# [vtkusers] Marching lines algorithm

Wes Turner wes.turner at kitware.com
Tue Feb 26 09:55:32 EST 2008

Hiba,

This is not exactly what you want, but I have previously obtained reasonable
results without specifically calculating the crest-lines.  The application I
was working on used the crest lines of the skull as landmarks for a
deformable registration -- we warped a series of skulls to a single
"representative" skull and the crest-lines provided valuable alignment keys.

The way we did this was to first extract the skull surface using the
marching cubes algorithm.  We specifically chose a threshold to extract out
the bone, but you can choose your threshold to extract whatever surface on
which your crest lines lie.  Given the polygonal surface, the crest lines
need to lie on the boundary between triangles.  We arbitrarily chose a
threshold of 30 degrees between adjacent faces as the level at which we
would declare a crest edge.

Unfortunately, I no longer have access to this code, but I think what we did
was to walk through the surface data extracting cells, and then for each
edge on a cell, did a GetEdgeNeighbors() to find the corresponding cell on
the other side of the edge.  The test for angle between the faces is then
just the dot product of the normals of the two cells.

Again, this is not exactly the crest lines, but seemed to work well enough
in our application.

- Wes

On 2/25/08, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>
> Wes,
>
> You might be able to help this guy.
>
> See you tomorrow.
>
> Bill
>
>
> ---------- Forwarded message ----------
> From: hiba chelbi <chelbi.hibatollah at yahoo.fr>
> Date: Mon, Feb 25, 2008 at 1:22 PM
> Subject: [vtkusers] Marching lines algorithm
> To: vtkusers at vtk.org
>
>
> Good evening eveybody.
> I'm beginner in VTK developpment and i want to know if there is a
> function (an implementation of the Marching Lines algorithm) which
> extracts the crest lines from a 3D image?
> Thank you
>
>
>
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--
Wesley D. Turner, Ph.D.
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x120
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