Computational Geometry in SAGE ( CGAL )

[Nathann Cohen]

Hello everybody !!!

I was once more doing advertisement for Sage, when I met someone who is interested by Sage's Graph library, and would be even more if there were some tools for Geometry. I went to Sage's reference manual on geometry, to learn that we were not that developped in this area.

He then told me there existed an actively developped library in C++ for Geometry, which is called CGAL ( Computational Geometry Algorithms Library ). He added that it was a very efficient one, and that it was a bit difficult to use at first. Sounds like there is some space for Sage there :

1 - We -- need -- some tools in Computational Geometry, especially when all the hard work is already done ( we "just" need to interface it )
2 - We could make this library much easier to use through Sage, as we have plenty of tools they do not have because we're on a much higher level than C++

On the down side, this library is not GPL-compatible ( http://www.cgal.org/license.html ), and so it will have to be included as a spkg. My friend also told me there were other libraries around, making it sound like he was not able to deny their existence, even though this one is for him by far the best.

This library is available at this address : http://www.cgal.org/

There is really a wealth of algorithms we could use.

If anyone is interested in giving it a try, if you know someone who could, well.... Now is the moment to say it :-)

Nathann

[YannLC]

One might also want to look at these existing python bindings:

http://cgal-python.gforge.inria.fr

Yann

[Burcin Erocal]

On Tue, 3 Nov 2009 11:00:33 +0100
Nathann Cohen <nathan...@gmail.com> wrote:

<snip>

> He then told me there existed an actively developped library in C++
> for Geometry, which is called CGAL ( Computational Geometry
> Algorithms Library ). He added that it was a very efficient one, and
> that it was a bit difficult to use at first. Sounds like there is
> some space for Sage there :
>
> 1 - We -- need -- some tools in Computational Geometry, especially
> when all the hard work is already done ( we "just" need to interface
> it ) 2 - We could make this library much easier to use through Sage,
> as we have plenty of tools they do not have because we're on a much
> higher level than C++
>
> On the down side, this library is not GPL-compatible (
> http://www.cgal.org/license.html ), and so it will have to be
> included as a spkg. My friend also told me there were other libraries
> around, making it sound like he was not able to deny their existence,
> even though this one is for him by far the best.
>
> This library is available at this address : http://www.cgal.org/
>
> There is really a wealth of algorithms we could use.
>
> If anyone is interested in giving it a try, if you know someone who
> could, well.... Now is the moment to say it :-)

Disclaimer: I don't know much about the tools/software available in the
computational geometry field, so don't take this as an endorsement of
CGAL. :)

I was talking to someone about CGAL last Sunday, and ended up making
a (very experimental) spkg:

http://sage.math.washington.edu/home/burcin/cgal-3.5.spkg

There is also a notebook worksheet, which has enough cython
wrappers to create a bivariate polynomial using CGAL here:

http://sage.math.washington.edu/home/burcin/cgal.sws

The worksheet is an ugly hack, just to demonstrate what can be done
with cython.

Cheers,
Burcin