QGIS » QGIS Application

There are many projections in Proj4 that are one-way only, ie you can't reverse them easily because they aren't made with a continuous math function but rather a translation table of values. These projections are important for Cartography and are supported by Proj. In order to use them in QGIS you have to reproject with ogr2ogr or gdal on the commandline and then ignore projection settings in QGIS. It would be great if QGIS supported use of them, at least in the Save dialogs, but preferably in the official Projection list. Perhaps a new category of Cartography projections. A user who loads layers with such projections and then tries to enable Projection on the fly to anything other than the matching Projection would get an error box telling them that all data must be in the same projection if you want to use a Cartographic only projection.

• Natural Earth +proj=ne
• Healpix (NASA) +proj=healpix
• Winkel Tripel (National Geographic) +proj=wintri
• Aitoff +proj=aitoff

(The list is much longer)

http://lists.maptools.org/pipermail/proj/2012-May/006302.html
http://gis.stackexchange.com/questions/23089/how-to-define-winkel-tripel-in-proj-4-8-0