QGIS » QGIS Application

see also #4559

don't know if cfarmer is the right person to assign this issue to??

the split feature tool is part of

int QgsVectorLayer::splitFeatures( const QList<QgsPoint>& splitLine, bool topologicalEditing )

(implemented via geos, not via ftools (for what I can see))

the actual bug is that the line is also split on it's self intersections

I'm a new QGIS user and thought I was nuts until I found this bug report. I open a single GPX track in QGIS, convert it to a shapefile, and try to split it into two sections. Before the split feature, the attribute table had 1 entry; after: 75 entries! This is impossible to deal with.

Since this defect is so far down the priority list, is there a workaround we could try in cases where we need to split a self intersecting line? I really don't want to trace new lines over the original GPX/SHP for every subsection of the original.

Thanks

I am setting up Mac OS X 10.9.4 to do QGIS development. I could use a tip or two on where to look to try fixing this issue. Thanks in advance.

The saga tool "split lines with lines" works fine to split lines even if they have self intersections. Perhaps one of the devs could have a look at the saga source code how they manage to split the lines correctly? http://www.saga-gis.org/saga_tool_doc/2.2.7/shapes_lines_6.html

Pedro Venâncio wrote:

Hi,

Please make a test with the two layers I am attaching.

The layer trajeto_completo_2.shp has one single line and the layer percurso_pedestre_2.shp has 2 lines.

Try to make a Split feature in each of the layers.

Making split in percurso_pedestre_2.shp, I get 3 lines, as expected.

Making split in trajeto_completo_2.shp, what happens is that the split is done at all points where the lines intersect.

I thought I was with the problem of this ticket, but more strange is that does not always happen, and the layer in this example is the same, it was only made the split of trajeto_completo_2.shp in another software, resulting in percurso_pedestre_2.shp.

Can anyone see any substantial difference between the two shapefiles that allows explain this different behavior?

I think one way to fix this issue would be through "Enable topological editing" option of the Snapping Options. If this option was active, then it should do the split at every self-intersection, as a network topologically should not intersect.
However, for example in the case of road viaducts, the lines can cross without intersect, since they are at different levels. So, for these cases, the "Enable topological editing" option should be deselected.

This approach fails only because there may be the two situations in the same layer, and therefore may not be very worthwhile.

It is best to avoid it to happen, because to make the split at self-intersections will be enough to import the layer into GRASS, that will automatically enforce topology.

In any case, this issue seems to me to have some priority.

This is still true in QGIS 3.x