CGAL users discussion list

[ChaoM <>]

Hello Sebastien: 
        
  Thank you for the code about "Nef to solve 3D boolean Operation " several
months ago. And I have used this method solving a lot of problems. But I
currently meet a new problem which confused me for several days.The Problem
is about the 

costing time. 
As you know, my goal is do the 3D boolean Operation between several models,
these models consist of a lot of triangles. To finish my goal ,I use
exquisite models, each model consists about 600 triangles, 300 vertex, so
when I wanna to 

union 3 or more models together, the total triangles are about 2000. 
I do as your suggestion! Firstly, create polyhedron;Secondly ,convert
polyhedrons to OFF files;Thirdly, the problem comes up, each OFF file
contains 600 triangles and 300 vertex, when converting to Nef polyhedron, it
costs about 2.5mins, 

when I need to do the conversion 3 times, it costs about 7.5mins, it's too
long! 
Trying to improve efficiency of converting OFF to Nef, I replace the "Exact
predicates exact constructions kernel" with "Gmpz kernel", but it cost me
more long! 

Number of Model Total triangles Total vertex    Time of Poly to OFF(seconds)
OFF to Nef(seconds)     Union(seconds)  Nef toPoly(seconds) 
       2             1296           652                 0.14     311.33  
16.06   0.468 
       3             1944           978  0.156   424.72  35.42   1.047 

I research the mannul of CGAL, and read the concept of Nef polyhedron, find
that there are two ways of constructing Nef polyhedron. One way is you
suggest me , convert polyhedron to OFF, convert OFF to Nef. Another way is
opetating halfspaces by unary opreation. So I wanna to know 2 problem: 
1、 How to improve efficiency of converting OFF to Nef when there are 3 or
more models needed to union? 
2、 Whether I can  use the second way to construct Nef? 

 Since I know you are a exexpert on the 3D ,I hope you can point me out when
you are not busy! 
    Thank you very much! 
   ChaoM



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