ee. 
ia AW 
wv 
4 
Guehring, Jens 
  
Glass plates 
      
    
Polarizing 
filters 
Light Projected 
source LCD Lens pattern 
  
Liquid crystal 
(a) (b) (c) 
Figure 1. (a) Stripe projection using a two-dimensional LCD.(b) Normal type LCD. 
(c) Cross-pattern LCD. The second glass plate is turned by 90 degrees. 
In the context of a photogrammetric evaluation, this means that the projector can be modeled as an inverse camera 
delivering 2D “image” coordinates. 
Our projector features a LCD with 640x640 lines, line spacing of 90 um and a halogen light source of 400W. 
According to the specification, patterns can be switched in 14 milliseconds making it feasible to acquire images in video 
real-time. Nevertheless, using high quality cameras, we found that the latency time to completely replace one pattern by 
another is about 50 ms . Commands and pattern sequences can be sent to the projector via a RS-232 interface. 
In our previous experiments, we used a standard video camera (SONY XC75) with a 1/2” imager and approximately 
8 um pixel size, grabbed with an ELTEC frame grabber at 748x576 pixels. This camera has been replaced by a pair 
of high quality, digital cameras (Basler A113) with 2/3” imagers, 6.7 um pixel size at 1300x1000 pixels and 12mm 
Schneider-Kreuznach lenses. 
Projector and camera were mounted on a stable aluminum profile with a fixed, but unknown, relative orientation 
(Figure 2). 
  
Figure 2. Hardware setup consisting of an ABW LCD 640 Cross stripe projector 
and two Basler A113 high resolution digital cameras. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 329