[geos-devel] ST_Snap

Sandro Santilli strk at keybit.net
Thu Mar 1 12:48:52 EST 2012

On Wed, Feb 29, 2012 at 08:14:15AM -0800, Martin Davis wrote:
> Snap-rounding is a well-defined technique for eliminating robustness
> problems when overlaying arrangements of line segments.  The
> original paper is by John Hobby; another good paper is this one by
> Goodrich et al:
> http://www.ics.uci.edu/~goodrich/pubs/snap.pdf
> Google gives lots of references to various papers. As always, there
> is a big gap between the papers and a practical implementation!

Great, thanks for the link!
My approach for the incremental topology creation is 
a first-come best-served one. Hot pixels are nodes by definition,
every node of an existing topology is an hot-pixel there.

But it's not easy to determine the grid size, which that paper
is based upon, right ? How close should a segment be to a node
in order to snap there ? In other words, how big is the hot pixel ?

It'd surely be useful to let the user specify such grid (tolerance?)
when invoking GEOS functions.

It's also interesting to note that the floating point number grid 
is of variable size, with cells growing in size while moving away 
from origin.


  |   __/  |    Delivering high quality PostGIS 2.0 !
  |  / 2.0 |    http://strk.keybit.net - http://vizzuality.com

More information about the geos-devel mailing list