Technologies and techniques of location and navigation are advancing, allowing greater precision in locating people in complex and challenging conditions. These advances have attracted growing interest from the scientific community in using indoor positioning systems (IPSs) with a higher degree of precision and fast delivery time, for groups of people such as the visually impaired, to some extent improving their quality of life. Much research brings together various works that deal with the physical and logical approaches of IPSs to give the reader a more general view of the models. These surveys, however, need to be continuously revisited to update the literature on the features described. This paper presents an expansion of the range of technologies and methodologies for assisting the visually impaired in previous works, providing readers and researchers with a more recent version of what was done and the advantages and disadvantages of each approach to guide reviews and discussions about these topics. Finally, we discuss a series of considerations and future trends for the construction of indoor navigation and location systems for the visually impaired.

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This paper presents an indoor navigation wearable system based on visual markers recognition and ultrasonic obstacles perception used as an audio assistance for blind people. In this prototype, visual markers identify the points of interest in the environment; additionally this location status is enriched with information obtained in real time by other sensors. A map lists these points and indicates the distance and direction between closer points, building a virtual path. The blind users wear also glasses built with sensors like RGB camera, ultrasonic, magnetometer, gyroscope, and accelerometer enhancing the amount and quality of the available information. The user navigates freely in the prepared environment identifying the location markers. Based on the origin point information or the location point information and on the gyro sensor value the path to next marker (target) is calculated. To raise the perception of the environment, avoiding possible obstacles, it is used a couple of ultrasonic sensors. The audio assistance provided to the user makes use of an audio bank, with simple known instructions to indicate precisely the desired route and obstacles. Ten blind users tested and evaluated the system. The results showed rates of about 94.92% successful recognition of the markers using only 26 frames per second and 98.33% of ultrasonic obstacles perception disposed between 0.50 meters and 4.0 meters.

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