[OSM-dev] Mapnik output resolution

Dane Springmeyer blake at hailmail.net
Mon Feb 8 04:21:32 GMT 2010


On Feb 6, 2010, at 11:48 AM, Graham Jones wrote:

> Hi,
> My apologies - this is probably more of a Mapnik question than an  
> OSM one, but I am using the OSM stylesheet, so I hope someone knows  
> the answer!
>
> I am working on a little application to generate PDF map output with  
> points of interest highlighted (ie to produce a 'restaurant guide'  
> or 'tourist attractions guide' for an area) (http://www.townguide.webhop.net 
> ).
>
> If I select my map size to give 100 dpi resolution, the text size  
> looks ok, but the output is a bit fuzzy (because it is only  
> 100dpi).  If I increase the resolution to 300dpi by increasing the  
> number of pixels I tell mapnik to use the text size reduces (or  
> maybe it stays the same in pixels, but is smaller because I am  
> printing at higher resolution) and it is no easier to read - it  
> looks like mapnik uses a different zoom level because extra detail  
> appears that I do not really want.
> For examples please see http://www.townguide.webhop.net/output/73/townguide_poster.pdf 
>  and http://townguide.webhop.net/output/72/townguide_poster.pdf for  
> the 100 and 300 dpi versions respectively.
>
> Is there a way to tell mapnik what output resolution I want so that  
> the font sizes, road widths etc. come out correct at different  
> resolutions,

Coming soon (likely will land by the next minor release - Mapnik 0.8.0):

http://trac.mapnik.org/ticket/343

> or will I have to re-process the style sheet for different  
> resolutions?.

Yes, thats the recommended workaround for now. Holger (http://www.ancalime.de/ 
) had a ruby script to do this that might be useful.

> Any pointers would be appreciated please!

It would be great if you would attach sample images, with the bbox  
used to generate them, along with any comments to that ticket. Once it  
rises to a high enough priority to revise work on... the more examples  
for testing the better.

Dane

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