## 2 Related Work
### Sensor-Based Approach  
The second research approach is the use of a sensor-based controller and ray-casting technology, which has been studied for a long time in the VR field [5]. HTC Vive, one of the most popular VR devices, has already implemented ray-casting using a controller [16]. However, this requires two external trackers and requires a separate dedicated controller so that it can be used only in a limited environment. In the GyroWand [17] study, it was possible not only to use the ray in the form of a line but also to adjust it to a volumetric form if necessary. This was done to increase accuracy when selecting objects at a distance. In this study, however, there were limitations in addressing only object selection among various object manipulations. Most similar ray-casting studies [5; 14; 15] have focused on object selection and few studies have addressed other object manipulations. As we can see from the interfaces used for VR applications, it is often necessary to select the type of manipulation via the object selection and the pie menu or the traditional linear menu. HoloLens also shares the same issue. As mentioned earlier, this raises the problem that the object manipulations must go through several steps and this method is not intuitive. In the study of [PERSON] and [PERSON] [7] on the HoloLens interface, the object was resized and rotated using a two-hand interface but the problem of fatigue, which was associated with the default interface of HoloLens, remained.  
The computer vision-based interface is intuitive and feels natural because it uses the hand. Also, since it is a hand metaphor, little learning is required and the tasks of selecting (grabbing) and manipulating (translation, rotation, scaling) are performed continuously. However, the range that can be used is limited to the distance the user can extend their arm and in order to manipulate the remote object, the user always has to move near the object. On the other hand, controller-based interfaces mainly use ray-casting technology. Ray-casting technology allows the user to select an object through additional tasks (button selection, gesture or voice) after pointing at an object at a distance (laser pointer metaphor) and intersecting the ray. Therefore, it is less intuitive and natural than the hand manipulation method. To solve this problem, [PERSON] et al. [13], developed an approach in which one hand is used as a pointer metaphor to point to and select an object and then, when manipulating the selected object, the object is replicated in front of the user, allowing the other hand to use the same manipulations as existing vision-based interfaces. However, since the research used only one hand for object manipulation, they could not propose an object scaling method, which is one of the basic object manipulations. Also, their study was limited in that quantitative and qualitative analyses were not conducted to test whether this method is effective for users. In other words, traditional ray casting interactions still have used obtrusive and unintuitive methods such as pop-up menus for rotation, selection and translation. So in this paper, we proposed an object manipulation method that can be easily used by ordinary users. In other words, if the previous work [5] focuses on the selection of objects, this paper address manipulation such as rotation, selection, translation after performing selection.