CGAL users discussion list

[Cody Rose <>]

In my experience, using the halfspace constructors took substantially longer.

Cody

On Nov 7, 2013, at 2:16 AM, ChaoM 
<>
 wrote:

> 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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