3D digitization of cultural relics began in late 20th century. It is an important technology that gained popularity in the field of cultural relic conservation after the world entered the digital age. For cultural relics, 3D digitization is to collect the form and spatial and color features of the cultural relic surface through digital means and process the information to reproduce the textures and models. Through 3D digitization, a cultural relic’s appearance, form and color can be converted to digital data, which not only allows for digital archiving, but also provides more means for the conservation, research and display of cultural relics with greater convenience.

Examples of 3D cultural relics

After three decades of development, the technologies, methods and equipment for 3D digitization of cultural relics have become mature and are widely used both in China and overseas. The major techniques involved are 3D scanning and multi-image 3D reconstruction through photogrammetry.

3D scanning is a new technique that integrates optical, mechanical, electrical and computer technologies. It is mainly used to obtain the spatial coordinates of an object’s surface by scanning the object’s spatial features, shape, structure and colors. Based on the volume of the scanned object, 3D scanning is divided into scene scanning and small object scanning. Scene scanning refers to the technique of using a 3D laser scene scanner to obtain high-precision, high-resolution 3D point cloud data of an object's surface. And small object scanning refers to the technique of using a handheld laser scanner or structured light scanner to scan relatively small objects that require high precision.

Scene scanner                Handheld scanner

Photogrammetry is a technique of collecting the shape, size, position, characteristics and inter-relationship data about the target object by processing photographic images generated by the optical camera. Depending on the volume, height, size and precision requirements of the target object, the data collection can be carried out with drones or digital cameras.

Low-altitude photogrammetry from a drone

Close-range photogrammetry

In the Joint laboratory and the joint research project, research is carried out on the application of ultra-HD 3D digitization for cultural relics to make achievements on innovative application of the technology.

For large and immovable cultural relics, 3D digitization is usually realized through a combination of 3D scene scanning and close-range photogrammetry. Spatial features can be obtained through 3D scanning, and texture information can be obtained through close-range photogrammetry. With the combination, a textured 3D model for a cultural relic can be generated.

The project has carried out research on coded targets for 3D laser scanning, using coded targets to improve the precision of control. Meanwhile, common target markers are shared between 3D scanning and photogrammetry to reduce the control workload and realize integrated control of the two techniques for high-precision digitization of cultural relics.

Object detection with AprilTag targets

For small and movable objects, data collection and 3D reconstruction are realized through close-range photogrammetry or a combination of this technique and 3D scanning.

The project has carried out research on the methods and devices for integrated control of 3D scanning and photogrammetry, which can not only result in high control precision but also significantly improve efficiency.

Device for integrated control of 3D scanning and photogrammetry

When the device is used independently in 3D reconstruction through photogrammetry, its QR code can help realize automatic ground control points (GCPs) without manual tie points (MTPs). Compared with MTPs, GCPs can significantly improve control precision, reduce the heavy manual work required by MTPs, and help avoid the issue of varied control precision caused by differences in the tie points marked by different operators. When the device is used independently in 3D scanning, its target ball can be used to realize scanning control and assembly during the process, and markers can be sticked to the frame of the device when needed so that the essential markers don't have to be sticked to the cultural relics for scanning. This is a helpful feature, as it is not allowed to stick markers to cultural relics by rule. When the device is used in both 3D scanning and 3D reconstruction through photogrammetry, it can help realize highly aligned precision between the scanned model and the photogrammetry model, which is far superior to manual alignment. Moreover, the alignment is completed automatically in the process of data collection and processing, which reduces much workload and helps produce digitized cultural relics that highly match the originals.

The project plans to provide a full demonstration on the integrated application of the 3D digitization technologies for cultural relics with the remains of the Bower of the Spirit Pool (Lingzhao xuan), a stone cultural relic from the Palace Museum, and bronze vessels from the Three Star Mound (Sanxingdui) as the research subjects. The project will study the methods, supporting hardware, and processing techniques for data collection of the fundamental spatial features and texture information, as well as the special characteristics and differences in ultra-HD 3D data collection and processing, so as to formulate rules and standards for collecting and processing 3D data and provide technical solutions with highly consistent results, little manual intervention, quantifiable process and result evaluation and easy implementation. Additionally, the project seeks to form a cultural relic digitization achievement system and create rules and procedures for data collection and processing based on the value of cultural relic data to better conserve, display and utilize cultural relics in a prospective way. Ultimately, the project hopes to accelerate the promotion and application of China’s advanced digitization technologies in the field of cultural relic conservation, encourage the transfer of related scientific research results to the production sector, better utilize the rich cultural relic collections from the ancient Greek civilization and the classical Chinese civilization, and play a leading role among the countries along the “Belt and Road” in strengthening mutual appreciation on cultures and civilizations.