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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