## 2 Related Work
### QR Codes  
Ebsar is an Arabic system which provides indoor navigation for PVI by preparing the building and then guiding them using navigation commands [41]. At first, this system constructed a graph where each node represents a place or a checkpoint and a QR code is generated for each. Each edge is labelled with the number of steps and the direction between nodes connected to it. To start navigating, it seeks the nearest node to the PVI's location. After finding this node, it searches for the shortest path from that node to the destination node. During navigation, it provides Arabic voice feedback to the PVI using Google Glass. This system used Google glasses to facilitate detecting QR codes and communicating with the user, which makes it inexpensive and allows PVI to navigate without having to use their hands. However, this system requires an internet connection to download the building graphs from the server. Moreover, it is better to use markers which can be detected from a long distance rather than a QR code. Adding haptic feedback enables operation in a noisy environment. AssisT-In used QR codes to help cognitively impaired people navigate inside new and complex environments [42]. QR codes are installed inside the building. Then, PVI use one of them as a starting point by scanning it. After determining the desired destination, the system calculates the shortest path to reach it. The system starts navigation by guiding PVI from the start node to subsequent nodes until reaching the destination node. When PVI scan a QR code during navigation, the system provides a feedback to them as a text message in the voice of a virtual pet such as a cartoon dog. If PVI scan a QR code not belonging to AssisT-In, it notifies them to keep searching for the correct QR code. However, it is difficult for PVI to capture good quality photos with their smartphone camera as most of the photos may be blurry. If more than one QR code is detected at the same time, it is better to select the one to use based on the distance and not select it randomly. [PERSON] et al. proposed a navigation approach using a mobile robot in an indoor environment based on QR codes as landmarks [38]. These QR codes are placed in a distribution such as a grid pattern at the ceiling and the system constructs a map for them. Furthermore, an industrial camera is added to the robot to rapidly identify these QR codes. With this configuration, the camera can detect at least one QR code in its field of view and can estimate the position of the robot. The proposed recognition algorithm can localize the robot accurately and is suitable for real-time tasks. However, the robot failed to recognize QR codes in a completely dark environment. It is also hard to identify QR codes in adverse conditions such as a blurring effect due to motion and occlusion. A smartphone system was developed to help PVI navigate in unknown indoor places using QR codes [43]. It starts by determining the type of current position, then fetching the environmental information from colour QR codes using a simple CV algorithm based on their colour and edges. When in motion, the change in location is computed continuously using two inertial sensors and PVI routes are recorded to guide them during the return route. During navigation, the system provides PVI with feedbacks using beeping or Text-to-Speech (TTS). The proposed method combined spatial language and virtual sounds to provide productive feedback which leads to better performance and reduces navigation errors. This system only requires minor modifications to the environment such as installing QR codes. Coloured QR codes facilitate separating and identifying them from the background. However, objects only within 2.5 m were detected, which needed improvement. In adverse conditions, such as the blurring effect of motion, the system has difficulties identifying QR codes. An android navigation application was introduced for PVI using QR codes that utilizes the smartphone's camera [44]. QR codes intended to be used by PVI are installed on the floor.