[Qgis-developer] About digitizing with GRASS Plugin

Radim Blazek radim.blazek at gmail.com
Mon Oct 19 08:46:49 PDT 2015

On Mon, Oct 19, 2015 at 3:05 PM, m roy <royroge at outlook.com> wrote:
> Il 19/10/2015 12.41, Radim Blazek ha scritto:
>> 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.
> Ok, I see, could it be better to disable point and line tools
> while working with polygons and so on? Just an idea.

You can digitize other types. Say that you add a new point layer, you
can digitize points, lines and areas, but QGIS layer (in non editing
mode) can only display points. Once you close editing, other types
should appear in browser and you can add them to canvas. So you can
digitize (almost) everything at once, but QGIS lets you visualize only
one layer/geometry type when the layer is not edited.

>>> (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?
> Opening the attribute table i get a lot of records with NULL values
> I can imagine that those are for boudaries and the filled ones are
> centroid records (?)

Yes, all primitives are represented as features (that is the only way
to talk with QGIS). Boundaries usually do not have attributes but may
have. For example, if a road runs around a forest, you can use the
boundary of the forest to form forest area and represent the road at
the same time. In such case, the road will have probably different
attribute fields. Currently only one layer of the same map can be
edited at time. Multi layer vectors are not yet perfectly supported

I see the problem with field calculator.

>> 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.
>> Radim
> Well actually in GRASS you simply have different colors based
> on the topology of boundaries, but I understand now,
> given the QGIS layer limitations you explained at point (1),
> that this may not be possible because QGIS layer does not
> have any information about boundaries relative positions.

The information is in topo_symbol field. I could set values of that
field to get visually the same as what is now in GRASS. I just don't
believe that it is better.


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