[OSM-newbies] Road below a building

[Randy]

Lennard wrote:

What is
>harder in mapnik, without explicit tagging, is determining when exactly
>a road is under a building, and making a clean transition from normal
>rendering to 'sheltered' rendering.

I would tend to leave that to the mapper, as long as the renderer can 
determine that the road does in fact intersect a building (or other 
object). The mapper should break the way at the building edges (or 
slightly outside, to avoid any computational problems),  so that the 
renderer only has to take care of that segment. If more road is rendered 
as under something than should be, the mapper should be the one to fix it, 
in my opinion. It's only slightly different from a bridge. The mapper has 
to denote the extremities of the bridge. Granted one is explicit and the 
other is implied, but if you draw a road under another object, or add a 
building on top of a road, you as the mapper should be responsible for 
establishing the ends of the covered road.

I've been considering this from a more global perspective, and, as a 
matter of fact, it might be a workable solution all around to just add a 
highway tag, "covered=yes", which would always be rendered as broken lines 
and transparent fill. That would be real easy for the renderer, and give 
the mapper explicit control. This would even work for another case I am 
aware of where the building has a small ground floor, with one shop, a 
stairway and an elevator. The upper floor extends over a parking 
area/service road. It's really not appropriate to break the building into 
two pieces, since the second floor is contiguous.

I can think of other cases that it would resolve as well. How about a road 
that has been covered by a lake. It may be nice to have the submerged road 
marked to give anglers a general idea of where to fish (often along the 
shoulders of the road, especially if the road is either raised or lowered 
from the surrounding terrain)>

-- 
Randy