[Qgis-developer] Help with projections

[Alex M]

The missing worldwide projection is a long standing issue. I can't
recall if there's a ticket (pretty sure there is). The cause is that
QGIS only allows projections that can go both "to and from". Where many
world projection are only "to". The gdal technical term is inverse
transformation. This primarily prohibits data saved in these projections
from being reprojected to anything else. So really just a limitation of
the Projection-on-the-fly.

Some projections include Natural Earth, Winkel Tripel, Fuller, and
Peirce quincuncial. Many of these are actually in gdal/ogr which I use
to transform outside QGIS and then load QGIS and turn off
Projection-on-the-fly.

I have also thought a bit about how spatialreference.org and epsg.io
deal with projections. Having a typical bounding box for each
projection, showing what area it's normally used for and the limits(if
you are trying to reproject into it). If you have those limits you can
also use it to clip things outside the allowed region of the projection
instead of throwing an error for coordinates out of bounds.

Thanks,
Alex

On 01/13/2016 12:41 AM, Andreas Neumann wrote:
> Hi Paolo,
> 
> I think it would be worth to have better projection choice support in
> QGIS. It is really hard to select proper projections, esp. for new
> users. We also lack some useful worldwide projections in our proj4
> database.
> 
> One could have a d3.js based preview for world-wide projections.
> 
> Would be a good thing for a GSOC project, I think.
> 
> Andreas
> 
> On 13.01.2016 09:23, Paolo Cavallini wrote:
>> Il 13/01/2016 08:24, Paolo Cavallini ha scritto:
>>> Hi all,
>>> during courses, a frequent question is how to find the correct
>>> projection for layers without a .prj or similar.
>>> An interesting approach is this: http://projfinder.com/
>> BTW, this particular implementation does not work, as it seems to be
>> strongly biased towards North America.
>> The idea is still valid, however.
>> All the best.
> 
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