[Qgis-developer] What is the purpose of turning of 'on the fly' crs transformation?

[Alister Hood]

> Date: Thu, 6 Sep 2012 00:14:04 -0700 (PDT)
> From: Magnus Homann <magnus at homann.se>
> To: qgis-developer at lists.osgeo.org
> Subject: [Qgis-developer] What is the purpose of turning of 'on the
> 	fly' crs	transformation?
> Message-ID: <1346915644405-5000110.post at n6.nabble.com>
> Content-Type: text/plain; charset=us-ascii
> 
> Since 0.7 (?) we have included OTF transformation. In the beginning, the
> code
> was a bit buggy :-), and I believe that was one of the main reason for
> turning it off. Now, it's more stable. So, hwat is the reason for being
> able
> to turn it off now?

Sorry for the late reply, but I find it useful to see quickly whether all my layers have the same CRS or not (which is useful in cases where you want to use a tool where the layers are required to be in the same CRS).
 
> 1) Some use-cases handles 'raw' data where a CRS is not meaningful (or
> maybe
> unknown even).
> 2) To skip the OTF code for stability.
> 3) To skip the OTF code for speed.
> 
> Measruement tools uses OTF code to be able to calculate on an ellipsoid.
> Currently, when OTF is off, we don't allow that but usees planimetric
> calculation only. Is this correct do you think?
> 
> Magnus

Alister