[vtkusers] The VTK Journal-New Submission

[David Doria]

On Mon, Feb 1, 2010 at 1:59 AM, Alexandre GOUAILLARD
<agouaillard at gmail.com> wrote:
> dear mike,
>
> STL is not a scene format, it never includes cameras, objects, ect
>
> You could find STL specs, but here is a simple wikipedia extract
> (http://en.wikipedia.org/wiki/STL_(file_format)) for your convenience:
> """
> STL files describe only the surface geometry of a three dimensional
> object without any representation of color, texture or other common
> CAD model attributes.
> [...]
> An STL file describes a raw unstructured triangulated surface by the
> unit normal and vertices (ordered by the right-hand rule) of the
> triangles using a three-dimensional Cartesian coordinate system.
> """
>
> VRML and OBJ were defined to include much more than that and the VTK
> implementation rightfully reflects that. Without even entering into
> NURBs and other free forms surfaces, or the group-smoothing, LOD
> algorithms that OBJ format supports, rendering and material
> informations are inherently part of the graphic scene.
>
> again, an extract of the .obj specs, for your convenience:
> """
> Display/render attributes
>
> o       bevel interpolation (bevel)
> o       color interpolation (c_interp)
> o       dissolve interpolation (d_interp)
> o       level of detail (lod)
> o       material name (usemtl)
> o       material library (mtllib)
> o       shadow casting (shadow_obj)
> o       ray tracing (trace_obj)
> o       curve approximation technique (ctech)
> o       surface approximation technique (stech)
> """
>
> Of course,
> 1. if you are dealing with an explicit discrete surface (let's say a
> triangulation)
> 2. If you are only interested in the discrete geometry and topology
> (as in cells, as you are gonna loose the topological information that
> is explicit written as grouping in the obj file),
> 3. assuming that you are dealing with only one surface with a unique
> connected component,
>
> You could write an OBJ file directly from a polydata.
>
> Converting a stack of image to a surface is off topic.
>
> You are right, vtkRendering windows might not be an option on some
> platform. Should you consider another file format to save your model
> to then?
>
> regards.
>
> alex.

Alex,

You are correct. However, the intent was to simply write "simple,
point and triangle only" data to a subset of the OBJ format because I
have run into several cases where this is the only format that could
be read and I needed to write my mesh to it. If there is such a
philosophical problem with it, I will not debate if it should be added
to VTK. But let it live on the VTK journal for others who run into my
situation.

Thanks,

David