SPATIAL RECONSTRUCTION AND MODELING
OF THE SUNDAGGER SITE IN CHACO CANYON
Kurt Novak, Kenneth L. Edmundson, Phillip Johnson
Department of Geodetic Science and Surveying, Center for Mapping
The Ohio State University
Commission V
ABSTRACT
In Chaco Canyon, New Mexico, one of the most interesting astronomic observatories
used by native Americans was discovered more than a decade ago. It is known as the
Sundagger Site, and consists of three rocks which cast shadows onto a spiral carved into
the wall at the back of these slabs. At the summer-solstice these shadows form a
“dagger”, which moves exactly through the center of the spiral. It is also assumed that
this site was used as a lunar calendar, where the moon casts shadows on the same spiral.
During the past ten years, five different sets of photographic images of this site were
captured by different parties. However, they were never utilized to create a
comprehensive, 3-dimensional model of this observatory. In this paper, we report about
the integration of two of these photo-sets and the creation of a full 3-dimensional model
of the three slabs and its surroundings. We will discuss the problems encountered with
the old photographs, some of which have neither a metric calibration nor sufficient
control. The model of the Sundagger Site is visualized by a sophisticated surface
modeling program, which allows shading and ray tracing. Computer animation
techniques are then applied to simulate and study the casting of the shadows on the spiral
and their changes over time.
Keywords: Archeological, Close-range, Non-metric, Visualization
1. INTRODUCTION
Chaco Canyon is located in the northwestern corner of
New Mexico, which is an area rich in archaeological sites
dating back to 1000 AD. In this part of the USA there are a
large number of pueblos of the Anasazi Indians who
established a far reaching trade-network and built many
ceremonial buildings. To date nobody knows for sure why
this civilization vanished. As there are no written records
archaeologists have to rely on artifacts and ruins to solve
the mystery of the Anasazi.
Photogrammetric and geodetic techniques are of great
importance for creating data bases that can be used to
analyze the findings and establish connections between
related sites. The Anasazi pueblos have been studied for a
long time. Some were also surveyed and integrated in a
geographic data-base (GIS). One of the most interesting
results of these investigations was that all major buildings
of Chaco Canyon are aligned to either the cardinal
directions or to various positions of the solar or lunar
cycles. Although it is difficult to prove, archaeologists
assume that the Anasazi were experienced astronomers,
who did not only know about the precise motion of sun and
moon over the year but also utilized this knowledge for
creating calendars and observatories.
Probably the most interesting observatory is the
Sundagger Site. It consists of three slabs which are aligned
in front of a rock-wall on Fajada Butte in such a way that
they cast shadows onto a spiral carved into the wall (figure
1). At the summer-solstice these shadows form a sun-
dagger, which moves exactly through the center of the
spiral. It can also be shown that it serves as a lunar
calendar, where the moon casts shadows onto the same
spiral at its major and minor standstills.
Figure 1: The Sundagger Site consists of three rocks that
cast shadows onto a spiral.
Although these phenomena were directly observed at
the site, and could be empirically verified, archaeologists
want to be able to simulate these findings on a computer,
for the purposes of demonstration, education and archiving.
