http://imagej.273.s1.nabble.com/Saving-a-stack-to-STL-format-tp3682702p3682708.html
> Gabriel,
>
> I don't know of anything both free and good (but there are commercial
> packages of varying quality).
>
> Given that the spec is fairly open and not too difficult to understand, it
> shouldn't be too hard to hack up a couple of methods:
>
http://en.wikipedia.org/wiki/STL_%28file_format%29>
> I have in mind that Bene's 3D Viewer stores surface meshes as sets of
> Point3f's, each of which represents a vertex of a triangle. The triangle's
> normal can easily be calculated from the cross-product of two edges. Then
> it is just a case of writing out the file in the appropriate format.
>
> Looking at the 3D Viewer code, the best place for such a method is probably
> the MeshExporter class. I know Bene is pretty busy right now and so am I,
> but this would be a very useful function for users of the viewer (I have
> wanted it myself in the past).
I wrote the MeshExporter class. Let me know if you need help with it.