[OSM-dev] PNG type for Mapnik map

[Tom Hughes]

In message <476910A2.6020706 at arjam.net>
        Robert Munro <rjmunro at arjam.net> wrote:

> Jochen Topf wrote:
>
>> http://svn.openstreetmap.org/applications/rendering/mapnik/generate_tiles.py
>> uses a call to the external 'convert' program to reduce the number of colors
>> for tiles rendered by Mapnik to 255. Since version r571 Mapnik supports
>> writing to 8 bit palette PNGs. Palette PNGs are generally smaller than
>> normal PNGs.
>> 
>> Is there any reason NOT to change the code to use Mapniks function to
>> write out the image directly as 8bit paletted PNG, make the images
>> smaller and save the call to 'convert'? (If nobody comes up with a
>> reason, I'll change the code.)
>
> AFAIK, the main reason the feature was added to mapnik was that /we/
> needed it because the external convert was really slow (about the same
> amount of time as the whole rest of the render).

The generate_tiles.py script is only an example - whilst changing it
is probably a good idea I don't think it will have an affect on
anything very much.

> So no, there is no reason not to change the code. Please do & make
> mapnik run at twice the speed. Also, if you can make mapnik render
> on-demand first, and only render the backlog when it's not busy, that
> would probably be a great improvement.

I think you're confusing mapnik the rendering library with the set of
tools used to render mapnik tiles for openstreetmap, most of which are
not in the repository as far as I know.

In particular any work along the lines you suggest would be best
directed at completing mod_tile rather than improving the current
ruby/python based code.

Note however that mod_tile already does most of the things you have
just suggested ;-)

Tom

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