[Qgis-developer] Unknown CRS problem

Micha Silver micha at arava.co.il
Thu Jan 6 13:57:31 EST 2011

On 01/06/2011 08:14 PM, Martin Dobias wrote:

> Hi Nick
> On Tue, Jan 4, 2011 at 11:29 PM, Nick Hopton<nhopton at gmail.com>  wrote:
>> When a layer is loaded and QGIS can't determine its CRS it would be
>> preferred if the CRS of that layer was shown as 'unknown', rather than
>> shown as being the default CRS. I know that this causes problems for
>> some newcomers to QGIS.
>> I gather that this question was raised during the Hackfest in Vienna
>> and I wonder whether or not it is being followed-up?
> (I barely remember any discussion on this topic.)
> I agree with you that CRS handling should be improved. Having
> 'unknown' CRS is more useful than assigning a bogus CRS and then
> trying to project it to some other CRS. I think we should remove
> on-the-fly projections option and _always_ do the reprojection of

Hmm.... Some thoughts:
Won't OTF projection of raster always be a heavy computational process,  
slowing down rendering?
Second: To which CRS will this automatic OTF reproject to? The situation 
now is that a new project always starts in EPSG:4326. There's no way 
AFAIK to cause QGIS to always start in some user chosen CRS (other than 
creating a default project in your chosen CRS, then change the QGIS 
shortcut to always start that project.)
Suppose I have some big LandSAT rasters in UTM, and vector layers in 
some other projection. If OTF was always "on" I'd be reprojecting both 
the LandSAT and all the vectors into Lon/Lat WGS84.
THird: Having OTF automatic still won't help users with data that lacks 
a CRS.

First priority, in my mind, should be an option for users to set the 
default *project* projection. For example, in the Options->CRS window, a 
checkbox offering to use the chosen "Global" CRS (which currently 
applies only to layers with unknown CRS) as the default for new projects.


> layers (many times this will be just a no-op). Only layers with
> unknown CRS wouldn't be projected. One problem here is that we haven't
> implemented raster reprojection yet.
> Regards
> Martin
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Micha Silver
Arava Development Co. +972-52-3665918

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