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4.2 Fast Image Correlation
Potentially, the most time-consuming step in a DPW's bag of
tricks is the image match since a great number of correlation
coefficients have to be calculated and there is a lot of repeated
computation. To relieve this repetition, the necessary storage
space is retained for the calculated intermediate results. These
stored results can be used directly. Effectiveness will increase four
to ten times according to the size of the match window.
4.3 Fast Orthorectification
The normally time-consuming operation of orthorectification is
replaced by a simple add operation, therefore the repeated
calculation for the photographic coordinates of the DTM grid
points is avoided. The times of pixel input from disk to memory
is reduced to a minimum. The interpolation of the height
corresponding to each pixel on the orthoimage is replaced by
interpolations of photographic coordinates to avoid the time-
consuming calculation of collinear equations. Such a procedure
increases the speed by a factor two.
5 APPLICATIONS OF THE VIRTUOZO DPW
The dominant use of VirtuoZo is to create DTMs and Contoured
Orthoimages for mapping purposes, and as a data source for
proprietary Geographic Information System (GIS). Not only is
VirtuoZo one of the most exciting and innovative DPW available
today, it is also a superb visualisation tool. VirtuoZo has been
used on many projects, such as the colour stereo modelling and
orthoimage generation of the Three Gorges of the Yang Zi River
in China based on more than forty images (depicted in Figure 1);
the maps of the Loess Plateau area with scale 1:50,000 and a
height accuracy of 3.7 metres; the DTM and digital orthophoto
generation from panchromatic SPOT imagery with the 5-7 metre
accuracy in height; the solid modelling of individual objects in a
workshop or laboratory environment, explosive blast crater
measurement, management of land, the rapid DTM of Ayers Rock
in Australia (depicted in Figure 2); resource management;
dinosaur footprint archival and measurement from close range
images; architectural facade reconstruction; transport corridor
measurement; highway and railway design, etc.
Figure 2. Ayres Rock, Australia
429
The number of new applications is limited only to the imagination
of the user. According to the experiments of some users, the
accuracy of VirtuoZo is at least as good as some of the more
famous digital photogrammetric systems of the world, and
VirtuoZo has a speed advantage.
6. CONCLUSION
Research results of the theory and algorithms used in digital
photogrammetry support a practical and commercial DPW.
Already, DPW's are available and affordable. Their capabilities
allow them to produce all types of conventional photogrammetric
products, as well as some new products, such as stereo landscape
drapes. DPW can now offer the most exciting, innovative,
efficient, practical and cost effective photogrammetric solutions
available. Some of them are fast, reliable and dead-easy to use.
One of them is the VirtuoZo Digital Photogrammetry System.
REFERENCES
Wang Z., 1978. A Scheme on Developing a Fully Digital
Automatic Mapping System. Proceedings of the Symposium of
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Wang Z., 1995. From Photogrammetry to Geomatics -- A
Commmemoration of the Accomplishment That Is VirtuoZo. The
Official Newsletter of VirtuoZo System, Volume 2, Number 1.
Zhang J. and Wu X. 1993. Development of Digital
Photogrammetry in WTUSM. Geodetical Info Magazine (GIM),
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Zhang J., Zhang Z. and Wang Z, 1992. High Accurate Position on
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