Low-cost human motion capture system for postural analysis onboard ships Erica Nocerino a,b , Sebastiano Ackermann a , Silvio Del Pizzo a , Fabio Menna* a,c , Salvatore Troisi a a LTF - Dept. of Applied Sciences, “Parthenope” University of Naples (Italy), http://ltf.uniparthenope.it b Dept. of Naval Engineering, “Federico II” University of Naples (Italy) c 3DOM Research Group, FBK - Fondazione Bruno Kessler, Trento (Italy), http://3dom.fbk.eu ABSTRACT The study of human equilibrium, also known as postural stability, concerns different research sectors (medicine, kinesiology, biomechanics, robotics, sport) and is usually performed employing motion analysis techniques for recording human movements and posture. A wide range of techniques and methodologies has been developed, but the choice of instrumentations and sensors depends on the requirement of the specific application. Postural stability is a topic of great interest for the maritime community, since ship motions can make demanding and difficult the maintenance of the upright stance with hazardous consequences for the safety of people onboard. The need of capturing the motion of an individual standing on a ship during its daily service does not permit to employ optical systems commonly used for human motion analysis. These sensors are not designed for operating in disadvantageous environmental conditions (water, wetness, saltiness) and with not optimal lighting. The solution proposed in this study consists in a motion acquisition system that could be easily usable onboard ships. It makes use of two different methodologies: (I) motion capture with videogrammetry and (II) motion measurement with Inertial Measurement Unit (IMU). The developed image-based motion capture system, made up of three low-cost, light and compact video cameras, was validated against a commercial optical system and then used for testing the reliability of the inertial sensors. In this paper, the whole process of planning, designing, calibrating, and assessing the accuracy of the motion capture system is reported and discussed. Results from the laboratory tests and preliminary campaigns in the field are presented. Keywords: Videogrammetry, motion capture, IMU, low-cost instruments, human postural stability onboard ships 1. INTRODUCTION Human postural stability is a multidisciplinary topic of great interest for several sciences and disciplines, since it has a profound impact on several aspects of everyday life. How individuals maintain balance, employ correct and efficient postural strategies, are able to prevent falls and occurrence of severe injuries are aspects that relate to medicine and neurophysiology, biomechanics and robotics, as well as rehabilitation surgery, occupational safety, ergonomics and sport applications. The study of postural stability and human movements in general is performed by employing different measurement methodologies that differ according to the sensors used. These techniques can be roughly classified in direct measurement methods, based on mechanical, electromagnetic, acoustic, inertial trackers, and indirect optical (imaged- based) methods 1,2 . In the past, direct measurement techniques made use of goniometers, electrical potentiometers attached to body’s limbs to measure joint angles 3 . In the last decade, inertial sensors, often integrated with magnetic sensors or GPS receivers, have become quite common for motion capturing and measuring 2,4 . Image-based sensors are nowadays very popular in both human body modelling and movement analysis 1,2,5,6 . Among the wide range of existing methodologies and technologies, the choice of instrumentations and sensors depends on the requirements of the specific experimentation. For example, high accuracy is needed for medical applications, as in gait analysis of cerebral palsy patients 3 . In sport applications, high data acquisition rate is necessary for better understanding athlete movements and improving performances 4 . Character animation in film and game industries, virtual reality, video surveillance are further sectors where motion capture is required, but in these cases photorealism of the final 3D model is the principal aspect 1,2 . fmenna@fbk.eu , fabio.menna@uniparthenope.it ; phone +39 0461 314446; http://3dom.fbk.eu , http://ltf.uniparthenope.it