302 
  
CCD - camera 
  
beam- reflector 
N 
levelling rod 
  
  
  
  
  
  
(^y $— trolley 
gl? 
motor > 
  
bench 
  
  
astra aem ges 
  
    
  
  
  
  
— 
486 PC for control, 
| | data acquisition 
| 
| 
and processing Meissl 2.95 j 
Fig. 2 Automated rod calibration at the IGP 
  
  
  
3. THE DATA-ACQUISITION AND CONTROL SOFTWARE 
The software has been developed in Turbp Pascal and performs under MS-DOS. Its three tasks are: 
3.1. Control the course of calibration and support the operator 
The program presents a menu to the operator and guides him through the process of system preparation and 
calibration. 
3.2. Data acquisition and motor-control 
Communication with the laser-interferometer and the CCD-camera is via plug in data-acquisition-boards supplied with 
these instruments. The software that comes with the interferometer delivers ready-to-use distance information. The 
software for the CCD-camera delivers 8-bit grey-values for each pixel. Parts of the visualisation-software for the CCD- 
camera have been implanted too. 
For motor control the serial interface is used. There is no need for high positioning accuracy, it is only necessary to 
position the edges of the scale marks roughly at the centre of the CCD's field of vision. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995