The coordinates of all surface points are available in a 
local coordinate system, which was oriented to north, east 
and vertical by geodetic measurements (astronomic 
azimuth). During our investigations we tried to simulate 
the light and shadow patterns created by the Sundagger 
Site: 
* the dagger moves through the center of the spiral at 
the summer solstice, 
* there are two daggers at the edges of the spiral at the 
spring and autumn equinoxes, 
* there is one dagger cutting through the small spiral 
at the winter solstice, 
* the moon casts a shadow at its major standstill 
exactly through the center of the spiral. 
6. CONCLUSIONS 
Archeo-astronomers assume that the Sundagger Site of 
Chaco Canyon, New Mexico served both as a solar and a 
lunar calendar for the Anasazi Indians. Its origin and use 
remain a mystery and a controversy in the archeological 
community. In this paper we described the successful 
creation of a 3-dimensional computer model of the site 
which can be used as a visualization tool both for education 
and experimentation. It might be useful for solving some 
of the mysteries of the Sundagger Site in the future. 
The surface model of the site was created by combining 
data from different, existing sets of metric photographs. It 
is represented as a 3-dimensional TIN in the computer. 
Visualization of the model is accomplished by applying 
surface modeling techniques, such as shading and ray- 
tracing. Computer animation was used to accurately 
recreate the shadows and light-patterns which are cast onto 
the spiral on the back-wall at various stages of the solar and 
lunar cycles. Additionally, the ability to perform 
transformations of the rock-slabs in the model permit to 
study how movements of the slabs may affect the light 
patterns. 
We are currently integrating the Sundagger Site model 
in a GIS of the whole Chaco Canyon area. This data-base 
will contain various pueblos located in and around the 
canyon. They are being scanned from existing drawings 
prepared by archaeologists. Their correct geographic 
locations are determined by GPS. This GIS will allow 
researchers to study the culture of the Anasazi Indians in a 
more comprehensive way; it will also permit to easily 
comprehend the spatial relationships between the buildings 
and their astronomic orientations. 
7. REFERENCES 
Sofaer A., Zinser V., Sinclair R., 1979. "A Unique Solar 
Marking Construct." Science 206, pp. 283-291. 
Sofaer A., Sinclair R., 1986. "Astronomical Markings at 
Three Sites on Fajada Butte". Astronomy and 
Ceremony in the Prehistoric Southwest, chapter 4, 
ed. J. Carlson and W.J. Judge: Albuquerque: 
Maxwell Museum Technical Series, University of 
New Mexico. 
     
8. ACKNOWLEDGMENT 
The authors want to express their thanks to Anna 
Sofaer, president of the Solstice Project, for supporting our 
participation in the reconstruction of the Sundagger Site. It 
was an exciting application of photogrammetry. We also 
thank Erich Brechner (Boeing, Computer Services) for 
making the source code of his shadow casting program 
available to us. The help of Aero-Metric, Inc., of 
Sheboygan Wisconsin is also appreciated; their 
reconstruction of the slabs was an invaluable data source 
for our model. Finally, we thank the Center for Mapping 
for allowing us to use their computer equipment.