In many cases, it is beneficial for improving 
representation accuracy and reducing storage space. 
Also, Octree and TEN are two specialties of hybrid data 
structure. 
  
  
  
  
  
  
  
  
  
  
  
203 204 
Figure 3. Hybrid Data Structure 
Octree Tetrahedron Triangle 
  
  
  
Morton ATT || TEN Surfs ATT TN Segms ATT 
  
  
  
  
  
  
  
  
  
ya. JI A a,b,c 
73 SX - A; BCD B; b,d,e 
C. c,e.f 
D.a df 
Line Node 
  
LN Start End ATT PN 5X sY:52 nATFE 
  
a 43,2 4,42 201 X201 Y201 Z201 
b 202 4,42 202 X202 Y202 Z202 
C.4.3,2:: 202 203 X203 Y203 Z203 
d: 442 :3,4,2 
204 X204 Y204 Z204 
  
  
  
  
  
  
Table 4. Data Organization of Hybrid Data Structure 
Although hybrid data structure has some advantages in 
representing geo-objects, it should be appreciated 
properly. For instance, in geological modeling, while 
geology construction is regular and complete, Octree may 
be a suitable data structure; while geology construction 
is tattered and many faults included, TEN may get a 
better result; while a few faults are involved in geology 
construction which is complete, hybrid data structure is 
useful. Additionally, data structure selecting also depends 
on some other factors such as data type, object 
characteristic, spatial operation and analysis, etc. 
4. 3-D GIS BASED ON HYBRID DATA STRUCTURE 
4.1 A Concept of 3-D GIS 
A concept of 3-D GIS based on hybrid data structure is 
shown in Figure 4 depending on the discussion in front 
Sections. Five modules in this framework are User 
Interface, 3-D Modeling, Data Conversion, Spatial 
Operation and Relational Database. 
User Iterface 
3-D Modeling 
Octree, TEN, NURBS 
; 
Data Conversion 
Octree <== TEN Spatial 
TEN <==> NURBS 
NURBS <==> Octree 
i 
Relational Database 
Octree Data Attribute Data 
TENData + IC i 
NURBS Data Topology Data 
  
  
  
  
  
  
  
  
  
  
Operation 
  
  
  
  
  
Figure 4. Framework Of 3-D GIS 
Interactive user interface provides possibility of 
intercourse between user and system from it user can 
control system and get results. Three 3-D modeling 
methods in 3-D Modeling module are Octree, TEN and 
NURBS. Octree is a kind of raster structure which can be 
built from 3-D array that is formed by spatial interpolation 
of observations. TEN is vector structure which can be 
generated directly from dispersed observations. The 
combination of Octree and TEN is used to form hybrid 
data structure. NURBS is a parametric function also a 
vector structure which is erected from subsurface 
observations. Data conversions provide a link among 
different data structures and data which come from 
different resources can be uniformed in one structure. 
Also, lots spatial analysises can be carried out readily by 
selecting different data structures. Spatial operation 
provides all kinds of spatial manipulations and analysises 
such as 3-D visualization, geometric transformation , etc. 
Relational database is a useful tool in data management. 
After some extension spatial manipulation and query are 
carried out in relational database. Relational database is 
efficient for management of TEN data. When resolution is 
high, spatial index is needed for Octree data in relational 
database. Because parametric coordinates of NURBS 
are purely local and cannot serve as part of a primary 
spatial indexing for some spatial searches, relational 
database is not very suitable for NURBS data. In addition, 
topology data and attribute data are integrated in all kinds 
of data. 
506 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
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