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Case Studies

Laser Scanning Supports State-of-the-art Ancient Tomb Study

Laser Scanning Supports State-of-the-art Ancient Tomb Study

Introduction

On 26 November 2014, the Sanyo Shimbun newspaper in Japan published an article entitled ‘Discovery of a Rectangular Ancient Tomb’. Located in Soja, Okayama, and measuring 65m in length, the old tomb was named the Ancient Tomb of Mount Chausu. Earlier in the year a local resident first discovered what looked like an “ancient tomb”. Upon further investigation, it was confirmed that this was indeed one of the largest rectangular tombs within the prefecture.

Of late, Professor Izumi Niiro from the Archaeology Laboratory of Okayama University made a trip to study the ancient tomb. Using a laser scanner, the team performed a three-dimensional (3D) survey to create a detailed contour with the 3D point cloud data collected. Mr. Kenji Seki, the President of Seki Seko Kanri Jimusho (Seki Engineer Service) in Okayama City assisted Prof. Niiro in acquiring the data for this project. He used the FARO Laser Scanner Focus3D to conduct the 3D survey, and later used the InfiPoints software to process the large volume of point cloud data collected.

3D survey of the Kosako Otsuka Ancient Tomb

3D survey of the Kosako Otsuka Ancient Tomb. Pictured are Prof. Niiro (first from left) and Mr. Seki (second from left).
Photo courtesy of Okayama University Archaeology Laboratory.
 

Conventional Methods

Traditionally, an archaeologist would create a contour map of an ancient tomb by using the plane table surveying technique, where each point on a contour is observed and plotted on a drawing. While the method is still very much in use, it is time-consuming and the intervals between contour lines are wide. For an ancient tomb as large as the one at Mount Chausu, the task of plotting every single point would take close to a month. Besides, the concern of overlooking details was a real one, given that information between contour lines would be unavailable and that the narrowest possible gap between contour lines would still be a significant 20cm.
 

3D Survey of Ancient Tombs Using State-of-the-art Laser Scanning Technology

The first survey that Mr. Seki carried out with Prof. Niiro was for the Tsukura ancient tomb in Okayama Prefecture. For the project, the duo used a Total Station to survey the contour, and a laser scanner for the 3D survey. They realized then that the 3D survey was able to capture information that had gone undetected when they used the conventional plan table surveying technique. Laser scanning facilitates the creation of contours in centimeter intervals, which allows the team to visualize the inclination of the ancient tomb down to the smallest detail. With this new information, they noticed that ancient tombs were very accurately created in stages. While conversion points between construction stages were ‘hidden’ or indiscernible when viewed at ‘low resolutions’ of 25cm contour intervals, these were well visualized with the 3D laser scanning technique. This difference clearly demonstrates the effectiveness of using 3D survey for ancient tomb research.

A contour map with 20 cm contour intervals

3D point cloud data of the Mt. Chausu Ancient Tomb on the InfiPoints software, with data points of trees removed.

A complete contour map

A contour map with 20 cm contour intervals, as created by Mr. Seki.

Contour map

A complete contour map, where traces of tomb raiding and soil erosion (due to digging) can be clearly seen at the rear of the tomb.

According to Prof. Niiro’s research, ancient tombs were created in three stages and had utilized measurements that originated from China. It was found that this tomb was inclined at just the right angle, so that it would not collapse. Moreover, it was apparent that the various circular and rectangular sections were intentionally meant to control the tilt. Prof. Niiro said, “By analyzing the scans in detail, we can understand how the ancient tombs were created and were able to present the design principles behind them. Up until today, we had thought that ancient tombs were merely two-dimensional planes. However, scanning has finally proven that they are after all three-dimensional structures, of flat surfaces and elevation.”

As the team continued with their analysis, they further realized that the embankments in ancient tombs were created using construction techniques that are almost identical to present day methods. Amazed by how advanced technology had been back then, Prof. Niiro commented, “I think they probably memorized the methods since there were no design drawings back then. While it may have been complicated, people must have created the tombs based on principles they had memorized. Even now, embankments are made with the same incline as that of ancient tombs. The wisdom that ancient civilization possessed is truly astonishing.”
 

Future Applications of 3D Data

Having scanned five ancient tombs with Prof. Niiro, Mr. Seki readily highlighted the benefits of using the Focus3D for such projects. He revealed, “Some of the device’s advantages are its compact nature and portability, which enables it to be set up anywhere. The ability to deploy it easily means that survey time is drastically reduced. Even if a grave has to be destroyed, the Focus3D can be used to scan and digitize the site for archival first. Prof. Niiro is at the forefront of the research in that regard.”

Expounding on the idea of actively using the Focus3D for surveying of public infrastructures, he added, “Since the Focus3D can scan large structures in a short time, we have managed to scan large-scale public facilities such as dams. If we can incorporate public coordinates into our scans, it would add tremendous value to our survey data.”

Scanning of the Aguraguchi Dam that is mid-stream of the Nakagawa River in Tokushima Prefecture

Scanning of the Aguraguchi Dam that is mid-stream of the Nakagawa River in Tokushima Prefecture. A small and lightweight device, the Focus3D can be easily set up even in areas with rugged terrain.

Prof. Niiro said, “Now that we understand the design principle behind a typical ancient tomb, we are going to apply that knowledge to smaller ancient tombs so as to decipher how they were created back then. When I present the results from my analysis of a famous ancient tomb, I expect a sharp increase in awareness for this subject matter. I think 3D data will continue to be widely utilized in ancient tomb analysis.”

Looking ahead, Prof. Niiro anticipates embarking on more projects to digitize archaeological finds with Mr. Seki. He also hopes to work with 3D information in the research of ancient tiles, which to-date has only been studied with rubbing techniques to obtain 2D impressions.

Bird’s eye view of an ancient tomb created with 3D data

Bird’s eye view of an ancient tomb created with 3D data.
 

About Department of Archaeology, Okayama University

Staffed by 3 lecturers, the department consists approximately 25 undergraduates and postgraduates. The archaeological exhibit room displays information of archaeological finds from various regions in Japan, including Okayama Prefecture. The students enjoy a research-conducive environment, where resources such as computers and literature are readily available. Prof. Niiro’s research interests are focused on the excavation of relics and remains of ancient tombs in Japan, through the use of computer archaeology techniques to elucidate social dynamics and characteristics.

For more information, please visit www.okayama-u.ac.jp/user/arch/index.html.

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