# A Review on Augmented Reality in Education and Geography: State of the Art and Perspectives
## 2 Historic Overview of AR  
One of the first pieces of equipment that enables a human to connect with the immersive environment is the \"head-mounted three-dimensional display\" (HMD), developed by [PERSON] at Harvard University and described in the paper [2] in 1963. The system features a unique headset that uses cathode ray tubes (CRTs) combined with eyeglass-like optics to deliver separate 2D visuals directly to each eye of the user. By using the headset, the user has a 40-degree field of view of the image that is presented. Moreover, to ensure the safety of the user, the CRTs are mounted in a metal that is fully grounded. Then, as the user moves their head, a head position sensor, which can be either mechanical or ultrasonic, measures the head position coordinates. Unfortunately, this system does not let the user move freely in the room, and it can only move their head up, down, right, and left. The mechanical head sensor is constructed from a ceiling-mounted arm, and it is allowed to rotate above a vertical pivot. The position of each joint of the arm is measured, and the coordinates of the position of the user are identified. The coordinates of the headset are further fed to a computer that calculates the elements of a rotational and translational matrix of the perspective of the user. This can be performed through perspective transformation, depicted in Figure 1, by using simple relationships, (1) and (2), to transform from a particular point in space (in this case, the human eye) to a screen. \[X_{s}=\frac{x}{z}\times\cot\Bigl{(}\frac{\alpha}{2}\Bigr{)} \tag{1}\]  
\[Y_{s}=\frac{Y}{z}\times\cot\Bigl{(}\frac{\alpha}{2}\Bigr{)} \tag{2}\]Together with the room coordinates stored in translational and rotational matrices, the image in the eye coordinates is formed and sent to the clipping divider. The clipping divider has the role of eliminating any outside region that can exist in the image formed previously, such that the correct image is shown to the user. In the final stage, the image is processed by the Analog Display Driver, which transmits it to the CRTs using analog signals. The whole process can be observed in Figure 2.  
Going back further, in the 1990s, the VR and AR applications kept on getting developed better and better because of the fast development in the technological domain. For example, in 1992, the CAVE Automatic Virtual Environment was developed and presented by the Electronic Visualization Laboratory in Chicago [3]. The system allows the user to enter a cube formed by four screens, on which images are projected. These images are stereo images, and, because of this, the user must wear 3D glasses, creating in this way the immersive experience. This system was initially thought to create a virtual world for scientific research because it was easier and more user-friendly to test different theories and practical applications. Next, in the modern era of applications in the AR and VR domain are the Google Glasses, which were developed in 2013. The glasses developed by Google are convenient and can even substitute a smartphone because this product is a wearable computing product [4]. A wearable computing device is a device that is easy to wear every day, on clothes or under them, and has high computing capabilities. Moreover, it allows for interactions with the internet through natural language voice commands or through physical touch of the glasses. The physical components of the Google Glass can be seen in Figure 3 and are the following: video display, camera, speakers, button, microphone, glass frame, and the glasses. Figure 1: Perspective transformation, where (x,y,z) are the points in 3D space, (X\({}_{\text{S}}\),Y\({}_{\text{S}}\)) are the points on the screen and \(\alpha\) is the field of view angle. Figure 2: Operational block of HMD.