CGAL users discussion list

["Tomislav Maric" <>]

Wow, thank you so much!

I will investigate then on writing my own Kernel with the Point type I'm 
using. 

As for the documentation, I can say that I have a somewhat solid C++ 
background, since I'm working with OpenFOAM (a computational fluid dynamics 
library) for the last 3 years, but:

- it is not using STL (nor the concept-refinement-model, there is no 
separation of algorithms from 
  the data structures, etc)
- iterators to a very low extent since the basic data structure is a library 
native kind
  of a vector
- templates are used extensively, as well as polymorphism through virtual 
functions, and 
  other "regular" c++ stuff

In its way, it's perfect at what it does, but I do see the advantages of STL 
based development..

I just want to say that your documentation is excellent, if I'm getting lost, 
its definitely
because of my lack of experience with STL-like codes. When I manage to couple 
OpenFOAM with 
CGAL I would very much like to contribute a how-to or a tutorial to the 
documentation, if anyone
finds this useful... 

OpenFOAM is a code which is used by automotive industry (among others) and a 
lot of institutes
and universities around the world (I've heard recently that it has taken on 
around 40% of the market
share in Computational Fluid Dynamics), but the documentation is 
non-existant, and my daily work
is basically made up of a lot of hours spent on reverse engineering the code. 

I'm sorry for my long E-mail, but I just wanted to let you know that I think 
you should be proud
of both the CGAL project and the documentation you have created! Just my 2 
cents. :) 

Thank you again for your help! 

> ----- Original Message -----
> From: Philipp Moeller
> Sent: 04/24/12 12:08 PM
> To: 
> 
> Subject: Re: [cgal-discuss] using a Point class from another library
> 
> "Tomislav Maric" 
> <>
>  writes:
> 
> > Thank you very much for your advice! :)
> >
> > I have some further questions, regarding the functors. 
> >
> > [1] If I will later on run geometrical algorithms on top of the
> > Polyhedron_3 that uses some other Point class, I will need to provide
> > the functors that are required by the geometrical algorithms, right
> > (e.g. convex hull of a polyhedron with my own Point type)? I have read
> > about this for the triangulation class in the attached tutorial, page
> > 41 (pdf), but triangulation provides a basic template for which the
> > needed functors are defined, and as soon as I plug in my Point type
> > there, everything fits. This is probably not possible to generalize to
> > Polyhedron_3, because there are a lot of geometrical algorithms in
> > CGAL runing on polyhedra....
> 
> It is a problem you bump into with Kernels a lot. While some data
> structures pretend to be agnostic to the kernel and simply accept every
> point type the algorithms that work upon them are not and your Point
> almost always ends up being a Kernel member. So the "easiest" way is to
> define your own Kernel with your own Point type.
> 
> >
> > [2] I'm kind of getting lost with concepts and refinements, because
> > they are intertwining (seem to be to me, I'm a complete newb), how can
> > I best find out what requirements need to be satisfied for certain
> > operations with types? Should I implement the requirements provided by
> > the concept closest to what I need? There seem to be multiple
> > solutions to the same type problems.... and I keep getting lost...
> 
> Concepts try to express what is expected from a type in terms of syntax
> and semantic (sometimes also in run-time complexity). A type that
> fulfills all requirements of a concept is a model of that concept. 
> 
> A function or class template requires its template arguments to be
> models of a certain concept.
> 
> Refinement is somewhat like inheritance between classes in
> C++. Refinement adds constraints and makes the concept "stronger".
> 
> You should try to be exactly as the concept required by the algorithms
> you are going to use.
> 
> Keep in mind that if a function specifies a return type T it actually
> means that the return type of your model must be implicitly convertible
> to T, not exactly of type T.
> 
> Let us know where we can improve the documentation to make some issues
> clearer.
> 
> >
> > Thanks again! 
> >
> > Tomislav
> >
> >> ----- Original Message -----
> >> From: Philipp Moeller
> >> Sent: 04/24/12 10:47 AM
> >> To: 
> >> 
> >> Subject: Re: [cgal-discuss] using a Point class from another library
> >> 
> >> "Tomislav Maric" 
> >> <>
> >>  writes:
> >> 
> >> > I have managed to make Polyhedron work with my Point class, but when I 
> >> > want to read it from an .off file, 
> >> >
> >> > this function:
> >> >
> >> > template < class Point> inline
> >> > Point&
> >> > file_scan_vertex( File_scanner_OFF& scanner, Point& p) {
> >> >    typedef typename Point::R R;
> >> >    typedef typename R::RT    RT;
> >> >    double x, y, z, w;
> >> >    scanner.scan_vertex( x, y, z, w);
> >> >    if ( w == 1)
> >> >        p = Point( RT(x), RT(y), RT(z));
> >> >    else
> >> >        p = Point( RT(x), RT(y), RT(z), RT(w));
> >> >    return p;
> >> > }
> >> >
> >> > from the file "File_scanner_OFF.h" expects my point to have a 
> >> > constructor with 4 arguments. For a simple 
> >> > example Point class that I wrote, I have added this without a problem, 
> >> > but if a Point class is coming from another 
> >> > library, it is a problem. I cannot change the library Point class. 
> >> > What should I do? 
> >> >
> >> > Option 1) Inherit from the Point class of the other library and add a 
> >> > dummy constructor, counting on 
> >> >          implicit casting every time i call a method on the Point to 
> >> > cast it up? 
> >> >       2) Change the .off File_scanner and adapt it somehow? 
> >> >
> >> >       ?) ?
> >> 
> >> The problem is a more complicated. Technically, Polyhedron shouldn't
> >> make any assumptions about the concrete type of Point and use a
> >> Construct_point_3 functor to construct them. This additional functor
> >> would go into the traits as well.
> >> 
> >> As a workaround, I wouldn't change file_scan_vertex but add an overload
> >> to the CGAL namespace, e.g.
> >> 
> >> namespace CGAL {
> >> inline
> >> MyPoint&
> >> file_scan_vertex( File_scanner_OFF& scanner, MyPoint& p) {
> >>  // do my thing here
> >> }
> >> }
> >> 
> >> to change the behavior. This should work as far as I have looked at
> >> things. If not, I'd prefer method 1.
> >> 
> >> >
> >> > I don't need homogeneous coordinate representation of points, so this 
> >> > kind of constructor is not necessary.. 
> >> >
> >> > Working code is attached. 
> >> >
> >> > Thank you! 
> >> >
> >> > Tomislav
> >> 
> >> HTH,
> >> Philipp Moeller
> >> GeometryFactory
> >> 
> >> -- 
> >> You are currently subscribed to cgal-discuss.
> >> To unsubscribe or access the archives, go to
> >> https://lists-sop.inria.fr/wws/info/cgal-discuss
> 
> -- 
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://lists-sop.inria.fr/wws/info/cgal-discuss