On 24 Nov 2008, at 18:47, Jay Douillard wrote: > I've added a page to the trac wiki around this topic > > http://trac.mapnik.org/wiki/ScaleAndPpi > Please consider it a first draft!
Great, thanks Jay! Just to clarify, scale denominators (Layer and Rule objects) are both using 'standard' pixel size. I think I got these ideas from SLD spec. I'll need to check. > > ---- > Jay > Regards, Artem > ----- 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 > _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
