# Augmented Reality in Cultural Heritage: An Overview of the Last Decade of Applications
## 3 Top Trending Applications of AR in Cultural Heritage
### Three-Dimensional Reconstruction  
Ancient artifacts carry invaluable information about the culture and civilization of a society. However, they are often not well preserved or are inaccessible because of their size and fragility. It is estimated that in the past ten thousand years, more than 90% of humanity's cultural heritage has been lost [26]. The merging of 3D reconstruction and AR for cultural heritage is currently becoming an emergent technology [27]. Three-dimensional reconstruction technologies show great potential for the digital preservation of CH artifacts [28; 29; 30]. Research in this field started before 2010, so a review published in 2009 lists several projects related to AR and virtual heritage [31]. The 3D reconstruction process consists of a sequence of steps [32]. The first and fundamental step is obtaining the initial data collection by using several technologies, among which the relevant ones for CH artifact reconstruction are: photogrammetric 3D modeling, triangulation and time-of-flight laser scanning, structured light, stereo-calibrated optical sensors, and mobile lidar. Photogrammetry is one of the most often used methods in the 3D modeling of CH artifacts [33; 34]. However, it relies on a considerable number of images and an increased computation time for an efficient reconstruction. Therefore, it takes more time to converge. On the other hand, the 3D geometry-based modeling approach depends on a depth-sensing camera which is often too expensive for many applications. Recent works propose methods to obtain information about depth using lasers or structured light [35]. A laser scanner is a high-quality 3D solution that allows creating models by scanning any surface--from stone to wood, metal, and many more--but the hardware equipment is expensive and complex software is needed to process data [36; 37; 38]. The recent development of lidar technology and the integration with a mobile platform enables adequate speed and accuracy for large CH sites [39]. One image is not enough, in most cases, for a complete representation of a 3D model [32]. The artifact images may have several different viewpoints. The next step in the 3D reconstruction is the alignment of color and depth information. The alignment of range images can be performed by using the iterative closest point (ICP) approach [31]. When the registration is accomplished, all the generated 3D views are combined in a single mesh. In the final stage, the 3D model is textured for a realistic representation of the  
Figure 5: The 10 most active countries by number of documents (**a**) and citations (**b**). digital CH artifact. The selection of the optimal solution for the 3D reconstruction is a challenging task. A method that combines several techniques for 3D object restoration for AR applications is presented in [40]. The solution includes obtaining the 3D point cloud of the CH artifact using a 3D scanner device, processing and reconstruction of the 3D model using Meshlab, and building the AR application for the visualization of the restored CH artifact. AR provides a method that enables experiencing a 3D reconstruction of a CH artifact (see Figure 6) with a high level of detail and with a full-scale dimension of the space perception, without requiring the user to have specialized knowledge [41; 42]. Three-dimensional models in combination with AR enable the general public to better understand and experience history through more intuitive and interactive means [43; 44; 45]. Furthermore, the 3D reconstruction of CH artifacts can be used for 3D replications that involve combining digital touch screens, AR applications, and high-quality 3D printing. The subjects that evaluated 3D AR considered the use of reproductions or physical 3D prints intuitive, mainly for contextual understanding and intangible experiences [46]. AR is used for the restoration of deteriorated religious objects [47] and can help to revive these important CH objects [48].