; organi-
‚For the
polation
)73; Eb-
9 better
^n inter-
(figure
ng from
ical in-
yy local
o diffe-
rent data types this is called a HYBRID data struc-
ture (figure 4).
Figure 4: HYBRID data structure
Practical experience has shown that the user should have
the opportunity to choose one of the above mentioned
data structures, according to the requirements of the
project concerned.
3. DTM DATA STORAGE
The storage of DTM data can be organized by sequential
files, direct access files, and list structures in which
position and topology is maintained. Up to now less
importance was given to object thematics, however, this
is a postulate for a successful integration as explained
later on in more detail. An existing data model of a DTM
should be extended such that it should not be primarily
position oriented but to be topological and thematic as
well.
3.1. TIN data organization
As far as TIN is concerned different modes for data
storage may be used (Fritsch,1991):
- an organization with respect to triangles and
neighboring triangles
- anorganization with respect to edges
- anorganization with respect to edges and triangles
and complete maintainance of topology
499
The latter one is demonstrated by figure 5, in which
linear lists are used for position and topology.
nodes edges
node z y z edge nodes
201 1201 329 220 a 201, 202
202 1202 V202 2202 b 202, 203
203 1203 Y203 2203 C 201, 203
204 2204 Y204 2204 d 203, 204
205 1205 V2o5 2205 e 201, 204
211 zon Yan Zn f 203, 211
218 zns Yıs Z218 g 204, 211
221 z233 Van Zn h 204, 205
i 201, 205
J 211, 221
triangles k 204, 221
triangle edges l 205, 221
A a,b,c m 205, 218
B. rode n 201,218
C d,f,g
D e,h,i
E g.k
F h,k,l
I i,m,n
Figure 5: TIN data organization
3.2. GRID data organization
The advantage of a grid data structure is its simple
topology. The data is arranged like a matrix with rows
and columns describing planimetric data x,y; the matrix
elements are the z-values. For example, the grid of figure
6 is organized in a (3,4)-matrix. Because of its regular
topology grid data can be accessed directly. An impro-
vement of terrain description is mostly assured by extra
