290 
3.3 CNC milling: Digitization of models or sculptures 
In the industrial production. of components with free-form surfaces, a 3D data base is required for the manufacture of 
moulds and for the control of CNC milling machines for final shaping. The models and masters which are usually hand- 
made feature free-form surfaces, geometric objects which cannot be readily described in mathematical terms. Therefore 
these geometries have to be measured, and the data obtained is used to reconstruct the surface with the aid of CAD 
software. 
One market for this technique is, for example, the production of replicas on the basis of original sculptures. The 
measurement of such a sculpture with InduSURF has shown that digital photogrammetry is ideally suitable for creating a 
complete 3D data basis for an object, and that the added use of a digital plotter permits the incorporation of further 
valuable information into the plotting process. 
  
InduSURF Digital - Digitization of a Sculpture 
  
Task: Complete measurement of a sculpture approx. 50 cm in height, with maximum point density 
LC) DEM accuracy « + 0.2 mm with a 1 mm point grid 
CQ) Data output in the DXF format 
  
  
Parameters 
Sculpture - Recording and Plotting 
  
Sensor used 
Number of images 
Data quantity 
Defined points on the object 
Recording time 
Measurement and orientation 
Point accuracy 
UMK-SCAN, ck = 100 mm 
24 images (12 models) 
240 MBytes 
20 retro-targets on the object, 20 points on the object support 
30 minutes 
4 hours 
Sx/z 2 £0.23 mm, Sy2 + 0.19 mm 
  
InduSURF SGI computer 
Point number in DEM 
Computation time 
Mean elevation error 
  
  
Indigo, 100 MHz, 32 MB RAM 
280 000 points (1 mm grid) 
16 hours 
Sy = + 0.21 mm 
  
  
Table 4: 
Results of sculpture measurement 
  
Fig. 7: Sculpture, front view 
IASPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop “From Pixels to Sequences“, Zurich, March 22-24 1995 
Fig. 8: 3D point cluster of the sculpture