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tacheometric data 
Direct measurement of the terrain's surface usually is 
carried out by self recording tacheometric equipment. 
The objective in the field is, to use a minimum of 
reference points for the surface description. Addi- 
tionally planimetric objects (houses, roads, landscape 
elements) are measured. This points usually are added 
to the DTM primary data. The result are data sets with 
extremely inhomogeneous point distributions (figure 7), 
but a rather high point accuracy. 
digitized data 
If DTM primary data are gained from existing maps, 
contours are digitized with optional distance or time 
increments or manual recording. In addition to that 
special points (height coded points) and elements (lake 
border lines) are recorded. The characteristic of these 
data sets is a very high point density along the contour 
lines but a deficit of information between the contours. 
An automatic procedure is given by scanning contour 
folios. After the raster/vector conversion a data set is 
available with about the same characteristics the digi- 
tized contours show. 
3. DEMANDS FOR DTM PRIMARY DATA 
PREPROCESSING 
An approach for DTM primary data preprocessing 
should be able to check the input data set without any a 
priori knowledge. There are several demands which can 
be formulated from a practical point of view: 
- automatic determination of range in xyy and z 
- plausibility checks 
- information on point distribution within the project 
area 
- interactive procedure for gross error detection and 
correction 
- quality analysis of the input data set 
- special treatment of digitized contours 
- generation of reference points within defined areas 
(e.g. lakes) 
- generation of artificial reference points within areas 
of sparse or none reference point coverage 
- "on-line" check of the effect of the data manipulation 
- proposal for parameters of DTM interpolation 
  
  
For the user, it is of central importance that all tools are 
available within the DTM program environment. 
4. CONCEPTION FOR PRIMARY DATA 
PREPROCESSING 
An essential facilitation for DTM generation and also an 
improvement of the quality of the terrain description can 
be achieved by a preceding analysis and preparation of 
the primary data. Figure 1 shows a conception for pri- 
mary data preparation. The components of this toolbox 
are embedded in an interactive working process which 
enables fast 2D and 3D data analysis. 
  
  
  
  
    
      
    
  
  
  
     
   
primary data 
3 HE EET 
data base 
first check of the data 
  
  
visualization 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
gross error |::: T iii 
detection : P 
preliminary DTM 
(TIN) 
Skeleton lines 
from contours 
artificial points quality test 
within fixed areas products 
analysis of the point distribution n updated data 
mesh width for the final DTM 
  
  
  
  
  
  
  
  
  
  
Figure 1: Architecture for data preprocessing 
One part of such a toolbox is error detection and 
elimination. Also information about the terrain, 
embedded implicitly in the primary data, has to be made 
available for the final DTM generation. These 
information can be automatic derived skeleton lines 
when contours build the primary data set or points 
defining fixed areas (e.g. lakes) for the DTM surface 
description. 
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