[Abstract] : This paper summarizes the concept and characteristics of augmented reality and focuses on the application status, application scenarios, existing problems and future development trends of AR technology in restoration of historic sites and protection of digital cultural heritage.

Keywords: AR, historic site restoration, real scene, virtual information, cultural heritage, digitalization

1. The concept and characteristics of AR

1.1 AR Concept

Augmented Reality technology is a clever fusion of virtual information and the real world technology, also known as Augmented Reality, widely used multimedia, THREE-DIMENSIONAL modeling, real-time tracking and registration, intelligent interaction, sensing and other technical means. Virtual information such as text, image, 3D model, music and video generated by computer is simulated and applied to the real world. The two kinds of information complement each other to achieve "enhancement" of the real world [1].

1.2 Features of AR technology

AR mainly integrates tracking registration technology, display technology, virtual object generation technology, interaction technology, merger technology, with three outstanding characteristics:

(1) Information integration between real world and virtual world;

(2) Real-time interaction;

(3) Add positioning virtual objects in three-dimensional scale space [2].

AR technology can be widely used in military, medical, architecture, education, engineering, film and television, entertainment and other fields. This paper mainly discusses its application in restoration of historic sites and protection of digital cultural heritage.

2. Application status and existing problems of AR in restoration of historic sites

2.1 Application status of AR technology in restoration of historic sites

AR technology is to add some virtual information in real life. It is the real environment and virtual objects superimposed on the same screen or space in real time, so that people can have a more comprehensive, intuitive and dynamic understanding of real things. In the process of restoring historic sites, AR technology emphasizes the function of restoring human vision, and carries out 3D modeling of the surrounding real scenes. Through the camera and data helmet of the terminal, people can see the full picture of cultural relics thousands of years ago and introduce detailed data of cultural relics, so that people's sensory awareness can be strengthened in the real world. The restoration system consists of a computer server, a wireless network, and a PERSONAL data assistant (PDA) client. Through a head-mounted display and special glasses, the restoration effect of damaged or nonexistent monuments can be seen on site from a virtual perspective.

The 360-degree panoramic view of the Forbidden City, the reenactment of the Parthenon abroad, the dynamic demeanor of the Qingming River Picture... Both use augmented reality. During The Beijing International Design Week, the design entitled "Reconstructing Fucheng Gate" is particularly eye-catching. It recreates the buildings that disappeared in the last century through augmented reality technology, and combines the real and virtual with computer vision technology. Nowadays, the rapid development of modernization has accelerated the extinction of ancient monuments. With the slow passing of these ancient buildings, the recognition of memories, historical features and reactions to social conditions that we can retrieve from real life are also gradually decreasing. Through AR technology, some computer-generated images and videos are added when the actual scene is displayed by computer, so that users can interact with virtual things and information to a certain extent. At this time, the virtual cultural relics and historic sites will be integrated with the real relics and specific scenes, through the support of hardware equipment such as display screen, camera, tracking and sensing system, so that visitors can see the text explanation and virtual reconstruction of historical sites.

Recent restoration technologies have achieved remarkable results in famous cultural relics. In the reconstruction of The Old Summer Palace, we abandoned the real site restoration method with high cost, and chose AR technology to restore the former magnificent and glorious scene in real time and intuitively at the site, and formed a sharp contrast with the current site. This project takes the Water method area of Xiyanglou Scenic area of Yuanmingyuan as the background to reconstruct the water method, the line method mountain and its gate, the water observation method, the Sea yan Tang and the east and West water tower [3]. In the real background to enhance the reconstruction of the scene, using three different modes, fixed point single user rotating mirror cylinder, PDA self-help guide, helmet mobile, so that the royal park for a long time to make people regret to reproduce in a real and detailed way, fully reflects the AR 3D modeling technology.

2.2 The problems of AR technology in the restoration of historic sites

However, today's restoration of historic sites is limited to important and famous historical sites, and it is difficult to extend to the historical sites at county and township levels. Local people all have a complex of recalling historical sites and strong emotional color, such as the local county government, Confucian temple, old streets, old hutongs and temples... If AR technology can also be used to complete and reproduce, it will be a eagerly awaited spiritual comfort for local people. In the watch in the process of the instrument, wear, use is also a problem, the current technology to lower popularization application groups, local related infrastructure is not perfect, the economic and financial security is not enough, maintenance and protection technique is not sound, tour visit the culture industry, underdeveloped tertiary industry and so on, have hindered the AR technology and historical restoration in the local application and promotion.

3. Application scenario and technical analysis of AR in digital cultural heritage protection

3.1 Application scenarios of AR technology in digital cultural heritage protection

Cultural heritage is a non-renewable historical and cultural resource. The restoration of cultural heritage and the digitalization of AR technology to show and protect it have unique effects and great significance for the inheritance and development of civilization. The following is the specific research status and the connection between its technology application:

(1) Specific research status

At present, in terms of the application research of digital technology in the protection and development of cultural heritage, scholars Zhou Mingquan and others have analyzed and introduced the commonly used digital technology, equipment and working principle, and elaborated the basic methods of cultural heritage restoration. Scholars liu Jie and others explored the feasibility of 3D printing technology in the restoration of cultural relics and proposed the basic restoration process steps. Taking guizhou minority culture as an example, scholar Wang Hainan studied the application of reverse engineering technology in cultural heritage protection. Taking cloth handicrafts as an example, scholars Lei Man et al. put forward that the application of digital technology can effectively shorten the development cycle and improve product quality, providing a new way for the digital protection and development of ethnic handicrafts [4].

Yin Ruins is the shang Dynasty cultural site in Anyang, Henan Province, and its digital cultural heritage protection has obvious advantages. Digital recording and digital preservation are beneficial to ensure the integrity of Yin Ruins cultural heritage, establish permanent archives and databases, and realize digital reproduction and restoration by using reverse engineering, 3D modeling, virtual reality and other technologies.

(2) Technical application connection

Firstly, 3d scanning technology is used to digitize artworks, cultural relics and buildings to generate digital model libraries and establish digital museums. Secondly, for cultural relics with serious deformation and large damaged area, digital restoration can reduce secondary damage to cultural relics, and the production of the defective part can be completed without contact with cultural relics. Thirdly, digital technology also provides innovative methods for assembling fragments of cultural relics. Fragments are numbered, scanned, modeled and printed to reduce trial and error and damage to the original [5]. The application of digital technology in yinxu cultural heritage can run through the whole process of cultural relics excavation, restoration, publicity and protection. In the early stage of cultural relics excavation, archaeological experts can obtain information such as the storage situation of cultural relics, specific location and current surroundings through detectors and scanners, which is conducive to digital photography of architectural forms.

Three-dimensional data of cultural relics can be obtained through AR's digital capture technology, and certain data of damaged cultural relics can be reverse-derived. AR technicians and cultural relic protection experts can conduct THREE-DIMENSIONAL modeling through these data. Then, 3D printing technology is used for rapid prototyping to achieve complete reproduction without contact, so as to show the audience the whole holographic scene and realize the restoration of digital cultural heritage.

3.2 Technical analysis of AR technology in digital cultural heritage protection

Here, it mainly reflects the three major technical points of AR: THREE-DIMENSIONAL registration (tracking registration technology), virtual reality integration display, human-computer interaction. The process is to first by cameras and sensors for data sampling the real scene, and into the processor carries on the analysis and reconstruction, and then through the AR head show or smart camera on a mobile device, gyroscope, sensors and other accessories real-time update user space position change data in the real environment, so it is concluded that the relative position of the virtual scene and real scene, Coordinate system alignment is realized and the fusion calculation of virtual scene and real scene is carried out. Finally, the synthetic image is presented to the user [6]. Users can collect control signals through AR head display or interactive accessories on smart mobile devices, such as microphone, eye tracker, infrared sensor, camera, sensor and other devices, and carry out corresponding human-computer interaction and information update to realize interactive operation of augmented reality. Among them, THREE-DIMENSIONAL registration is the core of AR technology, that is, virtual information is matched with real scene information by taking two-dimensional or three-dimensional objects in the real scene as markers, that is, the position, size and movement path of virtual objects must be perfectly matched with the real environment to achieve the virtual reality [7]. This kind of technology makes cultural heritage "live".

4. Conclusion

This paper mainly introduces the application technology and application examples of augmented reality technology in restoration of historic sites and protection of digital cultural heritage, and explains the principle and application prospect of AR technology digital processing content (such as digital animation, digital image, sound, text, etc.) through the analysis of examples. Although the current research technology still has many barriers, such as low penetration rate, high price, and defective use experience, but with its strong technical advantages and the progress of emerging disciplines, I believe that AR technology will gradually be applied to more fields, with broader and brighter prospects for development!

reference

[1]. Zhang Yunyan. Research on the application of digital technology in the protection and development of Yinxu Cultural Heritage [J]. Beauty and Times (City Edition), 2021, 4 (05): 116-119.

[2]. Part 3. On the application of digital interactive technology in cultural heritage protection [J]. Science and Technology Wind, 2020, 4 (09): 25.

[3]. Wu Qianhua. Communications World, 2019, 26 (1): 289-290. (in Chinese)

[4]. Li Jingyan. Art Science and Technology, 2018, 31(5): 92.

[5]. Wang Jialu. Application of augmented reality technology in digital protection of cultural heritage: A Review of digital Protection technology and Application of Cultural heritage [J]. Dyeing and Finishing Technology,2018, 40 (11): 97.

[6]. Wang Gang, Li Hao, Lei Xin, Cheng Shiyu. Research on the Application of Digital Technology represented by Augmented Reality technology in Cultural Heritage Protection [J]. Journal of Hubei Institute of Fine Arts,2018, 4 (02):89-91.

[7]. Qilu Chen, Xinxin Liu, Yi Fang, Jue Chen. Application of AR technology in digital protection of intangible cultural heritage. Intelligence, 2017, 4 (32):231.