5. Experiment
Based on the current version of VirtuoZo,
the author has made a program on SGI
Indigo2, which we call WuTINOrtho. With
WuTINOrtho, we have produced the ortho
image of the Main Hall of the Chi Lin
Nunnery, which is one of the ten famous
scenes in Hongkong.
Shown in fig.4 are five photos of the Main
Hall, which is photographed by WILD P31
and scanned by Vexcel 3000. The scanning
resolution is 0.020mm. The principal
distance f is 9.66mm. Viewed from the front,
the visible width of the building is about 33
m, the height is about 17m, and the depth is
about 17m. The largest photographing
distance is about 27m, and the smallest
distance is 10m.
Table 1. The precision of inner orientation
| Precision\photo |
DX12 |
DX13 |
DX14 |
DX15 |
DX16 |
| Mx(mm) |
0.026 |
0.001 |
0.003 |
0.003 |
0.010 |
| My(mm) |
0.004 |
0.004 |
0.002 |
0.002 |
0.002 |
Table2 The precision of relative orientation
| Precision\model |
DX12-13 |
DX14-15 |
DX15-16 |
| Mq(mm) |
0.004 |
0.004 |
0.003 |
Table3 The precision of absolute orientation
| precision\model |
DX12-13 |
DX14-15 |
DX15-16 |
| Mx(cm) |
0.68 |
0.42 |
0.67 |
| My(cm) |
0.56 |
0.52 |
0.50 |
| Mz(cm) |
0.70 |
0.53 |
0.35 |
Fig.4 Five Photos of the Main Hall of Chi Lin Nunnery
Fig.5 pictures of incense burner and grades
Fig.6 Orthoimage of the Main Hall
After orientation, we measured the front
surfaces of the building with VirtuoZo
digitizing program. For some part such as
pillar and tiling, the data measured in filed
are adopted. In addition, some relative
constraints of the building itself are
included.
Left Part of fig.5 is the map of incense
burner and grades, the right part are their
orthoimage. Their scale is 1:50. On the
original images, the scale of the incense
burner is much larger than the scale of
grades, and the incense burner hides large
part of the grades. After ortho rectifying,
their scale is changed to 1:50. The hidden
part of the grades is resampled from other
images.
As for the blank area caused by the dead
angle of photographing, they are fixed with
Photoshop.
6.Conclusion
From this experiment, we can say, the
orthoimage making program WuTINOrtho,
which is based on the current version of
VirtuoZo digital photogrammetry system, is
practicable, the algorithm in which multiple
levels of TINs, hiding relation
reconstruction and context mapping
technique are included is feasible for close
building photogrammetry.
Making close range building orthoimage
requires multiple stereo models, accurate
orientation results and geometry data, high-resolution
images, and taking relative
constraints into account.
The digitizing of object surface is a key step,
which costs most time. For the ancient
building such as the Chi Lin Nunnery, the
image matching result is still unacceptable.
And the manual measurement of them is
also difficult. In the future, more research
should be focused on the automatic data
acquirement from the images of close
building, in which object model, context
pattern, relative conditions can be
considered.
Reference
- Wang Zhizhuo.Principles of
Photogrammetry with Remote Sensing.
Press of Wuhan Technical University of
Surveying and Mapping, 1990
- Zhang Zuxun, Zhang Jianqing, Digital
Photogrammetry.Press of Wuhan
Technical University of Surveying and
Mapping, 1997
- Jonathan Richard Shewchuk.Triangle:
Engineering a 2D Mesh Generator.
http://www.cs.cmu.edu/~quake/triangle.html
- 4. David F. Rogers, Procedural Elements
for Computer Graphics, McGraw-Hill,
Inc., 1983
