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

Peter Körner osm-lists at mazdermind.de
Wed Jul 17 14:40:33 UTC 2013


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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