CGAL users discussion list

[Andreas Fabri <>]

Hi Jeffrey,

you might have a look at
http://www.cse.ohio-state.edu/~tamaldey/paper/curve-skeleton/cskel.pdf
It is also implemented (using CGAL), though not open source code.
Also, I never tried it.

best,

andreas


On 30/01/2013 11:36, Jeffrey Bush wrote:
> Hi,
>
> Thanks for the response. My email was sent prematurely (I was
> mid-sentence). You did answer one question, but there are more which I
> didn't even get to.
>
>
> I am currently working on creating a program that calculates
> cross-sectional areas at various points along tube-like 3D meshes
> (specifically dendrites from neurons). I only just now came across your
> library and am unsure if it has what I need.
>
> I already have the triangulated meshes. First trying to just take
> user-inputted planes and determine the cross-sectional area of the mesh.
> This seems to be quite solvable using the AABB tree as you have pointed out.
>
> Next step is to determine these planes in some automatic fashion. In
> this case I have had a few ideas, many of which I have "disproved" with
> simple 2D counter-examples:
>
>   * (won't work) Take a point and find the cross-sectional area of
>     multiple planes. The smallest is the one that is across the tube.
>     The planes could be searched in a binary-search type method assuming
>     not too many local minimum. However this won't work at all if the
>     tube is shrinking/growing near the query point.
>   * (won't work) Take the normals in the area of the query point to
>     determine how to orient the plane so it is perpendicular to the
>     tube. However since the surface can be very irregular (bumpy) this
>     won't work either.
>   * Determine the axis of the tube, then take planes perpendicular to
>     the line. However, then the question becomes how to determine the
>     axis of the tube. Also what if the tube is partially curved?
>
> After all that, an eventual goal would be to fit truncated cones
> (cylinders with non-parallel sides) to sections of the tubes. There
> would have to be multiple per mesh as many of my meshes have branches in
> them (where one tube becomes two) and curves would need to have
> multiple. There would be some tolerance for deciding that a single
> truncate cone is insufficient and that it should be split.
>
> So once again, thanks for your input so far on the AABB tree. It gets me
> part way! Making it at least possible to do manually. If solutions to
> the above don't exist yet I would definitely be willing to contribute to
> CGAL. My own 3D geometry code was very similar to yours before I
> discovered CGAL (without any of the abstraction of different kernels, etc).
>
> Thanks,
> Jeff
>
>
> On Tue, Jan 29, 2013 at 10:01 PM, Sebastien Loriot (GeometryFactory)
> <
>  
> <mailto:>>
>  wrote:
>
>     Using the AABB-tree [1] you can do what you want.
>
>     Have a look at the AABB-tree demo that is computing the intersection
>     with a plane you move with the mouse with a mesh
>     (in CGAL-4.1/demo/AABB_tree).
>
>     Sebastien.
>
>     [1]
>     
> http://www.cgal.org/Manual/__latest/doc_html/cgal_manual/__AABB_tree/Chapter_main.html
>     
> <http://www.cgal.org/Manual/latest/doc_html/cgal_manual/AABB_tree/Chapter_main.html>
>
>
>     On 01/30/2013 02:46 AM, Jeffrey Bush wrote:
>
>         Hi,
>
>         I am currently working on creating a program that calculates
>         cross-sectional areas at various points along tube-like 3D meshes
>         (specifically dendrites from neurons). I only just now came
>         across your
>         library and am unsure if it has what I need.
>
>         I already have the triangulated meshes. First trying to just take
>
>         Jeff
>
>
>
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--
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: +33.492.954.912    skype: andreas.fabri