[Qgis-developer] Saving shapefile and Global CRS

[Micha Silver]

A user posted a problem on the qgis-user list [1] regarding saving a 
shapefile in the AGD84 zone 51 CRS  = EPSG code 20351. (This CRS is in 
the S. hemisphere).

I opened a ticket for this issue [2]

But the problem he raised got me rethinking the Global CRS setting.  
Suggestions have been raised in the past regarding choice of the global 
CRS. Here's another case where someone got tripped up partly due to the 
default setting of WGS84. I think the current behavior is still not optimal.

The different approaches for choosing a global CRS are sometimes coined:
the "ArcMAP way" - the global CRS is set according to the CRS of the 
first layer loaded.
the "GRASS way" - the CRS MUST be chosen at program startup.
the "QGIS way" - the global CRS is always WGS84 until the user sets 
something else.
 
When loading new data layers, we have the option to choose either 
"Prompt for CRS", or "Use the global default CRS". I'd like to suggest a 
parallel setting for the global CRS. That is, the user can choose, just 
like in loading layers, to either "Prompt for CRS" whenever a project is 
started (i.e. whnever QGIS starts up) or "Use global default" whenever a 
project is started. In this second case, the same global default will be 
used for new layers with unknown CRS, and for the project itself.
What problems will this solve?
"Naive" users who mostly work in a single CRS, can set that once as 
their global default, and have all new projects honor that CRS. Then 
loading, saving etc will work transparently.
"Advanced" users who need to switch between different CRS will select to 
be prompted each time, then QGIS will prompt at every program startup 
(and every opening of a new project) which CRS.
I think an arrangement like this will help float to the surface some 
workflow problems that get hidden under the Global CRS setting.

Regards,
Micha


[1] http://lists.osgeo.org/pipermail/qgis-user/2010-September/009649.html
[2] https://trac.osgeo.org/qgis/ticket/3017
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