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Subject: [ggl] Snapping
From: Mateusz Loskot (mateusz)
Date: 2009-11-30 16:51:46

Stephen Leary wrote:
> Not 100% sure my snapping document got through so here is a link to the PDF.


Nice collection of cases.

A few questions/notes:

1. multi-line should probably read multi-linestring as the GGL multi
   geometry is named, to avoid confusion

2. "snapping a the left to the geometry on the right" - a typo?

3. "Snapping tolerances must be > 10 times the geometric tolerance"

What is the geometric tolerance?
Is it an acceptable deviation of location (of single vertex)
or anything else? Notice, there is no precision model in GGL like in
GEOS. As far as I can understand the matter, it looks for GGL precision
(not accuracy) for snapping would be always based on size and coordinate
space of actual geometry.

4. Related to 3, determining higher position accuracy may be tricky
without precision model, am I correct?

5. I miss a reference to classic papers discussing this matter, also
would be good to have reference or short study on requirements of
numerical robustness. At least a newbie as myself would have chance to
learn some details.

6. Would you consider convert this paper to the Wiki?

Best regards,

Mateusz Loskot,
Charter Member of OSGeo,

Geometry list run by mateusz at