Faulty behavior after a cut operation

Question

Short explanation of my problem:

On the picture two polygons are shown. The highlighted (yellow) polygon is above the green polygon. Now, two operations are performed.

yellowFeature.geometry().overlaps(greenFeature.geometry()) --> False
greenFeature.geometry().contains(yellowFeature.geometry()) --> True

The results of the two functions were to be expected. Now the yellow geometry is divided into two halves.

Again, the two operations are performed.

yellowFeature.geometry().overlaps(greenFeature.geometry()) --> True
greenFeature.geometry().contains(yellowFeature.geometry()) --> False

The result I did not expect. I expected the same results as before the cut operation. This behavior results in another program to a major problem, since the geometry is correct and the yellow geometry does not overlap.

How can I change this behavior? Does it have anything to do with the precision (decimal)?

My settings: Topological editing is enabled. Snapping tolerance 5px.

Answer 1

By Cut-operation, a new node is created. This leads to a minimal overlap of the two geometries. In this point QGIS is right and there is no incorrect behavior.

In my case, I need to know whether an overlap exists. As a minimum overlap can be ignored, I will calculate the area of the overlapping area.

Based on the above case:

yellowFeature.geometry().difference(greenFeature.geometry()).area()

In short: QGIS is right and I use the workaround for my special case