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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
shown in our model that the connectivity of the edges is
preserved when you modify the model. You can still *walk
through the hole".
The whole procedure of creating the hole satisfies the Euler
Poincaré formula and the topological validity is preserved. The
elementary Quad-Edge based Euler Operators are shown to be
able to generate and modify the traditional TIN structure,
permitting basic CAD operations (Tse & Gold, 2002).
New Edges
The edges
Face |
— — me a. on A Em WR Ee em
=o =f 2 =
,
-------Yy
New Edges
»
Fe C ou o ow EO we wm me
i
I
I
i
The edges
d
Figure 14 Second MEF splits the face
Besides creating holes and bridges, buildings are created with
connected topology on the terrain model. Fig 15 show two
simple buildings extruded from the terrain surface. In figs 12 to
14, we describe the procedures for creating a triangular tunnel;
the swap operator is used to enlarge the hole in fig 16. Swap
could be used to enlarge the bridges. Two bridges are created to
connect two complex buildings and two hills in figs 17 and 18
Separately.
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Figure 18 The extended TIN with two bridges
5. Implementation Using Real World Data
Part of Hong Kong is used to illustrate the extended TIN model.
A harbour area is chosen (Tsim Sha Tsui) in fig 19, with several
buildings, a bridge and a cross-harbour tunnel. Figs 20 and 21
show the result using the map data. The cross-harbour tunnel in
fig 22 connects between two sides of the harbour area. The
colourless area is formed by, the “underneath” triangles facing
towards to the user.
