mapnik doesn't render buildings, but t at h does.

> If those two or three things line up, should we start putting in the
> outlines of lots of buildings?

We (spanish guys) have already put a number of *important* buildings: 
monuments (castles), administrative (courthouses), or otherwise important 
(stadium annexes).


I suggest to delay *massive* building tagging (i.e. every building possible) 
until we have a way to accomodate cadastrial data *and* touching, ordered 
ways.

For the first point, put this into your .josm/preferences file, get any area 
of urban spanish soil, zoom in a great deal, and get an image:

wmsplugin.url.7.name=Spain cadastrial data
wmsplugin.url.7.url=http://ovc.catastro.meh.es/Cartografia/WMS/ServidorWMS.aspx??SERVICE=WMS&VERSION=1.1.0&REQUEST=GetMap&SRS=EPSG:4326&LAYERS=Cartografia&STYLES=&FORMAT=image/png&

You'll see how many *stories* (and balconies, and underground floors) every 
building has. How can we deal with that kind of data?


The second problem is more grave IMHO: according to the actual standards, 
there is no way to correctly *draw* three touching (adjacent) ways.

I'll explain myself: the current data model (and validator rules) encourage 
the following:

- Reuse data (reuse a node if possible)
- Reuse a segment if you really, really need to
- Closed ways "areas" must be ordered. Either it draws a clockwise polygon, or 
a counter-clockwise polygon.


When drawing buildings, we "really really" need to share segments between 
ways: those buildings are touching, indeed.

Now, with that in mind, it's impossible to draw three adjacent areas, 
maintaining "clockwiseness" in evert one.

Warning: crappy ascii-art follows. Switch to a fixed-width font:

+---------------+
|               |
|               |
+--------+------+
|        |      |
|        |      |
+--------+------+




Gentlemen, start your flamethrowers...

-- 
----------------------------------
Iván Sánchez Ortega <ivansanchez at escomposlinux.org>

"You can get more with a kind word and a gun than you can with a kind word 
alone."
 - Al Capone (1899-1947)
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