RE: How to read the normal vector

From: Anshuman Razdan (
Date: Mon Jul 26 1999 - 10:20:55 EEST

Usually (if the file is corectly generated) the triangles are in counter
clock wise direction. so you can create two vectors by subtracting vertex 0
from 1 and from 2. Take a cross product and that is the normal vector. You
may want to normalize it before using it. A lot of software wont generate a
good normal or shouldnt be relied upon.


Dr. Anshuman Razdan
Technical Director PRISM
MC 5106 Arizona State University
Tempe AZ 85287-5106
Phone: (480) 965 5368
Fax: (480) 965 2910

-----Original Message-----
From: []On Behalf Of
Wanchai Rattanawong
Sent: Sunday, July 25, 1999 10:46 PM
Subject: How to read the normal vector

Dear RP's List

I try to analyse the facet normal vector from the STL format. This is the
that I exported the file from CAD system to STL file.

solid Untitled1
  facet normal 9.86393923E-01 1.64398991E-01 0.00000000E+00
    outer loop
      vertex 9.73762280E-01 7.40301994E-01 1.35078953E+00
      vertex 1.00078931E+00 5.78139828E-01 1.35078953E+00
      vertex 1.00078931E+00 5.78139828E-01 3.50789527E-01

 The result that I determined from this example, it is not match to the
facet normal
from the STL file. Anyone know how to analyse the facet normal vector,
please let

Thank in advance,
Wanchai Rattanawong
Industrial Research Institute Swinburne (IRIS)
P.O. BOX 218, Hawthorn
Victoria 3122, Australia
Tel:(613)9214 5654 Fax:(613) 9214 5050

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