Full text: XVIIIth Congress (Part B5)

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YAMMETRY 
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Once the images have been epi-polar re-sampled 
for display in stereo, observations were then 
made to all of the main construction elements of 
the structure in a manner so that they could be 
used to either create a surface or derive a ‘perfect’ 
element in the CAD system (in this case, 
MicroStation). This consisted of observing 
profiles along decorative surfaces that could be 
made into a surface of revolution, lines along the 
edge of surfaces that could be connected into 
regular or irregular shapes and so on. 
  
Figure 8: Buddha statue derived from a TIN model 
from photogrammetry. 
Other, more complex shapes like say Buddha 
statues, are observed as a non-uniformly spaced 
surface model with break-lines along the main 
surface features. Figure 8 gives an example of 
one statue, and shows one of the problems of 
modelling real-world surfaces in a CAD system. 
Investigations are in progress at the University 
into the use of other surface modelling routines 
to best display irregular surfaces of cultural 
monuments derived from the photogrammetric 
record. 
7. MODELLING CONSIDERATIONS 
Whilst the photogrammetry provides a 
convenient way of quantifying the architectural 
forms, and the historical documentation 
provides some of the attributes of these forms, 
considerably more is needed to make the 
visualisation succeed. Much of the other CAD 
models required are created within the CAD 
System wholly using the imagination of the 
Operator tempered by some geometrical 
Constraints. For example, the main Palace 
buildings have been created from a combination 
of the archaeological plan for the dimensions of 
the exterior walls, photographs of the model in 
423 
the Historical Research Centre, photographs of 
the half-scale recreation at the Ancient 
Thailand exhibition centre and photographs of 
suggested similar architectural styles. There is 
no building there to record, so the reconstruction 
is based on whatever material is at hand. A 
similar technique has also been used for other 
design elements like temple gongs and bells, 
oxen carts, gateways and so on. 
One source of information regarding the typical 
architectural decoration likely to have been used 
at Ayutthaya are photographs in Fine Arts and 
Crafts publications, and photographs acquired 
using conventional cameras at other locations 
in Thailand. A selection of these photographs 
have been scanned, and approximately scaled as 
an ‘ortho-image’. The MicroStation CAD 
software allows the display of raster images 
within the CAD package, allowing these ‘ortho- 
images’ to be used as a background so that 
intricate shapes can be traced from the pictures, 
and converted into complex CAD elements and 
hence into three dimensional shapes. This has 
been successfully applied to a selection of roof 
support brackets, windows and doors. These 
elements can be re-scaled to suit whatever 
building model they are being used to decorate. 
Photogrammetry is also being used to facilitate 
the modelling of an elephant for incorporation 
into the computer model, although a real 
elephant was not the subject of the study. A 
small elephant votive has been photographed in 
a control frame and observed stereoscopically. 
A surface model has been created from the data 
points, and re-scaled to what would be full size 
within the computer. It is intended to animate 
this model eventually, so that the trumpet of the 
King's elephants can be once again heard over 
Ayutthaya. 
8. THE VISUALISATION PROCESS 
The visualisation of landscapes and cityscapes 
is becoming increasingly common, especially in 
the areas of land use planning and 
environmental impact studies (Bishop, 1994). 
Generally, as a result of the scale being 
considered, they have been derived from aerial 
photogrammetry or satellite remote sensing. In 
the Ayutthaya Project, it was intended to use 
aerial photography as a data source but 
eventually this was not possible, so the 
modelling was performed from the terrestrial 
photography. The creation of the models has 
been undertaken using Intergraph/Bentley 
System's Micro- Station CAD package. It is a 
fully featured computer aided design package, 
and is fully integrated into the other Intergraph 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
 
	        
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