In QGIS, the Advanced Digitizing tools have some snapping features that I don't see mentioned in the documentation. We know that we can digitize new segments that are perpendicular or parallel to existing segments, or we can lock the new segment to any angle. However, having done any of these, we can also set the length of the new segment by snapping to a variety of "reference points" on other existing segments and vertices. For example, we can snap:
- To the intersection of an existing segment, OR an imaginary extension parallel to that segment (a blue reference line is shown in QGIS):
- To a vertex on an existing segment that would be at right angles to our new segment (here, I've highlighted the reference vertex with a red circle, and added a dotted green line to show the imaginary perpendicular reference line):
My question is, can somebody fully explain how this feature works, or is it documented somewhere? Are there any other ways to snap to a reference vertex or segment, besides the examples I've given?