Re: [boost] Is there any interest in a template geometry library?

From: Barend Gehrels (barend_at_[hidden])
Date: 2008-01-17 11:25:57

Hi Fernando,

Fernando Cacciola wrote:
> Hi Barend,
>
>   
>>> See:
>>>
>>> http://www.cgal.org/philosophy.html
>>>
>>>       
>> Thanks for the clarification. The library uses the epsilon for floating
>> point comparisons. Your will see it next week, but it is like this:
>>            inline bool operator==(const point& other) const {
>>                if (std::numeric_limits<T>::is_exact) return m_x ==
>> other.m_x && m_y == other.m_y;
>>                else return abs(m_x - other.m_x) <
>> std::numeric_limits<T>::epsilon() && abs(m_y - other.m_y) <
>> std::numeric_limits<T>::epsilon();
>>            }
>>
>> If this approach is not enough
>>     
> Indeed, is not enough.
>
>   
>> you can please help us to make it more
>> robust because I agree, the library should handle these issues and not
>> the user because that is not possible.
>>     
> Yes, I can help you.
> The very first thing you need to do is understand the problem and why that 
> approach is insufficient.
>
> Have you read the sample discussion I posted before? that should get you 
> started.
>
> http://tinyurl.com/2os9co
>   
OK, thanks for your offer. Let me first finish the preview, it will take 
me too much time if I dive into this at this moment. I glanced through 
the discussion and to the philosophy page of CGAL, thanks.

>>> If the library *unnecesarily* fails to produce correct results because of
>>> numerical issues then it's not 'simple' but 'simplistic'.
>>>
>>>       
>> OK, tell me next week if it is bright and simple or just simplistic, I'm
>> curious.
>>
>>     
> You are using the so-called epislon-geometry approach, so I can tell you 
> now: this is simplistic ;)
>
> Feel free to contact me directly if you want, though it might be interesting 
> to discuss it on the list becasue this is not a problem specific to 
> geometric computing but any computing sensitive to round off.
>   
Thanks again, I surely will come back to this.
Barend Gehrels.

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Barend Gehrels, Geodan Holding b.v., Amsterdam, The Netherlands, www.geodan.nl