[Qgis-developer] About digitizing with GRASS Plugin

Radim Blazek radim.blazek at gmail.com
Mon Oct 19 03:41:47 PDT 2015

On Sat, Oct 17, 2015 at 10:05 AM, m roy <royroge at outlook.com> wrote:
> I ran some test with GRASS Plugin in particular
> digitizing some vetor layers. Given that is
> quite nice how well it's already integrated with QGIS
> edit tools, I found some minor issue, this may be
> by design but i'm saharig my thoughts *(IMHO)*, hoping i'll
> find some time for further testing.
> (1) *Create new GRASS vector layer in QGIS*:
> If I understand well we should use the browser panel contestual menu,
> i see there are three options ( New point layer, new line, new polygon);
> anyway GRASS vector format AFAIK has no such distinction given
> that any vector layer can contain any geometry type.

Yes, GRASS vector can have more geometry types and you can digitize
all types in QGIS. QGIS layer however, supports only one geometry
type.  It is not possible to add in QGIS a layer without a type. So
when a new empty layer is created, a type must be chosen. The type
selected by user is only used for the layer added to canvas/legend,
the created vector map is empty.

> This can be confusing, developing some kind of hybrid between the shapefile
> and GRASS own vector format, will also "invalidate" all
> existing GRASS documentation about vector editing and GRASS
> vector format. We'll need to be overly zealos to explain when
> and how things work differently in QGIS otherwise it will be quite
> confusing for new users.

I don't think that it invalidates all documents about digitizing, the
principles and the format is the same. The editing tool is different
and it has some particularities which I'll describe in QGIS
documentation. It is not possible to support all the flexibility of
GRASS vector format through QGIS interface.

> (2) *Attribute table editing*:
> not able to figure out how it works, i managed
> to edit single feature using the "Identify Features"

Changing the values in table cells (when editing) does not work?

> (3) *Symbology of topo feature while editing*:
> Although i think there may be some bugs, I think
> it's better to be consistent with GRASS GIS otherwise
> see the documentation problem at point (1).

Regarding the symbology of boundaries, I am convinced that the
distinction between area/area and area/isle used in GRASS editor is
useless while distinguishing of boundaries with topological error is
essential for effective editing.


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