point of the vertical lines, is known in the image, the system is 
able to use this information for choosing the correct solution. 
Fig. 10 finally represents the result for interpreting the line 
drawing of the toy block in Fig. 3b, showing that the input data 
for the reasoning process need not to be a complete line 
drawing. 
  
  
Fig. ] 
a. 
5D 
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4 / / 
C / / For : 
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| Cl AES / proc 
| b. nal made The 
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| Fig. 8 Building à 
| well. 
| a. Orthogonal Sketch Ana 
| b. Representation of the building in space may 
| actu: 
| plan 
| clim: 
| ona nf : Ani 
| In case an orthogonal sketch is given (Fig. 8a), the operator is 
; ma 
1 asked to provide information about a trihedral corner. This y 
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starting rule is sufficient for the reconstruction of this building b. | 
are a 
in space (Fig.8b). The problem of the trihedral corner can only : ea 
i 
be solved if the two neighbour legs of one leg of the trihedral m ii 
corner are situated in two different quadrants (SUGIHARA e 
1986). Especially sketches, being manually drawn, and parts of me 
aerial images nearby the image border can be regarded as an gos Ma Ea ens 
orthogonal projection, not fullfilling this criteria. The system Spe 
; ; E comp 
then is able to automatically correct the position of the S 
t 
principle point in the image in order to determine the direction m er 
vectors of the three lines in space. T 
Fig. 9b represents an orthogonal sketch of a single house being € um 
andt 
derived from a part of an aerial image. As the exterior and 
interior orientation of the input image in Fig. 9a is given, the 
input data can be corrected with the coordinates of the 6 Lit 
it 
principle point, before the reasoning starts. Again only by Fig. 9 House 
indicating a trihedral corner at the object, the operator gets the a. Aerial image BAR 
reconstructed house in space (Fig. 9c). Here the supply of b. Sketch derived from a part of an aerial image Tech 
information is even reduced to the indication of a trihedral BECI 
corner. In case of the position of the nadir point, the vanishing c. Result of the reasoning process 
520