[OSM-dev] Plotting data on an equirectangular map, distorted for sphere projection

[Christopher Stevens]

Peter,
Thanks for the helpful info! It's much appreciated (and I just realized I
posted to OSM list instead of mapnik, helpful anyway!).

I'll look deeper into post-render distortion.

Kind regards,

Chris


On Wed, Jul 17, 2013 at 8:40 AM, Peter Körner <osm-lists at mazdermind.de>wrote:

> Hi
>
> Am 17.07.2013 15:41, schrieb Christopher Stevens:
> > Hello gurus,
> > I'm thinking that I may need to find some alternative data visualization
> > software to make this work, but I love mapnik and thought it would be
> > good to start here first.
> Mapnik is capable of rendering data in nearly any possible projection -
> and it can be done with osm-data, too.
>
> On http://polar.openstreetmap.de/ we do a rendering in EPSG:3031
> Antarctic Polar Stereographic projection.
>
> Code and documentaztion can be found here:
> https://github.com/MaZderMind/mapnik-stylesheets-polar
>
> However those projections are applied to the geometries *before*
> rendering out a planar, rectangular image.
>
> > I'm hoping to create a basic themed map of different types of data and
> > plot it on a full-Earth image (I can figure this part out, starter
> > examples cover this as well). The challenge is that I'm then projecting
> > this on Science On a Sphere
> > <
> http://www.spacefoundation.org/visit/northrop-grumman-science-center-featuring-science-sphere/science-sphere%C2%AE
> >,
> > which requires equirectangular images that distort more towards the
> > poles. Here's a quick example of something I made in a 3D program to
> > show latitude and longitude lines (note how the lines and labels get
> > fuzzy and stretched near the poles).
> >
> > http://www.flickr.com/photos/8139783@N08/9305646391/
> This however looks like an post-render distortion, so I'd guess you'd
> have to apply some filter to the rendered mapnik images.
>
>
> > Is there a way to add this type of distortion in mapnik? I'm guessing
> > not as mapnik is optimized for other uses (but who knows). I'm guessing
> > that it would "work" as is, but labels would get distorted (there are
> > work-arounds), and lines would get very thin near the poles.
> I'd bet that it would be better to use sth. like graphicsmagick or a
> custom program with libpng to do the pixel-transformations after the
> rendering finished.
>
> Peter
>
>
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-- 
Christopher Stevens
303.929.7863 cell
www.christopherstevens.cc
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