The integration of several range cameras in a mobile platform is useful for applications in mobile robotics and autonomous vehicles that require a large field of view. This situation is increasingly interesting with the advent of low cost range cameras like those developed by Primesense. Calibrating such combination of sensors for any geometric configuration is a problem that has been recently solved through visual odometry (VO) and SLAM. However, this kind of solution is laborious to apply, requiring robust SLAM or VO in controlled environments. In this paper we propose a new uncomplicated technique for extrinsic calibration of range cameras that relies on finding and matching planes. The method that we present serves to calibrate two or more range cameras in an arbitrary configuration, requiring only to observe one plane from different viewpoints. The conditions to solve the problem are studied, and several practical examples are presented covering different geometric configurations, including an omnidirectional RGB-D sensor composed of 8 range cameras. The quality of this calibration is evaluated with several experiments that demonstrate an improvement of accuracy over design parameters, while providing a versatile solution that is extremely fast and easy to apply.

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Semantic segmentation of images is an important problem for mobile robotics and autonomous driving because it offers basic information which can be used for complex reasoning and safe navigation. Different solutions have been proposed for this problem along the last two decades, and a relevant increment on accuracy has been achieved recently with the application of deep neural networks for image segmentation. One of the main issues when comparing different neural networks architectures is how to select an appropriate metric to evaluate their accuracy. Furthermore, commonly employed evaluation metrics can display divergent outcomes, and thus it is not clear how to rank different image segmentation solutions. This paper proposes a new metric which accounts for both global and contour accuracy in a simple formulation to overcome the weaknesses of previous metrics. We show with several examples the suitability of our approach and present a comparative analysis of several commonly used metrics for semantic segmentation together with a statistical analysis of their correlation. Several network segmentation models are used for validation with virtual and real benchmark image sequences, showing that our metric captures information of the most commonly used metrics in a single scalar value.