Geometry Boost List: [ggl] Snapping

Subject: [ggl] Snapping
From: Barend Gehrels (Barend.Gehrels)
Date: 2009-12-01 04:35:43

Hi Stephen,

Thanks for your document! It is more clear now. In addition to Mateusz 
comments:

1) you mention three methods, but list four methods

2) I don't understand exactly the tolerance neither, can you elaborate a 
little more on geometric tolerance and snapping tolerance, and why one 
must be >10 times the other? Is this the same amount as mentioned later, 
"10x snapping tolerance is a good guide)"? What artifacts would appear? 
Due to numerical robustness issues, or just others? Or maybe you can 
illustrate the tolerance in (one of) the drawings?

3) I don't understand this: "Line to Vertex (LV). It is rare to want to 
do this. But occasionally this is the right answer when a Vertex has a 
higher positional accuracy.", what do you mean by higher positional 
accuracy? You mean that the vertex is more precise, that you know that 
before, and therefore want to snap the line to that? So there probably 
must be a parameter (or more) to influence the behaviour of the algorithm?

4) What will happen if a vertex is not projected on the line segment? 
Within all drawings, it is on the line segment, but what if it is just a 
little above?

5) What will happen if two vertices are within the snap tolerance, but a 
segment is even closer?

6) what will happen if a point is close to a polygon (with holes), 
closer to one of the holes than to the boundary? Will it first detect 
the best-vertex-to-snap-to?

Regards, Barend

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