[OSM-dev] Mapnik rendering of mountain_pass = 'yes'

Stefan Wenk stefan.wenk at gmx.at
Sun Oct 5 15:38:56 BST 2008


Hi,

I'm trying to render mountain passes with mapnik. In the attachment you can 
find an example of the current status.
As everyone can see the result needs improvement, as the pass symbol does not 
follow the direction of the corresponding way (look at 
the "Scharnitzsattel"). 
What I did is that I just simply followed the general mapnik pattern for 
rendering of nodes.
 *) I took the mountain_pass.svg icon from 
http://svn.openstreetmap.org/applications/share/map-icons/svg/misc/landmark/
and generated *.png icons with svg-twotone
*) added the following two lines to the default.style of osm2pgsql:
 node,way   mountain_pass text
 node,way   ele          text
*) Enhanced the mapnik osm-template.xml - the patch is attached.

The problem is that according to the defintion the "mountain_pass" tag applies 
to nodes, not to ways. Therefore the rendering uses an icon. The icon would 
need to be rotated according to the direction of the way at the specific 
node, which is tagged with mountain_pass='yes'. There was some discussion if 
the mountain_pass tag should be a property of the highest node of the pass, 
or of the way. I believe that the method for tagging a mountain pass as a 
property of the highest node of the way is fine, but that the rendering way 
needs to be enhanced for it. By the way, the same applies to the bridge='yes' 
tag, if the bridge tag is assigned to a node and not to a way.

I think that one possiblity is to generate a short artificial overlapping 
dummy way in osm2pgsql. osm2pgsql could somehow create this dummy way, which 
consists of the very mountain_pass= 'yes' node plus one node, which lies on 
the way in a short distance, let's say in 25 meters. The "highway" tag of the 
dummy node could be set to the highway tag of the original way.
There are special cases if the node is an end-node of a way, and not somewhere 
in between. 
Another  possiblity would be to generate a tag for the node, which contains 
the direction of the way and select rotated mountain_pass icons in the 
osm.xml accordingly. I don't like this one.

Are there other possilities and what is the best method of addressing this 
issue?

thanks

Exosorange
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