Bug report #12212
Multiparts to singleparts fails with one-vertex lines
|Affected QGIS version:||2.6.0||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:||fixed/implemented|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||20401|
It is possible to construct lines containing just one vertex, by removing all vertices from a line except one.
However, QgsGeometry.fromPolyline() returns "None" if such a geometry is used as an argument.
Therefore, if a multipart geometry contains a feature of which one of the parts is such an (invisible) one-vertex line, the "Multipart to Singleparts" algorithm fails - both the ftools(?)-version and the processing toolbox version.
As far as I can see, fromPolyline() is just redirected to Geom, so perhaps the "Multipart to Singleparts" processing script should work around this issue.
(In a singlepart layer one could just remove all such one-vertex lines by finding all layer features with length 0, but for multipart geometries this of course doesn't work.)
#1 Updated by Daan Goedkoop about 5 years ago
Geom does not allow such shapes; the vector -> check geometry validity tool does indeed report such single-vertex "lines" as an error. So I guess that it is not a bug at all, that the "Multipart to Singleparts" function/script fails in this case.
However, in node-editing mode, still "Check finished (0 errors found)" is displayed in the lower-right corner. Maybe that is not correct, then?
(My QGis interface is in German, I hope the translations back to English make sense)