CGAL users discussion list

[Nicholas Mario Wardhana <>]

On 12 July 2011 16:53, Mariette Yvinec 
<>
 wrote:
>
>
> yes, vx,vy,vz gives the scale transform on each axis.
> As for the origin, I guess it is assumed to be the bottom, left, back corner
> so that the whole image lies in the positive octant.
> (I was not sure about that, but just get it
> from the code of triliniear_interpolation function in Image_3.h
>

I see, I will try to use those variables and also take a look at Image_3.h .

> one easy test is to compute the value of the function
> at the point you would like to be the center,
> just to test that the value is negative.
>
> Are you sure about the isovalue  " 0.9f " you give
> to define the surface?
> (I don't know what is "f")

Well, since I only have 0 and 1 values in the voxel, so I suppose I
can use arbitrary isovalue as long as it is between 0 and 1, right?
After all my voxel size is already small, so for me slight inaccuracy
is fine.
By the way, 'f' is used to stress that the value that I gave is a
float, not a double. I use that to prevent the accuracy-related
warning.

>
> One question more :
> It seems that you are creating an image from a set of two polyhedron
> and that you are trying to get a surface mesh approximating the polyhedral
> surfaces.
>

Actually I do not particularly target a set of polyhedra, but polygon
soup in general, which might have non-manifold topology. The one I
showed in my previous e-mail is just a simpler data set.

> Note that the Surface mesh generator has also "undocumented features" to
> mesh polyhedral surfaces
> and segmented images that might help you.
> I quote below the user manuel:
>
> The Polyhedron demo has a feature that allows to remesh a polyhedral
> surface, using the 3D Surface Mesh Generator. That has been implemented as a
> special model of SurfaceMeshTraits_3, for polyhedra. That traits class is
> not yet documented because its interface and code have not yet been
> stabilized. It will probably be shipped with next release of Cgal.
>
> The Surface Mesh Generator demo allows to mesh not only gray level images,
> but also segmented images, when voxels are labelled with a domain index.
> Such images are for example the result of a segmentation of 3D medical
> images. This feature is not yet ready to be documented in current release,
> but will probably be in next release of Cgal.
>
> Another way, if you prefer documented stuff, which I can easily understand
> is to get the surface mesh you would like out of the Mesh_3 package.
> For this, it suffices to run mesh_3 with trivial criteria for cells.
>

Ah, I think I missed this part. I will take a look into these classes.

>
> --
> Mariette Yvinec
> Geometrica project team
> INRIA  Sophia-Antipolis
>

Thank you Mariette!

Best regards,
Nicholas