[OSM-dev] How is the tile-index implemented/used?

Tom Hughes tom at compton.nu
Thu May 14 14:33:18 BST 2009


Daniel Gilbert wrote:
> Hi Tom,
> 
> thanks for your fast reply. ;)
> 
>> If you're trying to display planar maps then you will need to project 
>> them to the plane and you may want to do tiling post-projection, much 
>> as the slippy map tiles do, rather than on the original WGS84 lat/lon 
>> values like the API does. 
> I'm not sure if I got the point: instead of saving the lat/lon-values to 
> my db and calculate the coordinates on demand, I should rather convert 
> the values into a plane-projection like the slippy map does and then 
> create my tiles and search index based on it?

Well it's a design decision you will need to make.

The database we use for rendering mapnik tiles for example is held in 
the spherical mercator projection that we use for the map, because it 
means each object is only projected once when it is added to the 
database rather than being projected every time it has to be rendered.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/




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