[Qgis-user] Using custom projections/transformations from a PROJ.4 init-file

[Kristian Evers]

Good suggestion, but that's not it. I have made tests with simpler transformations as well. Things like "+proj=merc +lat_0=56" (in separate init files with no exotic stuff in it) for instance, which is definitely defined both ways. Same result. Also, the test calculation wouldn't work if that was the case.

Other suggestions?

/Kristian

-----Oprindelig meddelelse-----
Fra: Qgis-user [mailto:qgis-user-bounces at lists.osgeo.org] På vegne af Andre Joost
Sendt: 12. januar 2018 16:19
Til: qgis-user at lists.osgeo.org
Emne: Re: [Qgis-user] Using custom projections/transformations from a PROJ.4 init-file

Am 12.01.2018 um 11:24 schrieb Kristian Evers:
> Hi,
>
> I am trying to define my own "custom projection" by using a PROJ.4
> init-file. The reason I want to do that is that I only want to
> maintain the projections/transformations that I need  in one place
> instead of many. I find the process a bit frustrating since at first
> glance it seems to be working, but then when I try to save it and
> close the custom projection dialog I am told that the definition is
> invalid. As it can be seen on the screenshot below, when I enter the
> PROJ.4 parameters - in this case
> "+init=C:\dev\NordicTransformations\resources\DK:UTM32N" - the test
> works fine but when I try to save it, I am presented with the message
> below. Since the test works the problem is not that the file can't be
> found - it is something else.
>
> I experience the same behavior in both QGIS2 and QGIS3. Is this the
> intended behavior? Is it by design that I am not able to use
> init-files or is this simply a bug? Is there a known workaround?
>
> [cid:image001.png at 01D38B96.E25BF930]
>
> There is no errors in the projection setup in the init-file, which
> the working test transformation proves. The init file in question can
> be seen here:
> https://github.com/NordicGeodesy/NordicTransformations/blob/master/resources/DK.
> I am aware that I can just add the definition of the CRS directly, or
> simply use epsg:25832. That is not the point. I have other more
> esoteric transformations in the same file that is more complicated to
> manage in QGIS itself.
>
> I appreciate any advice and guidance. If this indeed is a bug I will
> gladly help fix it.

QGIS (via GDAL) needs a working inverse projection to be defined. Many 
exotic projections defined in PROJ.4 fail therefore.

I guess the +proj=pipeline definitions spoil that requirement. I'm not 
even sure if those work in command-line GDAL.

Greetings,
Andre Joost

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