"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>
> I also thought that the normals of triangles are direction vectors of 'unit
> length' by default, not smaller or larger, but I could be wrong.
[and...]
> *If* the triangle normals are all unit length, perhaps your summing
> operation could be made to... [clip]

[Bald Eagle:]
>
> Triangles typically have a single normal - a vector that is perpendicular to
> its face (in either direction).
>
> The normal can be of any length.
>
> Typically, for lighting purposes, since the normal vector is used to calculate
> how light interacts with the surface, you want them of unit length.
>

Sorry for the confusion, I was actually thinking-- in a muddled way-- of the
original 'source' triangles from Giovanni's STL file.

Honestly, I did not know *what* length such normals there could be-- so I took
one of my 'slice-created' STL binary files made by the 3D SLICER app (mentioned
elsewhere), brought that into MESHMIXER, and converted it to an asci-text STL
file. The triangles-- or each vertex?-- are of this typical form (not
'smooth triangles', as far as I know)...

facet normal -0.107895597816 -0.696702897549 0.709199249744
    outer loop
      vertex 21.3610057831 0.39481022954 -0.11346334219
      vertex 22.4441795349 0.273843616247 -0.158073753119
      vertex 22.0666675568 -0.210549205542 0.393470913172
    endloop

In POV-ray, I took the 'facet normal' data/vector and ran it with vlength(...)
and #debug. It turns out that ALL of the triangles have a unit-length normal:
<1.000,0.000,0.000>, as vlength reports it.

-----
[off-topic here but interesting}: The MESHMIXER app (also my CURA 3-D-printing
app) shows the STL object to have smooth edges-- even though the triangle
data appears to be 'un-smooth'. I have no idea why. Perhaps those apps are
automatically creating smooth triangles from the data. (Or maybe interpolating
the data from the individual vertices?)

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