2.2 STEREOUTHOGRAPHY DETAILS
4.2.2
StereoUthography
Details:
The"
.STL"
File Format
Introduced by 3D Systems Inc. in 1987, the ".STL" file format has become the de
facto standard, even though other "direct slice" methods have been tried. The" .STL"
method tessellates the CAD model with triangles just like the hexagons and pen-
tagons on the surface of a soccer ball.
The ".STL" file is (a) a header, (b) the number of triangles, and (c) a list of the
triangle description by vertices and the normal vector to the triangle. Table 4.2 shows
the layout. The size of the ".STL" file is (50 x number of triangles)
+
84. Thus a
1O,OOO-triangle
object needs 500,084 bytes.
TABLE4.2
The
N
.5Tl
N
File Format
Entity
Described
by
The header
80 bytes
The number of triangles
Unsigned long integer
(4
bytes)
For each tessellation triangle (50 bytes
of
information)
See below
Floating point integer (4 bytes)
Normal vector
I
Normalvector J
Normal vector K
First vertex
X
Ploanng polnt integer te bytes)
First vertex Y
Flontingpo;ot
integer {4 bytes)
Fint vertex
Z
Second vertex X
Second
vertex
Y
Second vertex Z
Third vertex X
FLoating point integer (4 bytes)
Third
vertex
Y
Third vertex Z
Attribute
Unsigned inleger (2 bytes)