## 1 Introduction  
Augmented reality (AR) overlays computer-generated visual information--such as images, videos, text information, and 3D virtual objects--onto the real-world [1]. Unlike virtual reality (VR), which immerses the users inside a computer-generated environment, AR allows the users to see the real world with virtual objects blended within the real environment and enables the users to interact the virtual content in real-time [2]. The increasing computational capabilities, powerful graphics processors, built-in cameras, variety of sensors, and power of cloud-supported information access have made AR possible using handheld mobile devices, such as smartphones and tablets [3]. The evolution of AR technology--from the heavy wearable head-mounted display (HMD) devices to smartphones and tablets--has enabled new and rich handheld mobile AR experiences for everyday users. In handheld augmented reality (HAR), users can see the real world overlaid with virtual information in real-time by using the camera on their mobile devices. Current mobile devices are small in size, lightweight,and portable enough to be carried wherever users go. With this ubiquitous availability, HAR allows us to develop and design innovative applications in navigation, education, gaming, tourism, interactive shopping, production, marketing, and others [3]. Thus, smartphones have been identified as an ideal platform for HAR experiences in various outdoor and indoor environments [4; 5; 6]. In order to interact with the virtual world using HAR displays, a user needs to position and orientate the device using one hand and manipulate the virtual 3D objects with the other hand. In general, the touchscreen is used as a primary interface to interact with AR content [7; 8]. In addition, the various built-in sensors in the handheld devices--such as cameras, GPS, compass, accelerometers, and gyroscope--enable to precisely determine the position and orientation of the device in the real world (e.g., [8; 9; 10]). Furthermore, the device's camera is used to naturally capture the user's mid-air hand movements while holding the device [11; 12]. Like in HMD AR, manipulations such as selecting and moving virtual 3D information are primary interactions in HAR devices [13]. The existing HAR interaction methods, such as touch input, offer promising solutions to manipulate virtual content (e.g., [14]). However, they still have substantial limitations. For instance, touch input is limited by the device's physical boundary and usability suffers as on-screen content becomes occluded by finger (i.e., finger occlusions [15; 16]). Also, 2D inputs on the touch surface do not directly support manipulating the six degrees of freedom of a virtual object in the augmented world [17]. Unlike touch-based input, device movement-based HAR interaction methods support 3D object manipulations (e.g., [8; 9]). However, orienting the device to rotate the 3D virtual objects might force the users to lose sight of the manipulated virtual object in the display. A mid-air hand gesture input method supports more natural and intuitive interaction for HAR applications (e.g., [11; 12]). Nevertheless, using the back-camera on the device to track the hand and finger movements is often not feasible, due to several factors such as (1) it may not be very accurate, (2) the device should be held at a certain distance from the user's eye, and (3) the human arm has a very limited region of reach. Furthermore, interactions with handheld devices also have issues, like social acceptance, when performed in front of unfamiliar people [18]. With the recent developments in fabric-based technology and new types of electronic textiles and smart clothing [19], we are witnessing [PERSON]'s dream--of computers that \"weave themselves into the fabric of everyday life\" [20] --has taken one step closer to reality. Integrated into users' clothing, fabric sensors are able to unobtrusively detect user movements [21] to convert them into input methods to control modern devices (e.g., [22; 23; 24]).