the procedure switches to the second lowest level, predicts, 
selects and matches the next image patch and again drops 
down to the lowest level, unless the end of the image patch 
of the third lowest level is reached. The path the procedure 
walks through the measurement tree circumscribes it follo- 
wing all branchings in full depth (cf. figure 3). 
The extreme case where the tree only has one level 
(except for the root) may be used for a pure manual measure- 
ment of the arcs, for testing the power of the prediction in 
dependency of window size, matching algorithm and point den- 
sity alone or for investigation the effect of the neighbou- 
ring level onto the quality of the prediction. 
3.2 On-Line Generation of Wire Model 
The wire model is generated by tying up the measured arcs 
to the already existing graph. At the beginning the graph 
contains only one node. There the measurement of the first 
arc starts. When reaching the end of the arc a new node is 
generated and added to the list of nodes. The just measured 
arc is put into the list of arcs and the arc description is 
saved. Now there are two "open" nodes where the arc measure- 
ment procedure could continue. The older one is worked out 
or "closed" first. If the end node of an arc is already in 
the list of arcs only the pointers are updated, the mea- 
surement, however, is not repeated. The arc measurement is 
continued until all generated nodes are closed, i. e. until 
there are no more free nodes to be able to start measuring 
at. 
There are various situations in which an arc is closed by 
its end node. If the currently measured arc crosses another 
intersection plane a new node has to be generated if it is 
not already existing. Also a new node has to be generated if 
the boundary of the area of interest is reached. The same 
holds if during the arc measurement procedure - for whatever 
reason - no more point measurements can be performed. In 
that case a node of degree 1 is generated. It may be reached 
from the other side lateron, increasing the degree to 2. If 
a surface edge is crossed the system should generate a node 
of degree 2 and continue measuring the arc until the next 
node. The edge must be added to the list of planes and be 
marked as being of type "edge". This last feature is not yet 
realized in the program. 
Following the described procedure the wire model is 
spreading over the surface in all directions away from the 
first node where the measurement procedure was started (cf. 
figure 4). Areas with poor texture automatically are circum- 
vented without stopping the measurement process as the 
system continues to measure the next open node. 
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