On Aug 31, 2010, at 8:27 AM, AJ Ashton wrote:
> 2010/8/31 Dražen Odobašić <[email protected]>:
>> On 31.08.2010 15:18, Iván Sánchez Ortega wrote:
>> Due to heavily corrupted dataset, polygons covering polygons which they
>> shouldn't, and it goes on for 15-20 layers of polygons. Resulting dataset is
>> visually correct, that is, resulting rasterized image is correct, because
>> polygons are stacked in predetermined order.
>>
>> Problem is i have a request that resulting mapnik raster should be
>> semitransparent, so it could be layered on top of other layers.
>
> I ran into this issue recently when I wanted to make a
> semi-transparent map with OSM's processed_p shapefile, which consists
> of overlapping tiled sections of polygons. Since I couldn't use a
> transparent symbolizer, I went with option 2. - designing the map
> without transparency, then running a small script to go over all the
> tiles after they had been pre-seeded and generating the transparency
> with ImageMagick. This isn't a great solution if you need to be
> rendering images on the fly, unfortunately.
In this particular case, and assuming that you've imported the coastlines into
a postgres table, you could also use the "!bbox!" feature of mapnik and the
st_union function in postgis to remove the overlaps for any given tile.
Generally I'd use some kind of post-process though. I'm playing with some of
those ideas in a tilestache composite provider, but it's still only half-baked:
http://tilestache.org/doc/TileStache.Goodies.Providers.Composite.html
-mike.
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michal migurski- [email protected]
415.558.1610
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