[OSM-dev] osmarender: need help on fixing problems with rendering big lakes

Frederik Ramm frederik at remote.org
Tue May 8 10:13:07 BST 2007


> On the main map at informationfreeway.org the lake is rendered a
> little bit strange. The same problem occures at the Lake of Geneva
> [2].

Provided that you're talking tiles at home*:

Some of the broken lakes - those where the coastline is one single  
way - will probably be fixed magically once the tiles are re-rendered  
with API 0.4 (which will deliver the whole way to the renderer,  
unlike API 0.3 which delivered only a section of the way).

But in general, this is the "big area problem" that we've talked  
about in the past, and it will be solved as follows:

* expand close-areas.pl, which currently in its first version only  
supports coaslines, to support other types of areas like  
natural=wood, natural=water, landuse=...;
* if areas become so big that they completely encompass a level-12  
tile are (approx. 10km squared) and there is a danger of the renderer  
downloading a bounding box inside the area without catching any of  
its border segments, use "control nodes" distributed inside the large  
areas to tell close-areas.pl whether the tile is "inside" or "outside".

Since the close-areas.pl mechanism is quite new, we thought we'd  
first use it with coastlines for a while and start using it for other  
areas when it is stable. But if you're desperate to get the lakes  
right and speak Perl, feel free to have a go; close-areas.pl is in  
SVN (applications/rendering/tiles at home). You can read more about  
close-areas.pl here:



*) t at h mailing list is in the queue.

Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'

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