Technologies for visual localization and augmented reality in smart cities

The widespread diffusion of smart devices, such as smartphones and tablets, and the new emerging trend of wearable devices, such as smart glasses and smart watches, has pushed forward the development of applications where the user can interact relying on his or her position and field of view. In this way, users can also receive additional information in augmented reality, that is, seeing the information through the smart device, overlaid on top of the real scene. The GPS or the compass can be used to localize the user when augmented reality has to be provided with scenes of large size, for instance, squares or large buildings. However, when augmented reality has to be offered for enriching the view of small objects or small details of larger objects, for instance, statues, paintings, or epigraphs, a more precise positioning is needed. Visual object recognition and tracking technologies offer very detailed and fine-grained positioning capabilities. This chapter discusses the techniques enabling a precise positioning of the user and the subsequent experience in augmented reality, focusing on algorithms for image matching and homography estimation between the images seen by smart devices and images representing objects of interest.