# A Review on Augmented Reality in Education and Geography: State of the Art and Perspectives
## 6 Augmented Reality Sandbox
The distance from the laser scanner to a single point on the clay can be determined, by using the following equations, Equations (3) and (4), where B is the distance between the laser emitter and the camera that detects the reflecting laser, \(\theta\) is the angle between the laser emitter and the clay's reflected laser, as seen from the camera and \(\phi\) is the angle at which the laser is emitted from the laser emitter. \[X=B*\tan(\theta) \tag{3}\]  
\[Z=\frac{B}{\tan(\phi-\theta)} \tag{4}\]  
The angles and distances are also described in Figure 9, where A is the laser emitter, D is the camera, C is the Minolta Vivid-900, E is the clay, and F is the worktable. One of the drawbacks described by the author of the paper when using this type of laser scanner is that it was designed to take only single scans of the objects, without the possibility of detecting if the object's form has changed. To overcome this issue, the authors had to use the software development kit of the laser scanner: Minolta Software Development Kit (SDK). Through this, they could force the laser scanner to scan the clay every 1.2 s, simulating a real-time environment. The worktable can be anything, ranging from a simple table made of wood to glass, because the area of interest in this case is the model, the clay, which acts as input/output. After the clay is scanned, the model is converted to DEM, which is the Digital Elevation Model. The DEM is the standard used in the geographical science and in topography to store the information [35]. Using the Digital Elevation Model, the authors managed to implement a couple of functions that the users can play with. For example, the users of Illuminating Clay can read the slope variation and curvature in different points, which were computed by applying two Sobel Filters to determine the x and y derivatives of a certain point on the topographic map. Then, the slope value is shown on the clay by using a color map, where red represents the highest value and purple is the lowest value. Another function is the \"Shadows and solar radiation\", which allows the users to observe how the shadows would be projected for different positions of the Sun. Also, it is possible to simulate a whole year timelapse to determine the radiation coming from the Sun at a certain point. This could be useful when the user wants to simulate different conditions for crop management, housing complex buildings, or solar energy collectors. Lastly, the user can use the \"Water flow and land erosion\" function to simulate the consequences of  
Figure 9: Representation of the trigonometry done by Minolta Vivid-900. intervening in the natural environment and how the water would affect the surroundings in that case. This can be useful in case somebody wants to build houses, dams, roads, or other constructions that affect the natural environment. For this, the authors developed an algorithm that computes in real time the local drain direction, but they also used some of the functionalities from the GRASS open-source library. Following the implementation of Illuminating Clay, the same authors, [PERSON] et al., describe another way of implementing the AR Sandbox device. In the same paper, the authors describe the SandScape, which is depicted in Figure 10.  
The device is based on a box (D) containing 1 mm diameter glass beads (C), which are lit from beneath with 600 high-power infra-red light (IR) LEDs (E). Also, to compensate for the uneven distribution of the IR light on the boundaries of the box, four IR mirrors are placed in the proximity of the margins. Then, represented as B in the figure, the IR camera senses the intensity of the light that passes through the volume made by the beads. By performing this, the depth of the model can be obtained, as more lit zones mean a lower level and less lit zones mean a higher altitude.