I've added a page to the trac wiki around this topic http://trac.mapnik.org/wiki/ScaleAndPpi
Please consider it a first draft! ---- Jay ----- Original Message ----- From: "Dane Springmeyer" <[EMAIL PROTECTED]> To: "Christopher Schmidt" <[EMAIL PROTECTED]> Cc: "Mapnik users mailing-list" <[email protected]> Sent: Friday, November 21, 2008 9:21:56 AM GMT -08:00 US/Canada Pacific Subject: Re: [Mapnik-users] 300 dpi images with Mapnik? Chris, Big thanks for the clarification. I'll take a closer look at the code with your description in mind. Dane On Nov 21, 2008, at 4:00 AM, Christopher Schmidt wrote: > On Thu, Nov 20, 2008 at 10:52:24PM -0800, Dane Springmeyer wrote: >> Isn't DPI just a printing/ink term? I don't think Mapnik's map scale >> is DPI dependent. > > Scale is "map units per unit on paper" -- so, 1:24000 is "one inch in > the map is 24,000 inches on the ground", etc. > > This definition of scale requires you to have some idea of how big > "one > inch" is in pixels -- which is where DPI calculations come into play. > If you are printing at 300 dots per inch, then a 300 pixel wide > image is > giong to be one inch wide -- therefore the calculations of what > 1:24000 > is changes depending on the assumed output DPI. A map of Cambridge > which > is one inch across (300dpi) vs. 3.xx inches across (90.833 dpi) is > going > to have a very large scale diference, sicne "one inch" in the map is > much smaller geographic distance in the latter case. > >> Perhaps I missing something, but the scale is simply calculated as >> the >> the current map width in geographic units/ pixel width. That would be >> the same as OpenLayers, right? > > It's unclear to me how the function you've just shared can relate to > the > style rules without DPI. Resolutions provided in the config file were > provided in scale, the last time I saw them... > > Regards, > -- > Christopher Schmidt > MetaCarta _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
