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

Radim Blazek radim.blazek at gmail.com
Wed Sep 27 04:27:42 EDT 2006


On 9/26/06, Stephan Holl <holl at gdf-hannover.de> wrote:
> Hello Radim,
>
> On Tue, 26 Sep 2006 16:37:29 +0200 "Radim Blazek"
> <radim.blazek at gmail.com> wrote:
>
> > It should be probably a new tool with a new button in toolbox.

Sorry, forget it. It should be an option on the first tab
(currently cat only). The options should be shown/hidden according
to the selected tool. Another option could be snapping mode
(nearest, nearest vertex,...).

> sounds promissing! Can you forsee if this finds some priority on a
> developers (perhaps your) todo-list?

Yes (I foresee), no (priority).

> Am I right, that this needs to be implemented in GRASS first, befor we
> can make use of it in QGIS

No.

> or is this independent from GRASS and could
> be implemented only in QGIS digitize tool?

Yes.

Radim

> Best regards
>
>         Stephan
>
> > On 9/26/06, Stephan Holl <holl at gdf-hannover.de> wrote:
> > > 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
> > >
> > > --
> > > GDF Hannover - Solutions for spatial data analysis and remote
> > > sensing Hannover Office      -     Mengendamm 16d      -
> > > D-30177 Hannover Internet: www.gdf-hannover.de      -      Email:
> > > holl at gdf-hannover.de Phone : ++49-(0)511.39088507       -
> > > Fax: ++49-(0)511.39088508
> > >
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> > >
>
>
> --
> GDF Hannover - Solutions for spatial data analysis and remote sensing
> Hannover Office      -     Mengendamm 16d      -     D-30177 Hannover
> Internet: www.gdf-hannover.de      -      Email: holl at gdf-hannover.de
> Phone : ++49-(0)511.39088507       -        Fax: ++49-(0)511.39088508
>




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