[postgis-users] A question on ST_RemEdgeModFace usability

Sandro Santilli strk at keybit.net
Thu Apr 12 22:32:58 PDT 2012

On Thu, Apr 12, 2012 at 10:54:45PM +0200, Jose Carlos Martinez Llario wrote:

> In fact, for editing topogeometries without using primitive commands
> I was thinking in:
> 1.- Delete the topogeometry
> 2.- Remove the primitives which depend just on the geometry deleted.
> 3.- With totopogeom insert again the whole geometry

NOTE about (2) : no primitive "depend" on TopoGeometry,
it's the other way around. 

> I know this procedure is not optimized at all but maybe this way
> (with a new function which does this work)  one can avoid the
> complicated task about using primitive editing commands and to edit
> the relation table manually.
> I have the feeling I not taking into account many things though.
> What do you think about this procedure Sandro?

I think the idea should be that of _never_ removing primitives unless
really doing spring cleanups / garbage collection.

Editing a TopoGeometry should be seen as modifying the list of primitives
it is defined by. So in Andrea's case it was _adding_ a face to the list
of defining primitives. And when you want it to shrink but you're missing
a face you can split an existing one (your TopoGeometries won't change

This is about what would happen in your procedure, if you drop step (2).
The toTopoGeometry function will only _add_ primitives, never drop them.

I can see it would be beneficial to have user-friendly functions to edit
a TopoGeometry definition. I've actually been also thining about an UI 
from qgis to do that: something that lets you toggle inclusion/exclusion
of candidate primitives from a TopoGeometry with mouse clicks.


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