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2.3 Digital image correlation: Automatic 3D point computation with InduSURF 
InduSURF has been developed by INPHO Stuttgart on behalf of and in cooperation with Carl Zeiss Jena. The computer 
platform is a Silicon Graphics workstation. The necessary transmission of the image and orientation data is performed 
via an Ethernet connection between the PC und SGI computer. The high transmission rate achieved even permits direct 
scanning from the PC to the SGI hard disk. 
InduSURF is based on the proven MATCH-T algorithms for automatic DTM generation using digital aerial photos, which 
have been extended by new measuring techniques and adapted to the specific requirements of close-range 
photogrammetry. The digital image data is processed by InduSURF model by model in the following cycle: 
1. Definition of internal control and output parameters of the program 
2. Interactive selection of the image areas to be plotted and normalization of these areas 
3. Generation of image and feature pyramids 
4. Computation of the 3D point coordinates 
  
  
  
  
  
  
  
  
  
  
stereo pair image pyramid feature pyramid 
point cluster breakline 
   
grid-type digital 
elevation model DEM “pyramid 
  
  
  
Fig. 3: InduSURF Digital - principle of image data processing 
The 3D point computation is performed by two methods: 
QO feature- based correlation of homologuous image points for the derivation of a dense point cluster of the surface, 
O least-squares correlation for the direct measurement of profiles and the generation of a wire frame model. 
Both methods ensure maximum reliability and accuracy in the plotting process. The accuracies achieved for the 
determination of points in the images in the bundle adjustment process are confirmed by the InduSURF measurement 
algorithms. The monitor offers on-line visualization options for checking the correlation. After computation of the data, 
the correlated image areas can be visualized off-line, with the accuracy ranges being displayed as overlays. In addition, 
the mean elevation error is output in the report. 
The image data can be processed by batch programs, i.e. image correlation can be run overnight, permitting full 24-hour 
utilization of the system. The CAD output either consists of the 3D point cluster (ASCII), the VDA format or DXF 
polylines. The processing time of InduSURF mainly depends on the 
O image data range (wide angle images) and number of images, 
Ql selected grid point distance for patches and profiles, 
C] power of the SGI machine (R4400 processor with 200 MHz is.prefered). 
IASPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995