The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008
650
ranks above. During the experiment it has separately done the
simplification in three ways under the single condition and got
three different simplified models of their own effects. These
three simplifying strategies have some diversity in both
simplifying effect (Figure 5) and efficiency (Table 2), which
give an opportunity for realizing personality to the clients and
own a good flexibility.
(a) (b) (c)
Figure 5. The effect of 3 simplification strategies
\name
stair\
Latency
triangle
number
simplified
triangle
number
Simplified
rate
(%)
remark
First
stair
97,266
11,074
11.39
only for the
triangles of
heavy
Second
stair
97,266
27,522
28.30
for heavy
and
moderate
Third
stair
97,266
46,296
47.60
for ail
Table 2. The comparison for different strategies’ efficiency
The experiment indicates that:
• In the aspect of simplification effect, the model
simplification driven by perception can well keep the
surface characters of the components, which ensures the
consistency on the surface of the whole building before and
after the simplification.
• In the aspect of efficiency, together with the effort of
simplification threshold value, the simplification operation
driven by perception has sharply cut down the whole model
data amount, and the model simplified rate is ranging from
10% to 50% according to different simplification strategies.
• For the LOD model of the highest level which needs to be
built, it can sharply reduce the model’s data volume;
meanwhile well keep the shape of the whole model.
• Those three kinds of simplifying strategies in the process
offer many choices to the clients, and they can flexibly
choose a suitable way according to their hardware and soft
ware conditions and their grasps to the granularities for
model representing.
6. CONCLUSION
In currently, complex building models are widely used in
various fields, such as VGEs, cyber city, and culture heritage
documentation, with well development of the virtual reality and
3DGIS technologies. But such high complexity and huge data
volume of building models can not meet the real-time and
interactive application requirements in virtual environments.
Perception-driven simplification in this paper is founded on the
image process that rendered image of building models are
filtered by HVS filter based on wavelet transformation. The
perceptual information is acquired and passed to model surface
by ray casting through finding the difference between rendered
image and filtered image. The model surface’s perceptual
information drives simplification operation directly to reduce
the imperceptible details on model surface.
A prototype is developed to create multiple levels of building
models. The simplification experiment of a complex ancient
building model proves that the simplified models not only
preserve the perceptually details of the model, but also
minimize the amount of triangles and keep high geometric
fidelity.
REFERENCES
Butler, D., 2006. Virtual Globes: The Web-wide World. Nature,
439(2), pp. 776-778.
Coors, V., 2001. Feature-preserving Simplification in Web-
based 3D-GIS. In: Proceedings of First International
Symposium on Smart Graphics, New York, USA.
Forberg, A., 2004. Generalization of 3D Building Data Based
on a Scale-Spaces Approach. In: International Archives of the
Photogrammetry, Remote Sensing and Spatial Inforamtion
Science, Vol.XXXV, pp. 194-199.
Forberg, A., 2007. Generalization of 3D Building Data Based
on a Scale-Spaces Approach. ISPRS Journal of
Photogrammetry and Remote Sensing, 62(2), pp. 104-111.
Forberg, A. and Mayer, H., 2002. Generalization of 3D
Building Data Based on a Scale-Spaces Approach. In:
Proceedings of the ISPRS Technical Commission IV Symposium
2002 on Geospatial Theory, Processing and Applications,
Ottawa, Canada, Vol.IAPRS, XXXIV, part 4, 6p.
Kada, M., 2002. Automatic Generalisation of 3D Building
Models. In: Proceedings of the ISPRS Technical Commission IV
Symposium 2002 on Geospatial Theory, Processing and
Applications, Ottawa, Canada, Vol.34, 6p.
Kada, M., 2007. A Contribution to 3D Generalization. In: 51st
Photogrammetric Week, Stuttgart, Germany, pp. 41-51.
Kobbelt, L., Campagna, S. and Seidel, H., 1998. A General
Framework for Mesh Decimation. In: Proceedings of the 24th
Conference on Graphics Interface (GI-98), Vancouver, Canada,
pp. 43-50.
Mannos, J.L. and Sakrison, D.J., 1974. The Effects of a Visual
Fidelity Criterion on the Encoding of Images. IEEE
Transactions on Information Theory, 20(4), pp. 525-535.
Meng, F. and Zha, H., 2004. An Easy Viewer for Out-of-Core