# Real-Time Motion Adaptation with Spatial Perception for an Augmented Reality Character
## 1 Introduction  
Augmented reality (AR) will be increasingly used as a technology that integrates digital information and virtual objects with real environments [1, 2]. AR systems have been recently applied in various fields, providing the use of digital contents to combine the real and virtual worlds [3, 4]. For example, Pokemon Go merged real activity and interaction with digital objects (e.g., virtual characters) in the user's surroundings [5]. More recently, many researchers in AR fields have begun to actively study the increase in users' perception to resolve the environmental differences between real and virtual spaces, such as light conditions [6] and geometric relationships [7]. AR systems based on a virtual character that moves and interacts have allowed for a higher sense of being there with the virtual character; however, it is difficult to match the character's motion in real space [8]. In ongoing recent research, there have been many attempts to resolve the differences in spatial configuration in the real world with respect to motion adaptation [9]. There has been a lack of study on how to adapt using spatial perception in terms of practical deployment. In particular, it is important to match the virtual character's motion based on spatial configurations in order to visualize the environmental conditions of the real world [10]. To overcome this problem, we present a novel method of real-time motion adaptation for an AR character using spatial perception based on relationships between a virtual character and the configuration of its surrounding environments, and we introducea procedural approach for implementation, which had not been previously studied. Thus, we investigate a method for preserving automatic motion adaptation to adapt motion to environmental differences using original motion datasets. Also, this paper proposes a context-aware AR adaptation method for improving the AR experience of participants.  
Figure 1 shows an example of adapting character motion in the AR system. The character can naturally match with and adapt to the spatial configuration in the participant's environment. For example, the participant in the AR environment can interact with the virtual character. In this case, the character should exhibit natural movements to adapt to the real configuration (e.g., ice vs. puddle). Our method in this paper focuses on adaptive motion in the AR space rather than spatially correct motion. We identified real objects in the environment, and then the AR character was designed to move according to the real environmental situations regarding the context of the AR participant. To adapt the motion of the AR character to the real configuration, we predicted the real objects using a detection process. Then, we decided on adaptive motion by considering the location of the detected object and its characteristics. Also, we then estimated the 3D position for the AR character.  
The structure of the remaining part of this paper is as follows: Section 2 gives an introduction and future directions with related works. Section 3 presents the overall system configuration, and Section 4 provides a detailed explanation of the implementation of the proposed approach in this paper. Section 5 presents the evaluation results of our approach in terms of adapting to environmental conditions and reports the main results, including those related to co-presence. Finally, in Section 6, we conclude this paper and suggest future research directions.