International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
Figure 1. The frame of the measuring system. 
moving satellite. The light level can be adjusted to get the best 
conditions for the detailed measurements using the satellite. 
The measurement table is a light coloured plate. It can be 
covered with a dark coloured canvas, if necessary, to make 
measurement of light coloured objects easier. 
2.1 Outer system 
The outer system defines the coordinate system of the entire 
measurement system. It contains four or more cameras 
arranged into a convergent rectangular block, so that the targets 
in the satellite cover can be seen from at least four cameras in 
every possible satellite position. 
Four cameras equipped with wide-angle optics are sufficient to 
achieve 0,25 mm measurement accuracy in the object for a 
system capable to measure objects of size 3,0 m x 2,0 m x 0,1 
m. 
2.2 Satellite 
The satellite, or the inner camera system consists of four 
cameras, too. They are located beneath a rigid carrier plate, 
which is mounted on a linear motion system. The cameras form 
a convergent, square block, size of which is about 0,4 m x 0,4 
m. The distance from the cameras to the measurement table is 
about 0,3 metres. The distance to the actually measured object 
surface is slightly shorter, depending on the thickness of the 
measured object. The relative orientation of the satellite 
system is known from camera calibration. 
The upper side of the satellite carrier plate contains several 
circular white targets on a black background, as seen in Figure 
2. Their optimal size and mutual positions depend on the 
resolution of the outer cameras, the geometry of the outer 
block, and their distance to the object surface. In Figure 2, the 
diameter of each target disc is about 80 mm. 
The targets should be clearly visible and measurable in as 
many outer cameras as possible. For this purpose, coplanar 
targets are easiest to use. Targets distributed in 3-D may cause 
484 
  
Figure 2. Targets on the satellite cover. 
occlusion problems, and make the use of more sophisticated 
measurement algorithms necessary. 
The error made in the determination of the satellite's 
orientation is propagated to the final measurement values the 
more, the larger the distance between the satellite cover targets 
and the object surface is. Conversely, the more targets there are 
in the satellite, and the wider they are distributed, the more 
accurate the final measurements are, too. To get approximately 
the same 3-D accuracy for the satellite targets and for the final 
measurements, the area covered by the targets should have a 
diameter that is at least twice as large as the distance from the 
satellite's target plane to the measured object surface. If the 
object surface is, say, 0,4 meters below the satellite cover 
plane, then the area covered by the target centres should be 
about 0,6 x 0,6 m?. 
2.3 Lasers 
There are also two laser projectors mounted in the middle of 
the satellite cameras, beneath the satellite carrier. They are 
used to make profile measurements by projecting two mutually 
crossing laser lines on the measured object's surface, or in a 
hole like shown in Figure 3. The laser powers can be adjusted 
according to the measured object surface material. A dark 
object surface may require more power than a light coloured 
object. In this system, the laser light planes have fixed 
orientations in the local satellite coordinate system. Depending 
on the orientation of an edge, the profile of which has to be 
measured, the system can decide optimal satellite positions for 
the measurements. 
  
Figure 3. Two laser profiles in a machined hole. 
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