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)
