International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004 
  
The user just needs to click on two points and the program 
calculates the distance between them. This fcature allows the 
user to perform data evaluation tasks in the field already. 
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Figure 4: The figure shows a 3D point cloud. 
Another feature is the semi-automatic target finder. [Abm04]: 
By clicking somewhere on a 10cm by 20 cm chess-pattern (see 
figure 5), the user gets the target centre with subpixel accuracy, 
and its corresponding 3D value respectively. This calculation 
needs to be precise and accurate, as this 3D information is the 
basis for calculating the orientation of each scan: For 
calculating the orientation itself for several scans bundle 
adjustment with standard tools is used. 
  
Figure 5: The figure shows the result of the target finder. Left: 
The target is taken with the high resolution mode 
(10000 pixel horizontally and vertically per 360° 
scan. in approx. Sm distance). Right: The target is 
taken with the preview mode (1250 pixel 
horizontally and vertically). 
LFM 
Light Form Modeller (LFM) has been developed specifically to 
convert 3D point clouds into 3D CAD models. A Conversion 
from point data to CAD objects is achieved by the application 
of analysis algorithms which have been generated to facilitate 
swift points-to-primitives translation. 
The modelling of small or large structures dictates that signifi- 
cant numbers of images need to be taken from a number of 
different viewpoints and consequently, building a 3D CAD 
model can quickly become a very complex undertaking. For this 
reason, LFM provides scamless support for the user to allow 
rapid registration of multiple images from several viewpoints in 
order to compose the 3D CAD model (see Figure 6). 
Model construction takes place on a hierarchical basis, that is to 
say objects can be constructed from smaller components and 
grouped to form an assembly. Once a complex object has been 
created it can be cloned or saved as a library component. Using 
a unique method of connectors, objects having these connectors 
can be simply snapped together to form larger groups of objects. 
This approach is particularly useful where a complex object 
appears in a model many times and the user needs to instantiate 
another instance of an object at a specific place. 
  
Figure 6: 3D CAD model of a chemical plant: The production 
facility has been surveyed from several different 
viewpoints. Targets have been used to match the 
scans together and to refer each scan to the local 
coordinate system of the facility. 
Conversion from 3D point data into CAD objects is facilitated 
by using a range of specifically generated fitting algorithms 
which have been developed to be both robust and accurate. It is 
an interactive conversion process, as the user selects specific 
groups of points and then directs the program to automatically 
find the best fit for a CAD representation of this object. This ap- 
proach leads to very swift construction of the model even for 
users new to the system. After carrying out an automatic 
segmentation, a semi-automatic fitting of pipes. planes and 
other primitives is possible with some interaction required. The 
LEM fitting algorithms are extremely robust to noise and 
outliers, so that they still work even if the quality of the points 
is not as high as usual, which may happen at certain very dark 
surfaces. 
Meshing is another method of processing the data obtained by 
the laser scanner. It is extremely useful for objects with complex 
and free form surfaces like statues or castles. Meshing takes the 
cloud of data points and produces a triangular mesh which 
closely approximates the surface formed by the cloud of points. 
These Point clouds can vary immensely in density, overall size 
and surface complexity, so thc meshing system has been 
designed to be able to deal with this on an automatic basis. 
LEM includes interfaces e.g. for AutoCAD 3D, Microstation SE 
& J, PDS (Geometry) through Microstation, PDMS (Geometry) 
through IMPLANT, CATIA, RobCAD, Polyworks, Laser Gen, 
Cloudworx and all other CAD systems which are open to 
Microstation and AutoCAD inputs. 
  
  
  
  
  
   
    
   
    
  
  
  
  
  
  
  
   
   
   
    
    
    
   
   
    
    
   
  
  
  
  
  
     
    
   
    
     
    
   
   
    
    
    
    
   
    
   
  
    
   
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