CGAL users discussion list

[Greg Fokum <>]

Hello 

I thank you for your mail and your suggestion. If it was a
 simple straight tube, I can just use a plane. I am not sure I explained
 the problem clearly but take a look at this attachement. Given the 
brown tube 3d structure, I want to obtain the blue tube section of it. I
 cannot just use a plane for that ( I could if I knew how to find that 
orientation of plane programatically) but suppose I don't do that, how 
can I cut and extract the blue section from the brown one ?

In the second side of the illustration I think it is possible to 
first model my bent tube as a straught tube then just use a plane with 
its normal along z and do the clipping. The question is how to map the 
bent tube to a straight tube to allow this ?

I will be very grateful for some ideas

Thank you

GT

On Mon, Feb 6, 2012 at 7:43 AM, Sebastien Loriot (GeometryFactory) <> wrote:

Can't you cut by planes and then discard parts you are not interested in (for example discard those that are not in contact with both planes)?

You can use the AABB tree for doing the intersection with a plane.

see:
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/AABB_tree/Chapter_main.html

You can also have a look at the AABB_tree demo where the intersection
polyline of a mesh with a plane can be computed
(Algorithms -> Cut plane -> Intersection; keep 'Ctrl' while manipulating
the arcball to move the cut plane).
.

Sebastien.

On 02/02/2012 07:51 PM, gregthom992 wrote:

HEllo experts

my task at hand is to subdivide a cylindrical object into shorter segments.
My cylindrical object is a mesh oriented along the z-axis with triangles and
edges but it sort of bends like an N at a certain points. Now I want to
obtain a section of the bended cylinder. I could simply clip with a plane at
a certain z distance along the length but my trouble is clipping this way
will yield a funny section if I clip it a the level of the "N" bend. Does
anyone how some ideas how to go about obtaining a single continuous section
of such a shape using CGAL ?

In the image the black lines are clip planes
In the attached image the shape is what I want to extract various sections
of but because the shape bends on itself I get two pieces, however I wanted
just one continuous section from the start through the end to the second
intersection with the clip plane B.

http://cgal-discuss.949826.n4.nabble.com/file/n4352427/test.jpg ?

Thank

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