Understanding Join Attributes by Location in QGIS?

I wonder if there is somewhere an explanation for the parameters that can be set when running the Algorithm "Join Attributes by Location" in QGIS 2.18.

I had a look here:

but there is no explanation. Any hints?

Answer

Don't think the QGIS docs has something as detailed as what is shown in the link in your comment (here is the link for English speakers). I would assume the terminology would be pretty much similar if not the same.

However, the tool uses the QgsGeometry Class which for each geometric predicate has the following basic description:

• intersects - Test for intersection with a geometry (uses GEOS)


• contains - Test for if geometry is contained in another (uses GEOS)


• disjoint - Test for if geometry is disjoint of another (uses GEOS)



• equals - Test for if geometry equals another (uses GEOS)


• touches - Test for if geometry touch another (uses GEOS)


• overlaps - Test for if geometry overlaps another (uses GEOS)


• within - Test for if geometry is within another (uses GEOS)


• crosses - Test for if geometry crosses another (uses GEOS)

To elaborate on the answers given above, the geometric predicates of QGIS (via GEOS) utilise the spatial predicate definitions of DE-9IM. The following link provides the detailed explanation of each of the common predicates: https://en.wikipedia.org/wiki/DE-9IM#Spatial_predicates