[QGIS-Developer] Dynamic linking a new PROJ.4 problem

[Barry Rowlingson]

Someone on the GIS stackexchange site wants to use the "Authagraph"
projection for maps (its a bit like a Dymaxion):

https://gis.stackexchange.com/questions/266581/how-can-i-use-the-authagraph-projection-in-qgis

I thought this might be as easy as recompiling PROJ.4 with the patches
given in a link on that question, then pointing LD_LIBRARY_PATH on my Linux
box to dynamically link with that instead of my system PROJ.4

My QGIS reports its using PROJ.4 version "493", so I got version 4.9.3
sources and patched it, I can run the newly built `proj` on the command
line and it works:

$ ./proj  +proj=augr +ellps=WGS84
0 0
1408004.57    8254540.11

If I set the LD_LIBRARY_PATH I can see that QGIS has linked to my new
libproj.*.so file, and if I try and create a Custom CRS I can specify
"+proj=augr +ellps=WGS84" and it will convert coordinates in the "Test" box
as it did on the command line, so I know its linking correctly and it
understands the "augr" projection.

BUT... when I hit "OK" on the Custom CRS dialog, I get "The proj4
definition of 'my augr' is not valid" dialog.

Does QGIS have some idea of what is a valid CRS independently of the linked
PROJ.4? Do I actually need to rebuild QGIS with my patched PROJ.4 to get
this to work?

QGIS version is 2.18.14, running on Ubuntu Linux.

Thanks

Barry
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