Navigation Assistance for Visually Impaired (NAVI) refers to systems that are able to assist or guide people with vision loss, ranging from partially sighted to totally blind, by means of sound commands. In this paper, a new system for NAVI is presented based on visual and range information. Instead of using several sensors, we choose one device, a consumer RGB-D camera and take advantage of both range and visual information. In particular, the main contribution is the combination of depth information with image intensities resulting in the robust expansion of the range-based floor segmentation. On the one hand, depth information, which is reliable but limited to a short range, is enhanced with the long-range visual information. On the other hand, the difficult and prone to error image processing is eased and improved with depth information. The proposed system detects and classifies the main structural elements of the scene providing the user with obstacle-free paths in order to navigate safely across unknown scenarios. The proposed system has been tested on a wide variety of scenarios and datasets, giving successful results and showing that the system is robust and works in challenging indoor environments.

In this study, we present a calibration technique that is valid for all single-viewpoint catadioptric cameras. We are able to represent the projection of 3D points on a catadioptric image linearly with a 6×10 projection matrix, which uses lifted coordinates for image and 3D points. This projection matrix can be computed from 3D-2D correspondences (minimum 20 points distributed in three different planes). We show how to decompose it to obtain intrinsic and extrinsic parameters. Moreover, we use this parameter estimation followed by a non-linear optimization to calibrate various types of cameras. Our results are based on the sphere camera model which considers that every central catadioptric system can be modeled using two projections, one from 3D points to a unitary sphere and then a perspective projection from the sphere to the image plane. We test

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Omnidirectional cameras are becoming increasingly popular in computer vision and robotics. Camera calibration is a step before performing any task involving metric scene measurement, required in nearly all robotics tasks. In recent years many different methods to calibrate central omnidirectional cameras have been developed, based on different camera models and often limited to a specific mirror shape. In this paper we review the existing methods designed to calibrate any central omnivision system and analyze their advantages and drawbacks doing a deep comparison using simulated and real data. We choose methods available as OpenSource and which do not require a complex pattern or scene. The evaluation protocol of calibration accuracy also considers 3D metric reconstruction combining omnidirectional images. Comparative results are shown and discussed in detail.

Abstract-In this work we integrate the Spherical Camera Model for catadioptric systems in a Visual-SLAM application. The Spherical Camera Model is a projection model that unifies central catadioptric and conventional cameras. To integrate this model into the Extended Kalman Filter-based SLAM we require to linearize the direct and the inverse projection. We have performed an initial experimentation with omnidirectional and conventional real sequences including challenging trajectories. The results confirm that the omnidirectional camera gives much better orientation accuracy improving the estimated camera trajectory.