- 74 - 
Fig.2 : Theodolite with CCD camera 
Fig.3 : Laser 
3. LASER SYSTEM WITH ROTATING LASER 
paralax. The first image with a laser trace is used as a base 
measurement and, however, the distance y 0 between the base 
and the object is known by using self-reflecting distance 
meter. For each image the rotating angle is recorded. Further, 
the distances to the object point are computed from paralax and 
the final 3D co-ordinates are determinated from rotating angle. 
The system is fixed on a platform and the platform position 
must be observed by using a total station. For this reason three 
reflecting prisms are added to the platform. The scheme is 
illustrated on fig.2. From a technical reasons it is better, when 
the camera is stationary and the rotating device is equipped by a 
prism. 
jgÊÊ 
r 
Fig.4: : Optical device (for line track) 
Fig.5: : Laser point track on the wall 
Mathematically, the method is based on measurement of 
horizontal paralax of laser track centre. The first image is used 
as a base measurement. The difference between a laser track 
centre on the first image and the next images gives the paralax. 
The b is the known base distance and it is know, y 0 must be 
measured at the beginning of the experiment. The camera axis 
is perpendicular to the base. In this case we can use an equation 
for normal case of terrestrial photogrammetry. For this method 
the relation to terrestrial photogrammetry is evident. 
y ±= (fy_ 
b p ’ 
( 1 ) 
From equation (1) it is clear, that it is not necessary to know the 
camera constant. Nevertheless, for output precision reason it is 
recommended to use an objective with maximum focus 
distance. The precision of this can be obtained by derivation of 
( 1 ): 
For the second system, a new setting of the elements has been 
developed. There is a rotating base with a convergent laser 
marker and a CCD camera. This model is used for making 
profiles for example in tunnels. The frame CCD camera is 
connected with a notebook and the images are post-processed 
by using special software. The centre of laser track on the 
images is detected with a sub-pixel resolution and the centre of 
laser trace (in image co-ordinates) represents a horizontal 
d y = ~-dp+ ^dy Q - ~j~db ( 2 ) 
b b b 
The precision is given by the element y 0 / b. For example by 
using a CCD with the resolution 640x480pixels, the object 
distance about 4m and basis 40cm, the precision in dy is better 
than 10mm.