rent light, and better ambient light rejection for accu 
rate measurement. 
In the basic geometrical principle of optic triangula 
tion, the light beam generated by the laser is deflected 
by a mirror and scanned on the object. 
A camera, composed of a lens and a positive sensitive 
photodetector, measures the location of the image of 
the illuminated point on the object. The X,Z coordi 
nates are calculated applying simple trigonometric rela 
tionships. 
The error in the estimate of Z is inversely proportional 
to both the separation between the laser and the posi 
tion detector and the effective focal length of the lens, 
but directly proportional to the square of the distance. 
Unfortunately the separation cannot be made as large 
as desired, because it is limited mainly by the mecha 
nical structure of the optical set up and by shadow 
effects. 
Anyway, adopting a synchronized scanning scheme 
large fields of view with small triangulations angles 
can be obtained without loss of precision. As depicted 
in Figure 4, the istantaneous field of view of the posi 
tion detector, defined by P and f 0 , follows the spot as it 
scan the object. The focal length of the lens is therefore 
related to the desired depth of field and not to the field 
of view. 
Laset 
Fig. 3: Synchronized scanner 
This triangulation technique can be implemented using 
a dual axis auto-synchronized scanner (see Fig. 4), by 
which a 3D surface map is obtained as follows: 
1) Scanning a laser beam onto the object with two 
oscillating mirrors mounted orthogonally from one 
another; 
z 
result an ASCII data file of computed (X, Y, Z) object 
points coordinates was produced. 
Fig. 2 : Right image of sample mould 
Finally the corresponding DEM was generated conver 
ting the ASCII file in a GRID data file by the surface 
mapping software SURFER and applying the Kriging 
interpolation to these grid data. 
2. THE LASER SCANNER SYSTEM 
Range cameras based on structured light can generate 
complete image data of visible surfaces that are rather 
featureless to the human eye or a video camera. 
Among the advantages of using a laser source one 
fields, compared with what is achievable with incohe 
Fig. 1 : Left image of sample mould 
(X.Z)