[Qgis-developer] Thoughts about multi-type tables in QGIS

[Régis Haubourg]

Hi, 
we must clarify some things in this topics:

 - Mapinfo handles only one geometry columns per table, but authorize mixed
geometry types inside of it. To me, there is no doubt we MUST NOT do this.

 - Spatial DB's recommend non mixed geometry types, but authorize mixed
collections, even if working with them is a lot more difficult and ends up
in separating feature type before using spatial operators. User is free to
add several nullable geometry columns to a table-class, or choose any
physical modelisation he wants. It is easy to make views or queries to show
a one geometry table to QGIS or Mapserver (almost all GIS are one - geometry
limited). We do that a lot (ie tables of watershed's here have three
geometry columns: "elementary watershed", "intermediate watershed", "total
watershed"), because it is a good modelisation with only on table to
identify objects.

The question here is how to handle to tables with more than one geometry
columns. By now, we need to avoid showing those geometry as WKT strings > 
this kills QGIS attribute table.

Using additionnal geometries to handle labeling paths is an interesting
path. FYI I am about to have a contractant work on a QEP (only a QEP by now)
on how to improve labeling with Callouts feature, paths storage for
annotations, manually curved labels, and map mask, masking labels too. ie:
"how to port easycustomlabeling and mask plugin nicely". We could discuss
the technical solutions there. 

Except for those underground solutions, I don't see how handling multi
geometry columns in QGIS GUI will improve user experience, without creating
some caveats and traps. Maybe some visual mockups can help here.  I agree
with Bernhard that we probably have more urgent features for basic GIS uses. 

Cheers,
 Régis



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