[Qgis-developer] Re: [Qgis-user] CRS for a start

[Micha Silver]

On 22/03/2010 01:14, Carson Farmer wrote:
> Hello All,
>
>    
>> MN>  I mean in QGIS I can open now a holiday photo, go to layer properties
>> MN>  and get an impresion from it's metadata, that it is already
>> MN>  georeferenced:
>> MN>  "Layer Spatial Reference System:
>> MN>  +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"
>> MN>  which is of course not true. But we have to think about novice GIS
>> MN>  users who might either go dizzy or get bad habits.
>> I agree, the layer properties should not use this as default if prj is
>> missing or should clearly indicate somehow that this is a guessed CRS,
>> not necessarily a real one.
>>      
> I agree as well. In case of no prj or other CRS information and no
> default CRS defined, it would likely be best if the CRS was set to
> "Unknown (Assumed Geographic)" or something like this. It wouldn't be
> too hard to add this to the current CRS db as an additional available
> CRS, and when users have a quick look at a layer's CRS, they will
> instantly see that they have to properly define the CRS if they want
> to use the layer properly.
>
>    
Thanks for bringing this issue up again. (It's been on the list before 
but I can't find the link just now). The ways to deal with layers of 
unknown projection were named (not by me) the "GRASS way" and the "Arc way":
GRASS forces the user to choose a CRS at program startup, then each 
layer must match that CRS. NO o-t-f re-projection. Arc* starts in the 
CRS of the first layer, then automatically does o-t-f re-projection 
without any notification.
GRASS is a bit more difficult, but better in some ways. Arc* is a bit 
easier but has some unfortunate disadvantages.
The behavior I'd like to see in QGIS is- allow users to choose which 
system they want. It could work well, I think, as follows:

In the Options->CRS tab I can choose a global CRS. Currently this CRS 
applies only to new layers (if I select that option). I would like to 
see an additional option to apply the Global CRS to all new *projects* 
including CRS units.
So after a user chooses a global CRS, he can then select if he wants it 
to apply to all layers with unknown CRS (as is now), and he can also 
choose if it should be the default for all new projects. This would 
serve for those who always work in the same CRS, but not epsg:4326. Then 
there should be a third option, to prompt for project CRS on each 
opening of a new project (aka the GRASS way) for those who jump between 
between different coordinate systems.

Then, as others mentioned, there should be some visual notification that 
a layer will not be visible (i.e. raster in a different CRS) or that its 
projection is unknown.

Thanks,
Micha


> Just my two cents!
>
> Carson
>
>    


-- 
Micha Silver
http://www.surfaces.co.il/
Arava Development Co.  +972-52-3665918