"We conducted three-dimensional modeling of the whole cave 13 of Yungang Grottoes, took 283400 high-definition images, and the original images exceeded 13tb. The software independently developed by the team synthesized the ultra-high-precision three-dimensional digital model of cave 13 and designed several platform application scenarios." at the 2021 China Geographic Information Industry Conference held in Wuhan in October this year, The presentation on the achievements of digital protection of cultural heritage made by Huang Xianfeng on behalf of the team attracted the attention of many participants. "Digital Yungang" is one of the projects continuously researched and developed by Huang Xianfeng team in recent years. Nowadays, more and more returned students have joined the ranks of cultural heritage protection. With the help of modern photogrammetry and remote sensing technology, the three-dimensional digital reconstruction of cultural heritage is giving cultural relics eternal charm beyond time and space. "Clone" Grottoes As the camera slowly moves forward, Maitreya, the main Buddha in cave 13 in Yungang, after the baptism of time, still looks outstanding in the mottled, wearing a crown, smiling eyebrows and eyes, and vaguely visible chest accessories, showing his dignity and solemnity. Under the elbow of the right arm of the main Buddha, which is about 13 meters high, one Hercules and four arms lift it vigorously, which is as powerful as pulling up the mountain. Suddenly, cave 13 seemed to be in front of us. Such a picture is "cloned" from more than 280000 high-definition images, and the whole grotto model is almost unchanged. At the same time, the three-dimensional display system combines several functions such as roaming display, knowledge map information and grotto disease annotation. It can also provide various forms of three-dimensional models, real high-precision location information, measurement tools and archaeological map output services, so as to provide assistance for the research and protection of Yungang cultural relics. Dashi Intelligent Technology Co., Ltd., which sprouted in the State Key Laboratory of surveying, mapping and remote sensing information engineering of Wuhan University, is the technology provider, and Huang Xianfeng is the founder of the company. He told reporters that the technology provided by the team for "digital Yungang" has achieved two major breakthroughs: "first, the application is convenient, and mobile phones, tablets and computers can be used as carriers; second, a data defense mechanism has been established to ensure the security of private and shared data." "Hundreds of thousands of photos will have seams between two pairs, and large clusters are needed to deal with seams and color difference." since the first visit to Yungang Grottoes to investigate the feasibility of the project in 2015, it took Huang Xianfeng three years to update the three-dimensional reconstruction technology to meet the digital modeling needs of such a large volume of Yungang Grottoes. "We can't do porcelain work without diamond. After a lot of technical exchanges and pre research with the director of Ningbo Digital Center of Yungang Research Institute, we didn't dare to really start the project until 2018. Then it was three years, and the acceptance of cave 13 was finally completed in the first half of this year." Huang Xianfeng said with emotion. To complete the digital real reproduction of cultural heritage, we need to focus on the development of key software and hardware technologies such as high-precision collection, digital reconstruction and three-dimensional application of the real world, which is the advantage of Huang Xianfeng team. "Making the application of photogrammetry technology easier has always been our goal in the process of entrepreneurship and R & D. the purpose is to make it easy for everyone to carry out 3D modeling like taking photos, record everything in the world and understand the world with real 3D data." Huang Xianfeng said. Origin Dunhuang In 2007, Huang Xianfeng, who had just graduated and stayed in school for a short time, received a special and unforgettable task - together with more than a dozen Wuhan University researchers, led by Zhu Yixuan, Professor of the State Key Laboratory of surveying, mapping and remote sensing information engineering of Wuhan University, they went to Dunhuang. They wanted to conduct three-dimensional scanning of Mogao Grottoes through excitation equipment, take cave photos, and finally process data. That was the first time Huang Xianfeng participated in cultural heritage protection. He can't remember how many times he went back and forth between Wuhan and Dunhuang during that time. Relying on the tools that now seem extremely poor, he completed the facade photogrammetry of cave 158 again and again. However, the initial measurement accuracy is low, the speed is slow, and the effect is not good. After denoising, stitching and other technical processing, it is still unable to accurately restore the color and texture of the cave. "Generally speaking, two-dimensional photos are planar, but the Buddha statues and murals in the grottoes are not. The most difficult thing is to 'align' the plane and surface, and use cultural relic mapping technology to achieve accurate digital reproduction." they realized that the traditional surveying and mapping technology can no longer meet the modeling and calibration work with doubled complexity. In order to successfully complete digital replication, new modeling software must be developed. The wind and sand roared in Dunhuang. In order to take care of it, Huang Xianfeng, doctoral students Zhang Fan and Zhang Zhichao simply shaved their hair and buried themselves in the research of software tools. Zhang Fan wrote the code and Huang Xianfeng did the debugging. The three people worked in rotation. After nearly three months of attempts, a software called "mapping master" was officially born. It can realize the high-quality texture reconstruction of grotto cultural relics, thus clearing the technical obstacles for data acquisition. After the team's step-by-step scanning, measurement and model construction, two years later, the idea of reproducing Dunhuang has finally become a reality, and the full picture 3D data can be well displayed. Modeling spatio-temporal In 2011, Huang Xianfeng went to Zurich Federal University of technology to continue to engage in relevant scientific research of photogrammetry. This experience gave Huang Xianfeng a deeper understanding of the digital protection of cultural heritage around the world, and also made him start to think about an important proposition - how to complete the protection of cultural heritage with lower cost technology. "Some countries have sufficient funds, and the cultural heritage protection work is carried out early, and the effect is good; on the contrary, some countries lack funds and manpower, and the current situation of cultural heritage protection is actually very bad. If the cost of relevant technologies is lower, the threshold of digital reconstruction can be reduced," Huang Xianfeng said. He did find a way. Use portable photography equipment including mobile phones to shoot cultural relics in different directions and angles, upload the photos to the get3d background page developed by his team, and wait more than ten minutes to obtain clear 3D modeling results of cultural relics, so as to realize digital preservation. "We call this lightweight 3D modeling technology g-engine2.0, a new generation of artificial intelligence cloud computing 3D modeling engine. When users turn on their mobile phone and touch the Photo button, they can reproduce the 3D world and everyone can model." compared with lidar scanning, this technology has low cost and is easier to operate. After the acceptance of the three-dimensional reconstruction project of Yungang Grottoes, Huang Xianfeng and his team started the digital reconstruction of Maijishan grottoes and kuci grottoes. "We still have a lot of work to do to make more cultural heritages immortal in the digital space. Digital rebirth is not only for research and protection. By broadening the display means, we also hope to narrow the distance between cultural relics and the public, so that more people can understand and love cultural relics," Huang Xianfeng said. (outlook new era)