CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 10/17/2015 05:58 PM, gunshi gupta wrote:
> Hi,
> I have a function written in MATLAB which is clipping a convex
> polyhedron, given an initial convex polyhedron and a plane, and it
> returns the new polyhedron that was formed as a result of the clipping
> (defined in terms of its faces and vertices).
>   This function has been implemented by using the clipPolygon3D function
> that MATLAB provides, internally, by clipping each polygonal face of the
> polyhedron and then doing the necessary computation to combine the results.
> link:
> http://in.mathworks.com/matlabcentral/fileexchange/24484-geom3d/content/geom3d/geom3d/clipPolygon3dHP.m
>
> Now i want to do the same in c++, and preferably using CGAL.
> So
> 1) i have searched and was not able to find a function for polygon
> clipping in CGAL, but i wanted to confirm if that is right since CGAL
> covers quite a wide range of algorithms.
> 2)i have also come across the function "void
> CGAL::halfspace_intersection_3" from section 3D convex hulls in CGAL
> which seems to compute the intersection of a plane and a convex hull.
> link:
> http://doc.cgal.org/latest/Convex_hull_3/group__PkgConvexHull3Functions.html#ga6118d2c46934c541669ab871f8e1fd24
>
> It seems that if i am able to define a polyhedron as a convex hull, then
> from what i understand from the documentation (i understand very
> little), i should be able to do what i described above(polyhedron
> clipping) without having to implement polyhedron clipping through
> polygon clipping. Can someone help me with this/verify if this is possible?
> Thanks a lot!
If the polyhedron is defined as a set of planes, you indeed can use
this function.

If you use a CGAL polyhedron with plane associated to faces, this is
direct.

See this example [1] (only the last line) to see how to associate
a plane to each face.

[1] 
http://doc.cgal.org/latest/Convex_hull_3/Convex_hull_3_2quickhull_3_8cpp-example.html

Sebastien.