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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