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Re: [cgal-discuss] bug in Loop subdivision


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  • From: "Sebastien Loriot (GeometryFactory)" <>
  • To:
  • Subject: Re: [cgal-discuss] bug in Loop subdivision
  • Date: Wed, 23 Apr 2014 10:21:00 +0200
  • Organization: GeometryFactory

On 04/23/2014 03:39 AM, Ivan Middleton wrote:
I was just comparing the results of CGAL's implementation of Loop
subdivision with my own implementation, and found a very bad error in CGAL.

On line 240 of include/CGAL/Subdivision_mask_3.h we find:

FT Cn = (FT) (5.0/8.0 - std::sqrt(3+2*std::cos(6.283/(double)n))/64.0);

The square root should instead be a squaring operation! (A much more
minor point is that it surely wouldn't hurt to use a more accurate value
for 2pi.)

This number Cn is what's called beta (or n*beta) in most references. See
for instance page 70 of

http://mrl.nyu.edu/publications/subdiv-course2000/coursenotes00.pdf

Best regards,
Ivan


Thanks for the report, it will be fixed in the next release of CGAL.


Best,

Sebastien.




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