Finding intersection topology errors in QGIS

Question

I would like to find the intersection topology errors in a line layer using QGIS 2.18. In the topology checker I found no intersection errors. I know GRASS v.clean and v.build commands can solve these errors. I found that the Merge selected features tool from advanced editing toolbar (as a side effect) breaks intersecting lines and then using Multipart to singleparts from vector menu gives back the original single line features, but this way the attributes are lost. After selecting all lines and merge them the intersecting lines are broken. I would like to find a the intersection errors without automatically breaking the lines using QGIS. I need something similar to Topology checker.

Answer 1

I found a solution to have a point layer showing the intersection of lines in a layer.

1. make a copy of the original line layer
2. make the copy layer editable and select all features and merge them using the advanced editing toolbar merge selected feature tool
3. extract nodes from the merged layer using Vector/Geometry tools/Extract nodes from the menu
4. extract nodes from the original line layer
5. make a symmetric difference of the two node layers, only the intersections of the original line layer left in the result