[OSM-dev] t at h Lowzoom implemented :-) (nearly)

spaetz osm at sspaeth.de
Tue Aug 14 08:58:21 BST 2007


Crossposting, as that may interest more people that jsut tiles at home.

Using deelkar's holiday as he can't hit me with a stick now :-), I hacked away at the t at h client.

- I removed hardcoded assumptions that z12 is the lowest zoom level we ever use in the t at h client.
- I modified the t at h render client to fetch data from 80n's zappy API at low zoom levels.
- I added initial stylesheets that can be used on z6-z11

All that is in SVN now. As a consequence, we are able to directly render lowzoom tiles in osmarender with corresponding stylesheets (please don't use and upload with it yet, though). This implies all kind of potential goodness, like readable city names at low zoom levels, emphasized motorways and railways, County and Country names etc... Exciting, isn't it?

Of course this is still not mature, there are 2 areas which need improvement:
- Rather than mercator coordinates we use lat/lon. High low zooms this will skew things (I don't know by how much). Somebody will have to write a preprocessor to fix this. (not me)
- Sea tiles are not rendered as such. (neither are coastlines it seems). I have no clue about that sea lookup works during the render phase, so I can't promise a quick fix here. Deelkar, or Frederik might know that stuff better.

OK here are the pretty pictures :-):
I rendered z10 and z11 of the Dover/Calais area:
http://informationfreeway.org/?lat=51.21022180789198&lon=1.3561245842154883&zoom=10&layers=0000FB00

I am also currently rendering a z6 (up to z11) in the Zurich area as a test, which will be available here:
http://informationfreeway.org/?lat=47.277953754052376&lon=8.780134206689464&zoom=9&layers=0000FB00

(keep in mind that the low zoom stylesheets are not yet adapted to provide usefull sizes, so town names will still be tiny here...)

my next steps: 
-Develop stylesheets further to be useful.
-Look into sea tiles
-Make request queueing be smart enough to see if a low-zoom renderer or a high-zoom renderer asks for work and enable low zoom requests.
-Once mature enough, probably start rendering z10 and z11 directly and stitch lower zoom levels together from z10 for now.

spaetz
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