The FARO ScanArm is used to scan another cultural relic in the Qingzhou Museum Project.
When admiring historical sites of meticulously carved grottoes, pagodas, and temples, or a monument scattered with stone steles and statues, what one may not realize is the fact that, regardless of location, all the beauty is quietly, slowly, and irreversibly being worn away by the environment. It is not obvious to the naked eye, but the same goes even for any collection of historical artifacts placed in the utmost care of a museum. And this is a hard truth that archaeologists and conservationists must come to terms with –– that these cultural treasures of surpassing value continue to age with the passage of time.
In the past, digitization techniques for cultural relic archaeology was considered icing on the cake. Today, however, it has become an essential part of an archaeologist’s foundational work process, as well as an important means of information retention. The digitization of cultural relics has enabled mankind to accurately record an artifact, in order to pass that information – as well as the historical, cultural, and technological value of an item – on to future generations in the permanent form of data.
The Cultural Heritage Research Institute of Zhejiang University in China was established on March 12, 2010. Since its inception, the institute has made outstanding achievements in areas such as digital archaeology, geophysical archaeology, and the research and application of cultural relic protection materials. In 2016, it received approval from the Government to set up the State Cultural Relics Bureau’s Key Scientific Research Base (Zhejiang University), and took on the state’s mission to digitalize and protect the cultural relics of the Grotto Temples.
The institute’s digitization team has long been committed to combining scientific research with archaeological practice, and has always strived for the authenticity and solid scientific basis of its results by using the latest available technologies. Of late, the team has also made outstanding achievements in highfidelity digital archiving of cultural relics, employing the FARO ScanArm and FARO Focus to meet the requirements of various scanning projects.
The digitization team from the Cultural Heritage Research Institute of Zhejiang University first used the FARO ScanArm when it was called upon to digitize cultural relics from the collection at the Xi’an Forest of Stone Steles Museum. The 3D digitization project required the team to obtain data of the steles, so that a replica of the original relics could be produced. This was a very tall order, because the surface of a stone stele often contains small and tightly spaced inscriptions – which can total hundreds upon hundreds of characters that are a mere 2 – 3 cm each, with additional features such as complex strokes and calligraphy style to capture. This meant that the outline and depth of carving must be recorded to extreme precision, so the device used for scanning the stone steles must be able to deliver high-accuracy data.
In the early stages of working on the project, the team considered using a structured light scanner. However, as steles and epitaphs are typically cuboids with six surfaces, the team would have had to take multiple scans at multiple angles if they used that method. Also, it would have been hard to tell during the scan process whether any important information was omitted. More importantly, the method could not guarantee the accuracy of the spliced data.
The project team then decided to test the FARO ScanArm on a lease, and they were very satisfied with the overall results. Equipped with blue light scanning technology, the FARO ScanArm obtained 2,000 actual points on each scan, providing very high scanning accuracy, even across surfaces of different materials. While obtaining scans, the operator could instantly tell with real-time feedback whether any area of the relic had been left out. Using the ScanArm, a stone tablet only required two scans – front and back – to complete the digitized record.
With this positive experience, Cultural Heritage Research Institute of Zhejiang University officially purchased a FARO ScanArm in 2014. Since then, the team has used the equipment many times in digitization projects involving Buddhist stone statues in Shandong’s Qingzhou Museum and with other cultural relics from various museum collections.
A team member uses the FARO ScanArm to perform scans on stone steles in the Xi’an Forest of Stone Steles Project.
Professor Diao Changyu, Assistant to the Director, Cultural Heritage Research Institute of Zhejiang University, added, “For exquisite stone artifacts – such as inscriptions, epitaphs, and especially intricate Buddhist stone statues – we found it necessary to use a scanning device. The FARO ScanArm is able to provide a comprehensive scan in just one scanning cycle, even capturing details in areas that are blocked or inaccessible. Overall, we get very good data consistency and it allows us to achieve a higher level of accuracy, which is impressive. Some stone statues have faint intaglio lines, which are very thin, shallow, and almost invisible to the naked eye. Yet, these show up clearly in the monochrome 3D model obtained by the scans. This is a very important technical means for archeology.”
Apart from the FARO ScanArm, the Cultural Heritage Research Institute of Zhejiang University also invested in a FARO Focus in 2015, to acquire 3D scans of large-scale facades.
Located in Guazhou Country in Gansu, the Eastern Thousand Buddha Caves is one of China’s numerous grotto sites in the Dunhuang vicinity. In this project, the Cultural Heritage Research Institute of Zhejiang University had two main tasks – to map and record the landscape where the grotto is located; and to gather images of the murals.
Aerial orthophotograph of the Eastern Thousand Buddha Caves .
For the landform survey, the team adopted a method that combined aerial photography from an unmanned aerial vehicle, with data collected by the FARO Focus. Through the integration of 3D laser scan data, aerial images, and image-based 3D reconstruction, the team generated a color 3D model of the ground. The orthophotograph is based on the 3D model, and each point in the figure is based on data of precise elevation information and ground GPS coordinates.
For the high-fidelity digitization of the murals, the team employed a technology that combines photo-based 3D modeling with data obtained by the FARO Focus. With nearly two decades of experience in digitizing murals, Zhejiang University had developed a complete set of technologies for photo-based 3D modeling. The team knew that the walls of grottoes and murals had to be treated as 3D objects, because they typically possess a certain level of curvature, varying degrees of relief, and even cracks. For these reasons, the project team hoped to achieve a combined effect between the photo-based 3D model and laser scan-based 3D model.
Obtaining measurements of the Seventh Cave in the Eastern Thousand Buddha Caves with 3D laser scanning.
Prior to using the FARO Focus, the team relied on a total station to collect the dimensional information of the caves. With that data, they made calculations to achieve a more accurate model, after going through thousands of photographs. A major shortcoming of this method is that the shape of a grotto can be well constructed from the total station’s measurements of a few dozen points, but the number of points required for photographic calculation is as high as tens of millions or hundreds of millions. It would have been impossible to verify this against the few points from the total station. Because of the need for better authenticity, the team was therefore prompted to look for a better solution.
The FARO Focus is a market-leading laser scanner with impressive scanning capabilities for capturing large-scale façades, digitizing the surrounding environment quickly at 976,000 points per second. For this project, the device accurately captured the curvature information of the wall surfaces in the grotto caves, and the point cloud data retained the gray values of the measured points. This gave the team very good support for data validation in the later stages of the project.
In the digitization of the mural, the team first used the data obtained by FARO Focus to construct accurate 3D models of the caves. After that, they used their self-developed software to enable the automatic mapping of photographs onto the 3D models, to obtain high definition digital documents of the murals in color. The resulting quality of the mural’s digital images were much higher than 300 dpi.
3D model of the Seventh Cave, after multi-image 3D reconstruction and FARO scan data calibration.
The Cultural Heritage Research Institute of Zhejiang University also used the FARO Focus widely in other archaeological projects. Another noteworthy project is the 3D digitization of the Song Dynasty Ancient Ship of Quanzhou Bay.
The Song Dynasty Ancient Ship of Quanzhou Bay was excavated in 1974 and is presently preserved in the Quanzhou Maritime Museum. Measuring 24.20 m in length and 9.15 m in width, the medium-sized seagoing wooden sailboat was built in Quanzhou during the Song Dynasty. After restoration, the ship now measures 34 m long and 11 m wide, and has an estimated displacement of nearly 400 tons and a carrying capacity of 200 tons.
It is an ancient shipwreck and one of China’s most welldocumented archaeological discoveries, due to its large volume, time of origin, and its relatively well preserved condition. It has been speculated that this may have been the only seagoing ship from China that successfully plied the ‘Maritime Silk Road’ and returned to China.
The ship’s hull had suffered serious damages due to various factors and there was a pressing need to capture its current state to facilitate the laying of the scientific foundation for its protection. Before the Cultural Heritage Research Institute of Zhejiang University was approached for help, two other companies had tried their hand at digitizing the ship, but they were unable to deliver the desired results.
In this project, the team first used the FARO Focus on the hull for large-scale, localized high-precision 3D point cloud data collection. After scanning from a dozen angles, the team successively obtained a relatively complete 3D point cloud data of the hull. With that data, they built a precise 3D model of the hull. At the same time, the team also took hundreds of photographs of the hull from various angles. When fed into the institute’s self-developed software, the photographs were automatically mapped onto the 3D model of the hull, generating the final 3D digital documents of the ancient ship with rich detail and accurate shape. Professor Diao concluded, “We have been using laser scanners in archaeology since 2001, and have come across many different brands of scanners.
Scanning the hull with the FARO Focus.
The overhead orthophotograph map of the ancient ship.
The overall performance of FARO Focus is better suited to our application. Its biggest advantage is its high portability.
When there is an urgent project, one person can take this equipment out to the field for data collection, which is unmatched by other equipment. At the same time, the device provides very good stability. Many of our projects are very time-sensitive, and many of them require scanning in harsh environments. For example, we once did an outdoor scan with the FARO Focus, under low temperatures of -10°C, where even SLR cameras could not operate normally. We have also managed to perform scans successfully at high altitudes. The device functions well even at elevation levels of 4,300 to 4,400 m.”
Commenting on the future prospects of 3D digital technology in heritage preservation, Professor Diao stated, “The aging of cultural relics is irreversible, so it is imperative to record whatever information we have remaining today. The digitization of historical artifacts is a huge responsibility. Our goal for the future is to make holographic record a reality, along with the continual improvement of digital dimension and accuracy. I believe that technological advancement will provide us with the perfect solution to tackle these problems. The other issue is to improve on cost and speed – we need automated and cheaper options to speed up the digitization of cultural relics. The information needs to be recorded quickly, before they disappear forever. By then, it would be too late.”
The Cultural Heritage Research Institute of Zhejiang University was established on March 12, 2010. It comprises the Science and Technology Archaeological Center, Cultural Relic Protection Materials Research Center, Ancient Building Protection Research Center, Art and Archaeological Research Center, and Unearthed Literature Research Center.
The Institute has made outstanding achievements in areas such as digital archeology, geophysical archeology, and research and application of cultural relic protection materials. In 2016, it received approval to set up the State Cultural Relics Bureau’s Key Scientific Research Base (Zhejiang University) for the Digitalization and Protection of the Cultural Relics of the Grotto Temples, and it assumed the state mission in digitalization direction for the Cultural Relics of the Grotto Temples.
For more information, please visit: http://chi.zju.edu.cn/
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