6

Working with QGis and data from Natural Earth I would like to prepare a world map (1:50 000) for a globe that can be printed in 6 segments, which glued together build a ‘sphere’ (ball) according to the following graticule:

6-lobe printing layout for ball graticule

What projection would you recommend (Winkel tripel?) and how can I export the result (probably segment by segment?) via the print composer to a vector graphic program that allows me to generate the final printing layout (CMYK)?

I am not (yet) an experienced GIS user; the result will be used as teaching aid in poor South American schools.

  • not exactly the answer to your question, but have a look at gene keyes and Dan S. answers on gis.stackexchange.com/questions/1775/… – radouxju Aug 18 '15 at 5:31
  • It's been discussed a few times on Cartotalk and on the older Esri forums, among other places but I'm having problems finding the actual threads. A colleague in the past has said to use polyconic, but you might need to use more than 6 gores. Ah, here's one: Globe construction – mkennedy Aug 18 '15 at 17:06
4

This won't be a complete answer as I finally searched the help of a professional to produce the gores with another software. Nonetheless, let me share with you what I (with the help of the links mentioned above and esp. from Hans van der Maarel) found out, in case it is of use to someone:

The right projection is in QGis is "Sphere_Polyconic, EPSG:53021". It does NOT fit the graticule seen above but might still be the better choice: In the graticule above the map has been scaled along the longitudes with 0.9 before the polyconic projection was applied, apparently to 'loose' less information on the globe caps (poles) which are without print.

Each gore has to be handled separately:

Create a custom CRS for each gore (where +lon_0 takes the values of -120, -60, 0, .. for 6 gores)

+proj=poly +lat_0=0 +lon_0=-120 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +ellps=sphere +units=m +no_defs

Polygons for clipping the raster data (e.g. from Natural Earth) of the gore in the wrapping process (import as WKT, save as shapefile and then select as masks layer in Warp_Reproject) like:

POLYGON ((-150.000000000000000 82.000000000000000,-150.000000000000000 -82.000000000000000,-90.000000000000000 -82.000000000000000,-90.000000000000000 82.000000000000000,-150.000000000000000 82.000000000000000))

Then start a project for each gore with the specific custom projection and add your vector layers (e.g. from Natural Earth) with on the fly projection. QGis will sometimes show the map and sometimes not, depending on the scale and area of the map. These difficulties are reduced by loading the vector data in a project with the target CRS instead of changing the CRS afterwards.

A severe problem remained: Natural Earth Raster data for the gore with the data line will show an empty stripe along the 180th longitude after the warping to the polyconic projection.

  • 1
    Which other software did you use? Very good project, would be good to see even more details! – Simbamangu Sep 3 '15 at 13:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.