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Potential of sunlight simulation to support conservation of Bayon archeological site Positioning 3D Model on 3D Globe Geometrical relationship among the Sun, object and its location on the Earth produces shadows. The 3D model of the Bayon produced in the previous section had to be placed at its precise location on a model of the Earth. Geo-coordinates to determine the position and orientation were derived from a field survey done in 1998 (JSA, 1999, pp145 - 151). This survey was carried out by using Real Time Kinematic GPS, and the position data set acquired was expected to have a high accuracy. Some of the geo-coordinates used for positioning and orientation of the 3D model in this study were as follows.
Variations in ground elevation among these four points were, according to the data set, within the range of 1m. Taking the "spatial resolution" of the 3D model into account, the ground on which the ruin was situated was approximated to a flatland. The landscape simulation software chosen for positioning of the 3D model and consequent simulations in this study used the normal sphere of which radius is 6,370,997m as the Earth model. The spherical model allowed positioning of the 3D model by using the latitude / longitude coordinates above. The changing movement of the Sun over a year was preset in the software, and it became possible to reproduce the condition of insolation and shadows over the site of Bayon at any given date and time of a year after the placement of the 3D model on the 3D globe. Simulations and Visualisations On the basis of the 3D model set at the position on the 3D globe, several experiments were conducted. They can be divided into two groups. One of those is the experiments for verification of the 3D model and its positioning, and the other is the experiments for inductive and deductive inferences to formulate a future conservation strategy. Comparison with Aerial Photograph To verify geometry of the 3D model itself as well as its relationship to the Earth and the Sun, a comparison was made between an aerial photograph taken from a camera installed on a blimp and a computer generated scene having the approximately same viewpoint. The aerial photograph was taken at 9:07 a.m. on March 12th, 1999 (Madhavan, 1999). The altitude of the blimp, hence, the camera was about 110m above the ground. In the landscape simulation software, the same lighting condition was reproduced, and a corresponding viewpoint was identified. As shown in figure 3, shapes and sizes of shadows are identical on the photograph and the computer generated image. This comparison also illustrates the degree of generalisation in the modeling process mentioned earlier.  Figure 3. Aerial photograph compared to simulated image Note: The white line on the aerial photograph is a captive rope of the blimp. |