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

From: Fernando Cacciola (fernando.cacciola_at_[hidden])
Date: 2008-01-17 11:45:57

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

>
>> 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.

Best

-- 
Fernando Cacciola
SciSoft
http://fcacciola.50webs.com