Luhmann (2000) reports on accuracy assessment methods for 
3d measurement systems, including automatic or semi 
automatic software. 
Zhou and Fraser (2000) report on a new method for surface 
reconstruction, with good results, but this is not wet 
implemented in a commercial system. 
Most of these cases are completely depended on classical 
photogrammetry. A promising approach is raising using moving 
digital cameras (Heikkinen. J., 1996 and Pollefeys M., et al., 
1999). These techniques focus on a fast and automatic 
production of 3d models for presentations, rather than on 
accurate 3d models. Provided a set of control points and a more 
sophisticated approach to accurate measurements, it is possible 
that this systems will become the industry standard. 
Nowadays laser scanner technology becomes open to public. 
Systems are composed from a laser head with one or two CCD 
cameras and a system (usually an electromechanical arm, or a 
CNC machine), which moves and calculates the head's position 
and rotations in 3d space. The projected laser realize on the 
surface a line (or points) while the 2 CCD cameras calculate the 
position of the well defined line (point) in 3d space using simple 
triangulation. These points are calculated in the head's reference 
system and then transformed in the real world reference system 
through the attitude and position values from the head carriage. 
Density of points and automation are the strong points of such 
systems. The overall accuracy depends mostly on the accuracy 
of the system, which calculates the attitude and position of the 
head in 3d space. Acquisition times are usually long, but 
justified by the huge number of points gathered. 
sizes and lighting conditions. A structured light system, which 
is much closer to author's photogrammetric background, was 
finally chosen from Eyetronics. This system is designed by 
electrical engineers and therefore uses fundamental matrices 
instead of the robust geometrical model of the pinhole camera. 
In principle, the second image of the photogrammetric pair is 
being replaced by a slide projector. The information necessary 
for point calculation in 3d space (x, y pixel coordinates), which 
is extracted from the second image, is now “projected” through 
the slide projector and recorded in a single image. 
In order to make a single scan the relative positions of camera 
and projector must be known. Therefore after positioning 
favourably the camera and the projector so that the projected 
grid has the desired density over the object, a calibration box 
with circles must be photographed instead of the object (fig. 2). 
Due to the known geometry of the box and the circle distance, 
the software can calculate the relative position of camera and 
projector in real world coordinates. 
As the dens grid from the slide project is realized over the 
object, it becomes distorted and photographed using a digital 
camera. During post processing, software automatically locates 
the grid intersections and calculates 3d coordinates of the points 
(fig. 3). Therefore, density of points in the final model is 
depended on the grid density during photography. 
Although computation can be done on site, usually is being 
done back in the office, due to the excessive number of 
photographs being taken in site for obvious reasons. 
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Figure 1 
On left the CNC machine with the double CCD laser 
head used in this project. On the right the laser stripe 
triangulation principle. 
The combination of a CNC (3 axis Denford CNC machine) 
machine with such a laser head (Reversa 10H Laser Head) 
provides very good accuracy. Laser head accuracy is 10 um, as 
reported by the provider, and this is equivalent to CNC 
movements (5 um, using step motor). 
Portable laser scanners are a new trend and address mainly the 
problem of functionality, but they still depend heavily on 
surface matching and positional accuracy over the whole object. 
Their accuracy is somewhere between optical scanners and the 
aforementioned system. 
In any case laser scanners provide exceptional accuracy among 
points in a single scan, for almost all possible applications. 
Figure 2. Set up of camera and projector during Kouros’ plaster 
replica photography in ARF’s lanoratory. 
The process described seems easy and requires almost no 
expertise, but in practice a number of problems arise. 
The automation degree of the system is high. The detection of 
the projected grid over the calibration box and the object itself 
is very good (fig. 3). Material and colour of the object play an 
important role to the procedure. White objects provide better 
contrast for the projected grid in comparison to black. In any 
case a few manual corrections are needed in areas with 
occlusions or steep slopes with respect to angle of view.