[vtkusers] The VTK Journal-New Submission

[Bill Lorensen]

The OBJExporter could be refactored to use the OBJReader internally.
Then there would be no code duplication between the Exporter and
Reader.

On Mon, Feb 1, 2010 at 7:35 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
> 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
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