[Qgis-user] vector editing in QGIS - questions and issues (PostGIS biased)

[Maciej Sieczka]

Marco Hugentobler pisze:
 > Maciek wrote:
 >> Marco wrote:

>>> Issue 2:  a) Could be a bug, I have to check that.
>>>
>>> b) Possibly qgis makes a polygon during intersection removal where
>>> postgis enforces a multipolygon.

>> Should QGIS enforce *polygon* then, instead of obeying the layer's
>> *multipolygon* geometry type? I think it shouldn't.

> I also think so. 
> Internally, qgis makes a polygon first, but it should make a multipolygon 
> consisting of one polygon if the layer type is multipolygon.

OK. Shall I fill a report? Same as for other issues we agree they are 
bugs in this thread?

>> But no layer in the project has the individual snapping set - no layer
>> is checked in the "Project Properties>Snapping options"! The default,
>> QGIS-wide snapping setting should take effect for layers which don't
>> have an individual snapping set - but it doesn't. This does look like a
>> bug to me. If it isn't, what is the point of default project-independent
>> snapping setting?

Before you read on: NOTICE - I'm assuming that snapping = 0 is no 
different than snapping "disabled". Is this correct? If it is, maybe it 
would be better to remove the snapping checkbox for layers and use 
spinbox with numbers only to simplify the dialog?

> Ok, I see what you mean. In the snapping dialog of the project should be 
> inserted the default snapping settings (which is snapping to the active layer 
> with the default snapping tolerance) in case the snapping dialog was not 
> changed already.

Yes.

> Otherwise, if a user changes any project property and clicks 
> ok, the snapping will be off for all layers.

I think differently. As long as default QGIS-wide snapping is !=0, all 
layers which don't have inddividual setting set by the user, should have 
snapping set on equal to default setting - unless the user manually 
disables snapping for the given layer.

> I don't think that unchecked layers should automatically have the default 
> snapping tolerance.

Then what is the point of default snapping setting at all? Look - as 
long as you don't enter project properties and click OK, the default 
QGIS snapping is on for all layers in the project. Once you go to 
project props. and click OK, all snapping is suddenly disabled, although 
you did not modify any setting related to snapping. Imagine a user 
trying to guess what happened.

Note also that this was different in QGIS before introducing individual 
snapping setting per layer. You only had the QGIS-wide snapping setting, 
which was always active, for all layers. Now as soon as you go to 
project settings for whatever reason and press OK that snapping is 
disabled. This should be avoided.

> Because it is possible that a user don't want to snap to 
> some layers at all.

The user can disable snapping for a certain layer, if he needs to.

Another thing - IMO users more often need snapping than they don't. Help 
users not to digitize overlapping features by default, eg. promote using 
snapping rather than not using it. I'd be also in favor of enabling the 
QGIS "topological editing" feature by default.

What I hate most in GIS are all those overlapping polygons and lines 
which I have to tediously correct topology for, re-calculate their area 
and length, explain the vendor what is wrong about his data. Please 
promote topological practices.

Maciek