ones exactly. The high quality of the surface description 
is represented by the intermediate contours (thin lines 
in fig.3). Artificial terraces are avoided completely. 
Moreover, irregularly distributed contour lines do not 
cause any problems. The shaded relief representation 
shown in fig. 4 demonstrates, that the TIN-DTM is of 
high fidelity but not smoothed. 
The data organisation of a TIN based DTM is rather 
complicated, especially if countrywide DTMs have to be 
generated. 
  
       
  
  
3.2 "Simple" grid-DTM 
An essential advantage of a grid-DTM in contrast to a 
TIN-DTM is the simple data organisation, especially for 
large DTMs. The grid-DTM is well suited for data man- 
agement within a data base and allows for quick data 
access. 
To combine the advantages of both the TIN-DTM and 
the grid-DTM, a "simple" grid-DTM is generated by 
interpolating the DTM grid points directly from the TIN. 
The contour lines derived from such a "simple" grid- 
DTM are shown in fig. 5. They are nearly the same as the 
  
: Fig. 6a: Sha 
ones, derived from the TIN-DTM (fig. 3). The "simple" othed "s 
grid-DTM allows the reconstruction of the original con- 
tours nearly exactly. Artificial terraces are avoided and lines are 
problems because of irregularly distributed reference dined abe 
data do not occur. The TIN, which is needed for the 
: i K ; 2 problems c 
interpolation, can be calculated in subareas with suitable 
ans grid points 
ovenaps: can be usec 
1992). 
To minimi: 
smoothing 
| í finite elem: 
e | => e ZZ grid-DTM 
EUN. \ I ^ ^ ZZ by shaded r 
7 : pulpa S i id both meth 
Fig.3: Contour lines derived from a TIN-DTM. The thin | 
smoothed 
lines represent the intermediate contours. 
  
  
  
attractive a 
The skeletc 
shown in cl 
logical infor 
odsshowni 
DTM. The 
Fig. 5: Contour lines derived from a "simple" grid-DTM. leads to thé 
The thin lines represent the intermediate contours. is less iisefu 
cated data 
3.2) is gene 
3.3 Smoothed grid-DTM directly froi 
: able with th 
| Generating a smoothed grid-DTM by means of finite [initc/zlem 
Fig. 4: Shaded relief representation derived from a TIN- elements has proven to be very suitable (Ebner/Rei, smoothed 
DTM. 1978; Reif}, 1986). A high fidelity smoothed DTM can be generated. 
generated, if the contours and the additional skeleton 
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