or structure lines or the automatic exclusion of areas where 
measurements on the surface are not possible, not meaningful 
or not necessary. 
In a first step we, however, restrict to surfaces with a 
proper texture at all - or nearly all - places which are 
required and to a precise determination of the intersection 
of the surfaces with the given planes. Thus profiles or con- 
tours are directly to be measured by the system. This situa- 
tion might occur in industrial applications such as the 
determination of car body surfaces. 
The concept heavily relies on several conditions and 
requirements: 
1.) The human operator provides the system with starting 
conditions as well at the beginning as after possible 
break downs of the measurement procedure. 
2.) The measurement procedure is reliable in the sense 
that it either performs its task or gives a message 
that it can not perform it, possibly indicating rea- 
sons for the break down. 
3.) The data structure should allow to describe (nearly) 
arbitrary surfaces, should be able to be built up and 
updated during and after the measurement process and 
should allow to use different measuring strategies. 
4.) The measuring procedure should enable to easily 
change between different matching procedures,  espe- 
cially between human and automatic measurements and 
between precise (least squares matching) and fast 
(feature based matching) algorithms. This change may 
either be decided or indicated by the system, e. g. 
depending on the local situation on the surface or by 
the operator, e. g. for check purposes. 
The following sections want to describe the concept in 
detail. The structure of the problem (section 1) discusses 
the possibilities for measurement procedures and surface 
descriptions. The data structure (section 2) mainly consists 
of a wire model and a latent measuring tree. The on-line 
generation of the wire model, essentially a graph and the 
automatic measurement of its arcs is described in section 3. 
An example in section 4 wants to demonstrate the capabili- 
ties of the system. 
1. Problem Structur 
An automatic system for surface measurement needs an 
appropriate representation both for the surfaces in concern 
and for the measuring process. The choice of such a repre- 
sentation depends on considerations wich partly are indepen- 
dent on the particular realization but also have to take 
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