It's 12:30 a.m., and I'm watching a tiny green laser trace the outline of an 800-year-old Mayan pyramid—up and down, up and down. We have already been on site scanning for a couple of hours and have a couple of more to go. It's our first night shift of the project, and it has already been quite eventful. The night started with a sudden need to perform electrical triage on the power cable when frayed wires around the connection socket detached. Using a Leatherman and a headlamp, we spliced the wires and attached a new socket to the cord, giving us the power we needed for the scanner.

Once the scanner was up and running, we experienced how difficult it can be to locate targets by moonlight. Using a combination of course scans and flashlights, we tied our scanner into our control. Now everything is going smoothly. The scanner is working away, collecting millions of points, and we are free to take in the beauty of the site at midnight.

Even in darkness, the pyramid cuts an impressive shape. It rises above the flat plain and dominates other nearby temples. The site is incredibly still and peaceful, a complete 180 degrees from what it's like at noon, when tourists from Cancun arrive to take in the famous pyramid. But now it's just our team, the scanner, and the impressive monuments rising into the clear, expansive sky. As I look up, I am reminded that the night sky is what really brought our team to this site, Chitzén Itza. These great monuments now being traced by the laser were built by the Maya to aid in their study of the sky, and these great structures formed the reason for CyArk's trip to the Yucatan in eastern Mexico.

The Maya civilization constructed numerous cities and temples across the Yucatan peninsula, but the former urban metropolis of Chitzén Itza stands out as an archaeological site. Its recent designation as one of the New Seven Wonders of the World further emphasizes its importance in the Yucatan and its place in the world's cultural heritage.

At its height, the Mayan civilization stretched across parts of modern day Mexico, Belize, Honduras, El Salvador, and Guatemala. The Maya were some of the most creative and knowledgeable of the pre-Columbian New World builders. These architects of the emerging western hemisphere constructed large-scale urban centers with structures hundreds of feet tall. Many of Chitzén Itza's structures still stand today as a testament to the Maya's engineering skills.

Although Chitzén Itza is best known for the imposing step Pyramid of Kukulcan, other structures throughout this ancient cosmopolitan city hold equal fascination. The ball court is the largest in the Mayan world, stretching almost one and a half times the length of a modern football field. El Caracol, also known as the observatory, is one of the most interesting structures because of its astrological alignments. The Mayan's mathematical, astronomical, and architectural knowledge allowed them to construct this observatory to track the changes in the night sky. The Maya precision in tracking the stars drew our team and precision instruments to Mexico.

Planetarium Show to Result
The survey of Chichén Itza actually came out of a larger project that required detailed data of the Mayan ruins and their astronomical alignment. The Maya Skies Project is a project of the Oakland, California-based Chabot Space and Science Center in conjunction with Insight Digital and ARTSLab. The project was funded through a grant from the National Science Foundation. The finished product will be a full-dome planetarium show about the Maya and their astronomy. To create realistic and accurate models, the Maya Skies Project called on CyArk for high-definition documentation of one of Mexico's most popular archaeological sites.

Based in Orinda, California, CyArk is a non-profit organization that uses precise laser documentation to save historic and archaeological sites. As part of our documentation method, we use a Leica Geosystems High Definition Survey laser scanner, the instrument invented by the founder of CyArk, Ben Kacyra. We brought this machine to Mexico with the goal of creating a modern day record of this ancient structure. With its incredible precision and accuracy, the laser scanner is the perfect instrument to document the structural remains of a culture equally advanced for its time.

For this project, CyArk called on its partners in Michigan for help. Metco Services, a CyArk partner, specializes in consulting, engineering, architecture, and surveying and offers laser scanning in a variety of industries and sectors including automotive, manufacturing, construction, education, architectural, petrochemical, and public works. With CyArk's heritage focus and Metco's wide range of surveying expertise, our team was the right mix to take on a project with its share of heritage and surveying challenges.

The potential roadblocks to working on an international heritage site started long before the surveying with the fun of getting permits to work onsite and the logistical dice roll of moving equipment into the country. The uniqueness of work at a heritage site forced our team to think creatively throughout the project, addressing many questions. How do you find your control targets with hundreds of tourists in the way? If you need to use the rental car to power the scanner, how do you ask the local ferreteria (hardware store) if they have an inverter big enough? What is the best way to avoid the wild, territorial dogs on site?

Our team did what it took to get the job done. We worked shifts in the early morning and through the night to avoid the tourists and get a clean data set. We powered the scanner with every available source, from onsite electricity used for a light show to an outlet in the tourist snack shack. For the more remote parts of the site, the scanner was powered by the rental van and an inverter obtained with help from a local archaeologist. And for defense against the wild dogs, well, I'm not sure we brought enough. We made do with flashlights, tripods, and big sticks, but there were some pretty anxious moments.

Control Network Comes First
Our team was tasked with documenting six of the ancient structures dotting the site. To do so effectively, we first needed to establish our control network for the site. The extreme size of the project area, about a quarter by half mile, and thousands of daily tourists provided one of the biggest challenges we encountered. To minimize the impact of our team on the heavy vegetation and natural beauty found throughout the area, we decided the numerous footpaths winding throughout the jungle would act as our site lines.

The first workday on site was dedicated to surveying a control network that would encompass the areas of interest. Even when sticking to the footpaths, the difficult visibility made us grateful for our bright orange work vests. A closed traverse encompassing each of the six structures was completed, with 20 primary control points included. The overall angular error of closure was five seconds with an accuracy of 1/32000.

With the site-wide traverse completed, we could treat each structure as its own job site. This allowed for a greater flexibility in our documentation schedule. When needed, we could jump from one structure to the next to avoid interference from tourists or stay out of way of local archaeologists.

The most complex structure on site was also the most important for us to capture. We spent the majority of our time on El Caracol, totaling 37 scans. This consists of a large, square platform topped by a smaller square platform topped by a taller cylindrical structure. The observatory of Chichén Itza, El Caracol's name actually translates to "the snail." The Spanish gave it this name because of the concentric circles that form the top structure and its interior spiral staircase. These structural complexities made it difficult to document.

The top, cylindrical portion of El Caracol consists of three concentric circular walls. Not only is the space between the walls limited—sometimes less than three feet—the doorways between the walls are offset from one another. This meant careful planning for both scan locations and target placement. Paper targets were placed on the inside of the doorways to preserve a line of sight to the control points that had been set around the structure. The inside walls were also plastered with paper targets so each separate set-up could share as many common targets as possible. With our careful planning, we were able to successfully register all the scans together.

The scanning of the lower platforms of the structure was much simpler, and the three portions of the structure were easily registered. When looking at the scan data in the field, I first became concerned at the irregularity of the smaller platform. Not only was it not square, it was several degrees out of alignment with the larger platform. Having heard so much about the Mayan mathematic and architectural accuracy, I couldn't believe what I saw. Do we trust our control network or the Mayan architects?

Only after showing the scan data to an archaeologist did I realize that both were right, as the Maya had intended to build it that way. The supposed misalignment with the lower platform was actually a perfect alignment with the path of Venus. The elongated corners of the squares actually align with the summer and winter solstices. These differences are hard to notice with the naked eye but become clear by looking at the scan data. Not only was I relieved that our control network was not compromised, I was again amazed at the precision and planning that went into the Mayan structures.

Many Pleasant Surprises
For every challenge we faced in the field, there came a great surprise, like that one that seemed to make it all worthwhile: watching the faces of the local archaeologists light up as we showed them their site like they had never seen it before. They know every stone on the site, but flying over the structures and spinning them in three dimensions amazed them.

The pains of having to lug the heavy equipment to the top of several of the structures meant we got access to parts of the site no longer open to the public. Looking out from the top of the Pyramid of Kukulcan, the entire site was breathtaking. Jungle stretches as far as the eye can see, with the tops of the white limestone structures peeking out of the sea of green.

Another pleasure came in interacting with the local citizens on a daily basis, people who identified themselves as Mayan and speak Spanish as their second language to their native Yucatec. Everyone was curious about what we were doing and loved to talk about their ancestors and the structures they built. Our team even got to participate in a Mayan Moon Blessing ceremony. The ceremony has been practiced continuously for over 1,000 years and took place outside under the full moon. The entire ceremony was in Yucatec and proved a moving experience.

Despite the presence of the wild dogs, the late night and predawn working shifts made for some of the best times on site. We got to experience the site the way the Maya intended it to look. The sunrise threw dramatic shadows of perfectly aligned buildings across the open spaces of the site. The night shifts at El Caracol allowed us to actually view the stars from the Mayan observatory. Scenic beauty prevailed everywhere, and these quiet times on site gave us a chance to appreciate it.

We spent a great deal of time on site, and some of the best experiences had nothing to do with documenting it. But even with all those experiences to compete with, I was particularly affected by the documentation we did at night. There is something special about seeing the laser interact with the structures on the site—the contrast of the bright green against the dark night, the interplay between the new technology and the ancient stones, and the quiet collection of millions of points. Sitting there in the dark, I couldn't help noticing the irony of needing the latest technology to document something the Maya built entirely by hand.

About the Authors
Elizabeth Lee is manager of documentation projects at Cy- Ark. She has conducted fieldwork at Neolithic sites in Turkey and Hungary and at Incan sites in Peru, in addition to her most recent work at Mesa Verde National Park in Colorado and Chichén Itza in Mexico. At the University of California at Berkeley, Ms. Lee founded the UC Berkeley/CyArk Visualization Lab and served as instructor for the UC Berkeley/CyArk Internship Program. She has also conducted HDD training workshops for the U.S. National Park Service, the Presidio Trust, US/ICOMOS, and the University of Notre Dame. Ms. Lee holds a degree in anthropology from the University of California at Berkeley.

John Brown is the CAD/HDS project manager for Metco Services, headquartered in Detroit, Michigan. He has worked in the land surveying field since 1988 and has been with Metco Services since 1993. Brown has worked on such diverse scanning projects as Generals Motors plants, Mayan ruins, Easter Island, and the Three Mile Island nuclear reactor. He has helped create the workflow process for topographic surveys used by land surveyors.