on parame- 
  
jector 
| 
4 
  
  
  
-04 
-07 
-09 
-03 
-03 
  
  
  
  
bundle ad- 
surement of 
  
camera and 
IT 
the projec- 
intersection 
ctive image 
iced on the 
ition of one 
pointing of 
en the two 
vertical and 
for scaling 
  
  
  
N Laser array co-ordinates + 
Projector calibration + 
Geodimeter angles (H,V) 
Image co-ordinate (i,j) + / 
Camera calibration + / 
Gcodimeter angles (H,V)^ 
  
  
  
AY i Ay 
/ D 
[x, y, z] ———" A 
Z CCD camera zZ Laser projector 
Figure 13: Spatial intersection for position estimation. 
the intersection result. Different measurements to derive di- 
rections of any object point from the two positions contain 
observational and modelling errors, so exact intersection of 
all these rays is very difficult. In this system, estimation of 
the position of a target point is done by defining the middle 
point of the line normal to the two supposedly intersecting 
rays as shown in Figure 13. An intersection parallax 0.25 mm 
was observed during a laboratory test scan of an object at 
4.5 m distance. 
5 CONCLUSION 
Simultaneous projection of a large number of distinct tar- 
get points by diffraction grating based laser diode projector 
provides high accuracy for automatic measurement of a tex- 
tureless object. Development of a camera model for the pro- 
jector, treating it as a virtual camera, improves intersection 
accuracy during three dimensional object space co-ordinate 
measurement as various distortions are taken into account. 
There is no requirement for a three dimensional testfield for 
calibration of the projector and the camera which can be done 
in the field with the help of two known target points. Motor 
driven sensors can be handled remotely to scan large areas of 
object space. The knowledge of regularity of the dot matrix 
over a nearly flat object surface and the results of a suit- 
able threshold for an uniform textured object surface may be 
used as initial estimates for fully automatic image co-ordinate 
measurements by least squares based template matching. 
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