SUM OVD and thus for constituting triangles as well can where contours serve as primary data only, though
101
yia then easily be realized (cf. Tang, 1991). various approaches beside a triangulation can be used
S for terrain modelling (Clarke et al., 1982; Christensen,
47 1987; Ebner/Tang, 1989; Aumann et al, 1990; Tang,
1991).
3.8
1011
1314
1617 . T
1920 The regions where the dashed lines appear can be
ms (aj {ai tes (d) (e) referred to as critical regions. They mark, however,
141
1112 the places where certain geomorphological elements
911 exist, too (cf. Figure 6). The geomorphological ele-
Figure 3. Possible fa V i in th : : T
es S oss cases of a; Voronol node in the ments here mean peaks, pits, saddle points, ridge and
QVD. : : : : :
710 drainage lines, which are essential for generation of a
811 . .
ers HQ-DTM from contours. In principle, they can be
1415
1718 0 1
2021 Figure 4. The N3-operator
2224 . .
12124 312 for locating a Voronoi
2225 node in the QVD.
02326
12427
s Examples for demonstrating the efficiency of the ras-
ter-based triangulation will be given in section 4.
3. DERIVATION OF GEOMORPHOLOGICAL
ELEMENTS FROM CONTOURS
To answer the question (2) in section 1 an approach
for automatically deriving geomorphological elements
xs from contours was developped and will be described
in the following.
3.1. Basic id
1-
Looking at the Figure 5, one can find out that the E
dashed lines are horizontal triangular edges which do
lead to an incorrect description of the terrain surface. Figure 6. Geomorphological structures reflected by
fol- As a matter of fact, it is hardly to gain a satisfactory contours.
rt result for the terrain surface description in this case
ore,
can
212
22
22
2:2
22 n V
SQ
MESSER UNS CASE
"Av, 7 RL 3 2S
GE AZ
OTSA VAI o ER
UL PSPDIRSENP NIS Sees AP
LT A VASE OS Ze D DIVA
= INSEE IE
the CAPAS RN SERRA
Ll NV De SISSE SENS
cif VANS AS SUI SS E EDO
jixels NS VV YA S ESTETICA A
ic ín: NANNIES RSG
nag Figure 5. A TIN constructed from contours. Figure 7. Medial axes of contours.
569
