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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
  
Figure 8. General cutting cases 
Generally speaking, based on QTPV, the result of a plane 
cutting a 3D model is a profile. The follows show the processes 
of using a SP cut-away the model and formed a profile: 
(1) Initialize a stack S, and use S to store the identity of a 
QTPV intersected with the SP, initialize a queue Q, and use 
Q to store the triangles of the profile. 
(2) Get a QTPV from the Volume Element List (VEL) and 
evaluate whether it intersects with the SP. 
(3) If the QTPV does not intersect with the SP, a process mark 
is given to the QTPV in the VEL and the next QTPV 
without a process mark is the required to be found. When 
one QTPV is obtained, it is pushed into stack S. 
MÀ 
"s 
Pop a QTPV from stack S. Calculate the sub-polygon 
formed by the SP that intersects with the QTPV according 
to the topologic relationship among the QTPV geometrical 
elements. Partition the sub-polygon into triangles and input 
them into the queue Q. Give the QTPV a process mark in 
VEL. Find an adjacent QTPV that does not contain this 
mark and evaluate judge whether it intersects with the SP. 
If it does, then push it into stack S. 
en 
Repeat step 4 until stack S is empty and all of the QTPVs in 
the VEL are marked with the word “processed”. 
After the above processes a profile is formed and consisted of 
the triangles in the queue Q. 
5. QTPV MODEL APPLICATION IN STRATIGRAPHY 
AND SUBSURFACE ENGINEERING 
Based on the proposed QTPV model, the modeling methods and 
the model cutting process, we use VC++6.0 language, SQL 
database, and OpenGL graphic library under windows 
environment to implement a system prototype, named ‘3D 
Geological Modeling and Visualization (3DGeoMV) system’. 
The functions of this prototype includes: data input, data edition 
in 2D profiles, stratigraphy and laneway QTPV 3D modeling 
according to the borehole data and section data of laneway, 3D 
fence models of stratigraphy created by using different arbitrary 
planes cutting the model, visualization of all kinds of models 
and results, lamp-house control, model rotation and zoom. etc. 
Experimental data is composed of a set of real data of boreholes 
and a set of simulation data of laneway. The borehole data are 
from a geological exploration area in the Inner Mongolia, China. 
There are 42 original boreholes and 5 stratums. Since the 
stratigraphies are thin, for the purpose of increasing the viewing 
effects, the height values of boreholes are multiplied by a factor 
more than 1.0. Meanwhile, an interlayer is added so as to 
validate modeling function of 3DGeoMV. To obtain a smooth 
43 
stratigraphy model, an interpolation process has been done 
between two sparse boreholes in a profile by using curve fitting 
method. After interpolation 212 virtual (interpolation) and real 
boreholes are obtained in all. The  wire-frame graph 
representation of the stratigraphy model is illustrated in Figure 9. 
Visualization of 3D stratigraphy model is shown in Figure 10 
and the cut 3D stratigraphy model is shown in Figure 11. Figure 
12 shows 3D fence model of the stratigraphy model. Modelling 
results of a set of simulation laneway data are shown in Figure 
13. 
  
  
  
  
  
Figure 12. 3D fence model of stratigraphy model 
  
Figure 13. 3D model of laneway model