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

Dane Springmeyer dane at dbsgeo.com
Wed Jul 17 17:41:35 UTC 2013


Chris,

It would be helpful to explain what you've tried already. Mapnik supports proj4 and proj4 understands quite a few projections. I'm no expert in equirectangular projections but https://en.wikipedia.org/wiki/Equirectangular_projection states that this is basically a term for the well know set of lon/lat based geographic coordinate systems.

So, can you try simply changing your Mapnik Map `srs` value to EPSG:4326 or a specific Equidistant cylindrical projection like http://spatialreference.org/ref/epsg/3786/

The specific Mapnik Map XML syntax can be found by following the link for "Mapnik XML" like:

http://spatialreference.org/ref/epsg/3786/mapnik/


Dane


On Jul 17, 2013, at 9:41 AM, Christopher Stevens <chris at christopherstevens.cc> wrote:

> 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.
> 
> 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, 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/
> 
> 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.
> 
> Thanks for the feedback in advance. Let me know if I can answer any questions.
> 
> Best regards,
> 
> Chris
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