## 1 Introduction  
Augmented reality (AR) technology, which shows virtual objects overlapping in the real world, is gaining increasing attention and various AR applications are being developed. These applications were initially developed as mobile AR based on mobile devices, such as smartphones and tablet PCs. The mobile AR systems used the camera of the smartphone to show the real world while augmenting the virtual objects in the camera screen. Since then, smartphones have become widely available, making it easy for anyone to enjoy AR applications. For example, Pokemon Go is the most successful AR mobile game based on the location-based service (LBS). In this game, creatures are registered nearby and the user hunts the creatures that can be augmented through touch gestures [1]. IKEA's catalog application is a typical example of a mobile-based AR application. Early versions of this application used a real catalog of IKEA as a kind of marker. If a user places the catalog in a location where they want to pre-position the furniture, the mobile device recognizes the marker and augments the furniture. With the development of computer vision technology, the floor and wall can be distinguished by a mobile device with Apple ARKit or Google AR Toolkit [2] and the furniture can be placed in the desired position without markers. However, when using mobile-based AR applications, the user is required to continue to hold the device to superimpose the virtual object, which is the most significant limitation of AR based on mobile devices. Since then, AR Google Glass, a wearable device, has been launched by Google and applications based on a head-mounted display (HMD) have been proposed in earnest. Unlike mobile AR, which needs to confirm virtual objects with a narrow display screen, HMD-based AR applications provide a convenient and immersive experience. HMD-based AR can be applied to a wide variety of fields because when the HMD is worn, the object augmentation and manipulation can be performed at the same time by the user. In particular, various AR applications using HMD are expected to be used in teleconferencing, tele-education, military, maintenance, repair operation (MRO) and exhibition [3]. As such, Google Glass has pioneered the market for wearable AR devices by implementing a simple level of augmented reality functionality. Microsoft, on the other hand, has further improved the realization of augmented reality with HoloLens, which provides immersive 3D screens with high-quality realism. Since the HoloLens is actually equipped with the simultaneous localization and mapping (SLAM) function, it can acquire the geometry information of the space in which the user is located and grasp its position. This makes it possible to place virtual objects on the desk or mid-air in 3D space. Then, the virtual object is correctly registered at a specific point and it is possible for the user to watch the object, such as a hologram, by moving around it. Interfaces developed for 2D display [4], such as a keyboard, mouse, touch screen and a stylus pen in existing computer and mobile device environments, are difficult to use smoothly in an AR environment where objects are registered and manipulated in real 3D space, such use HMD-based AR [5]. This is because these user interfaces have a 2D input method that cannot control the z-Axis (depth) [6]. So, with the increasing number of applications and usage scenarios involving augment 3D virtual objects in the real world and interactions with them, there is a growing demand for bespoke AR interfaces that work naturally within a 3D AR environment. Even the most advanced HMD AR device, the HoloLens, lacks an interface that allows for easy interaction. Although the precise selection and manipulation of objects are among the most important issues in the 3D AR environment [6], the current gaze-assisted selection (GaS) interface of the HoloLens is somewhat inaccurate and has poor usability [7].