[Qgis-user] Split features tool behavior

[Bernhard Ströbl]

Hi Andreas,

I have no problem with invalid geometries in my PostGIS test layers with 
split parts using QGIS 2.14.15 on Linux.
Without having your data I cannot tell why yours are invalid.

Anyway you might try DigitizingTools plugin which has a tool that 
deletes a part of a multi feature and inserts it as a new (single-part) 
feature which might be easier to handle. You can later merge it to any 
feature you like. There is also a tool to fill gaps between features 
with a new feature.

Bernhard

Am 30.05.2017 um 16:41 schrieb Andreas Wicht:
> On 29 May 2017 at 13:16, Andreas Wicht <a.wicht at gmail.com> wrote:
>> On 28 May 2017 at 14:43, James Wood <jwood911 at gmail.com> wrote:
>>> On the digitizing toolbar, try "Split Parts" instead of "Split Features" on multipart polygons.
>>
>> Thank you for the hint, James. Somehow I always thought that this
>> function is only suitable for separating an existing part from a
>> feature (never used it though).
>> Yet, if you cut a polygon with the "Split Parts" tool, the output will
>> be an invalid geometry (I observed self-intersections). This as well
>> can not be the intended behavior. I could observe those errors in
>> simple scratch layers as well as in PostGIS layers.
>>
>> Has anybody else experienced this behavior?
>
> Is my assumption right, that according to this issue
> (https://issues.qgis.org/issues/12799) the current workflow would have
> to look somewhat like this:
> - use split parts tool to split the multipart polygon
> - delete the newly created part (-> invalid geometry) using the
> "Delete Part" tool
>
> either
> - create a new feature/new part (depending on the use case) inside the
> hole created by deleting the part
> - optional: attribute merging with other features surrounding the new
> feature (depends on the complexity of the attribute table)
> - change desired attribute(s) (which led to the decision to separate the area)
>
> or
> - use the "Reshape Features" tool to enlarge a neighbouring polygon by
> the cut off area
>
> or
> - create new feature inside the hole and merge it ("Merge Selected
> Features" tool) to enlarge a neighbouring polygon by the cut off area
>
> Isn't that a bit too much post-processing for that cause?
>
> Any thoughts?
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