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["naresh" <>]



Hi

 

Basically i have 100 silhouette from 2d images and want to build 3D Polyhydron using Visual Hull. I am trying demo which given nef_3 package.

 

 

Let me know if you need anything more ....

 

 

Alex

 

 

----- Original Message -----

From:

To:

Sent: Monday, May 11, 2009 5:53 PM

Subject: Re: [cgal-discuss] Nef_3 Question

You have to be more specific. The operations themselves have an overhead, because they
allow all degeneracies and use exact arithmetic. We would like to offer more flexibility, here,
but it's unclear when we find the time to redesign the data structures.  In the current state, you
can win much by a) using the perfect kernel (which often is the Extended_predicates_exact_constructions_kernel), and by b) performing the operations in
the optimal order. So, if you give me an idea of what operations you perform, I might give you
a hint on how to save time.

Peter

-----"naresh" <> wrote: -----

To: <>
From: "naresh" <>
Date: 05/11/2009 01:10PM
Subject: Re: [cgal-discuss] Nef_3 Question



Hi Peter

>> We use a kd-tree for point location and ray shooting. But I guess
>> that was not what you were asking for, was it?

You are right. Basically I read in Geometeric Tools by Eberly about BSP tree. Acording to him BSP tree will faster then linear intersection.

But you said it use Kd-tree so it will do same Job as BSP so speed will be same.  In fact i was trying to search why CGAL implemetation of nef_3 is slower.

BTW. Since you are the auther let me ask .

Is there any method i can increase speed because my application has lot of operations. ?

Alex

----- Original Message -----

From:

To:

Sent: Monday, May 11, 2009 3:51 PM

Subject: Re: [cgal-discuss] Nef_3 Question

We use a kd-tree for point location and ray shooting. But I guess
that was not what you were asking for, was it? Look into
the manual to get an idea of the data structure, or have
a look at the papers on our implementation for a deeper
insight.

http://www.win.tue.nl/~phachenb/Nef/Nef3D-DataStructureAlgorithms.pdf

Peter

-----"naresh" < > wrote: -----

To: <>
From: "naresh" <>
Date: 05/11/2009 10:52AM
Subject: Re: [cgal-discuss] Nef_3 Question

Hi

> Unfortunately, the algorithms from the Nef package can not work with
> inexact numbers. I think one would need to use a completely different
> approach to make booleans work with inexact math, but that would
> probably sacrifice correctness in certain cases.

Is the polyhydron intersection is implemented with BSP tree ?



----- Original Message -----
From: "Bart Janssens" <>
To: <>
Sent: Saturday, May 09, 2009 8:57 PM
Subject: Re: [cgal-discuss] Nef_3 Question


> On Sat, May 9, 2009 at 1:20 PM, naresh <> wrote:
>> I am trying to find two polyhydron intersection in nef_3 package. But i
>> found process is very slow because of exact arithmatic calculations.
>>
>> So i have question can i use use inexact arithmatic that gives me speed ?
>
> Hi Alex,
>
> Unfortunately, the algorithms from the Nef package can not work with
> inexact numbers. I think one would need to use a completely different
> approach to make booleans work with inexact math, but that would
> probably sacrifice correctness in certain cases.
>
> Cheers,
>
> --
> Bart
> --
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