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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
Figure 3. Comparing the reconstructions for the 2 conditions of 
the experiment in Sec. 3. Top 2 rows show the results for the 
Harris (left) and the SIFT (right) conditions, for two viewpoints 
(1 st row is top view and 2 nd row is side view). The last row of 
the figure shows a top view of the reconstruction of the same 
scene, from 35 views and the SIFT condition. 
4. VIRTUAL TOUR APPLICATION 
The reconstructed VRML models are integrated with GIS 
technologies within a Web-based virtual tour system, after 
converting them to the XML-based Collada 3D file format and 
then referencing to them in Keyhole Markup Language (KML), 
a format supported by the Google Earth™ GIS platform. 
Reconstructed part of the archaeological site is placed at its 
exact location on the terrain. Sample Google Earth™ views for 
Knossos (Greece) archaeological site are given in Figure 4. If 
the resolution of Google Earth™ at that location is not 
satisfactory, excavation site plan can be used as detailed raster 
overlay, draped over the terrain. Then the reconstructed 3D 
model will be seen on the site plan. 
We added a hyperlink to the application described above, which 
directs users to a panoramic image based virtual-tour. The main 
item in this a tour is a viewing window that the user can control. 
Using Java Applet technology is one proper way of creating 
such Web-based applications. In addition to the images, audio 
or textual information related to the site can be presented to the 
users with extra WWW tools. Using a map of the 
archaeological site increases the comprehension of the tour and 
enhances the user’s sense of orientation. A step further is 
making this site plan interactive and integrated with the viewing 
window. With such tools, more information is communicated to 
the virtual tour users in an ergonomic fashion (Bastanlar, 2007). 
Figure 4. Viewing models in Google Earth™. At the top, 
overall view of the site together with the reconstructed wall. 
Bottom-left is the close view of the 3D model of the 
reconstructed section. The image at bottom-right is a real 
photograph taken from archaeological site. 
In Figure 5, a screenshot of the virtual tour page is shown, 
which is implemented for the ancient settlement Selime Castle 
in Cappadocia, Turkey. At bottom-left the viewing window and 
at the right the site plan are located. The section of the site that 
is currently presented in the viewing window, field of view 
(FOV) and direction of view are indicated in the floor plan. It is 
updated accordingly as the user changes these controls. 
A larger degree of immersiveness can be experienced by 
viewing the reconstructed 3D models on autostereoscopic 
displays, which can be achieved by using a special plug-in, 
TriDef™ Visualizer for Google Earth™, to render real-time 3D 
scenes. We used this property to 3D render the scene for a 
stereoscopic notebook PC. 
The pilot application implemented so far can be reached at 
http://www.ii.metu.edu.tr/~3daegean/recent.htm 
5. CONCLUSIONS 
In this study, a Web-based virtual tour system is built for the 
presentation of cultural heritage. In the proposed approach, the 
scene is captured from multiple viewpoints utilizing off-the- 
shelf equipment. We developed and presented the techniques to 
extract the 3D structure from the acquired images based on 
stereoscopic techniques. For presentation and 3D modeling of 
outdoor cultural heritage, the proposed approach as a whole 
constitutes an economic and practical alternative to the 3D