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I have QGIS with proj 4.8.0 installed. I'd like to add Winkel Tripel projection which seems to be defined as

+proj=wintri

But that definition string does not work. Is this a bug in my proj version, or what's the correct definition string?

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    Works for me: echo "34 -34" | proj "+proj=wintri" – Paul Ramsey Nov 22 '12 at 4:17
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    Yes, that echos something. But if I define a custom CRS with this string, nothing gets reprojected in QGIS. Guess I'd need some more parameters? – underdark Nov 22 '12 at 6:42
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    @Paul Ramsey: It seems that even though the Winkel Tripel projection is defined in the proj library and can be called from the command line, it can't be used as a custom CRS in QGIS because there's no inverse transformation in the proj library (see lists.maptools.org/pipermail/proj/2012-May/006302.html). And it seems that the inverse transformation isn't trivial (and will always be an approximation...). – Jake Nov 23 '12 at 16:17
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    I think you should write that into an answer, as it is... the answer. The command-line tools also refuse to do an inverse projection. – Paul Ramsey Nov 23 '12 at 17:39
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    As the collegues mentiond above, if you have also with proj +proj=aitoff have the same problems, it is a matter of missing inverse projection see: (+proj=aitoff; Rel. 4.7.1, 23 September 2009 <invproj>: inverse projection not available) and ( invproj +proj=wintri; Rel. 4.7.1, 23 September 2009 <invproj>: inverse projection not available ). Strange but good to know – huckfinn Feb 7 '14 at 23:18
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Summing up the discussion above:

While Winkel Tripel projection is defined in the proj library and can be called from the command line, it can't be used as a custom CRS in QGIS because there's no inverse transformation in the proj library.

The enhancement request to add this functionality has been closed since it seems that the inverse transformation isn't trivial.

  • Could this be different now? I am, with pyproj==1.9.5.1 installed, able to do: pp = Proj(proj='wintri', lon_0=47.); pp(*pp(0,0), inverse=True) which returns (0,0) (to machine precision), i.e., I'm able to reverse the forward transform with the inverse=True keyword. Since this pyproj seems to have the inverse, could QGIS support this now? – Ahmed Fasih May 3 '18 at 1:16

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