[GRASS-dev] GRASS digitizing; splitting lines does not update the cat!

[Stephan Holl]

Hello Maciej, 

On Mon, 25 Sep 2006 17:22:54 +0200 Maciej Sieczka <tutey at o2.pl> wrote:

> Stephan Holl wrote:
> 
> > while working with a very long digitized coastline I encountered the
> > following problem.
> > 
> > I split the line into pieces in order to give different attributes
> > to different line segments.
> > But when I split the line, the cat stays identical. So whenever I
> > change an attribute of one segment, it gets changed on all other
> > segments too (because it has the same cat).
> > 
> > This is because no new attribute-entry will be created when a line
> > is split and the cat stays identical.
> > 
> > Would this be a big deal to change this? Where is the right place to
> > look at?
> > 
> > My needed behaviour would be that when splitting a line, the
> > attribute-entry gets copied, the new resulting segment gets a new
> > cat linked to the copied entry. The left-of-new-point-segment stays
> > old, the right-of-new-point-segment gets the new cat linked to the
> > new cat.
> > 
> > What do other think? Is this a convnient usecase?
> 
> The functionlityyou are describing would be very usefull for me as an
> option. But the current behaviour should also be still available - it
> has it's own uses.

Yes, you are right.
 
> Currently you can remove the old cat and add a new one, then fill the
> attribute table again. This becomes a problem, when you have, say, 100
> attributes but only wan't one to be different :(.

Exactly.

If someone could point to the place in the sources where to start I
would like to try what I can do.

AFAIK the following steps need to be done.
1) finding the funtion, which does the spliting
2) get maximal category number from db
3) select values from database 
4) assign new cat to new line-part
4) store copy of the values to database table with new category number

> > Could this be done with GRASS/QGIS right now?
> 
> AFAIK same as above. I would love to see such a functionality in QGIS
> Grass edit tool, too.

Yes, thats the place I like to have it too!!

Best regards

	Stephan

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