Force from Motion: Decoding Physical Sensation in a First Person Video

Hyun Soo Park, Jyh Jing Hwang, Jianbo Shi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

10 Scopus citations

Abstract

A first-person video can generate powerful physical sensations of action in an observer. In this paper, we focus on a problem of Force from Motion - decoding the sensation of 1) passive forces such as the gravity, 2) the physical scale of the motion (speed) and space, and 3) active forces exerted by the observer such as pedaling a bike or banking on a ski turn. The sensation of gravity can be observed in a natural image. We learn this image cue for predicting a gravity direction in a 2D image and integrate the prediction across images to estimate the 3D gravity direction using structure from motion. The sense of physical scale is revealed to us when the body is in a dynamically balanced state. We compute the unknown physical scale of 3D reconstructed camera motion by leveraging the torque equilibrium at a banked turn that relates the centripetal force, gravity, and the body leaning angle. The active force and torque governs 3D egomotion through the physics of rigid body dynamics. Using an inverse dynamics optimization, we directly minimize 2D reprojection error (in video) with respect to 3D world structure, active forces, and additional passive forces such as air drag and friction force. We use structure from motion with the physical scale and gravity direction as an initialization of our bundle adjustment for force estimation. Our method shows quantitatively equivalent reconstruction comparing to IMU measurements in terms of gravity and scale recovery and outperforms method based on 2D optical flow for an active action recognition task. We apply our method to first person videos of mountain biking, urban bike racing, skiing, speedflying with parachute, and wingsuit flying where inertial measurements are not accessible.

Original languageEnglish (US)
Title of host publicationProceedings - 29th IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2016
PublisherIEEE Computer Society
Pages3834-3842
Number of pages9
ISBN (Electronic)9781467388504
DOIs
StatePublished - Dec 9 2016
Event29th IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2016 - Las Vegas, United States
Duration: Jun 26 2016Jul 1 2016

Publication series

NameProceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition
Volume2016-December
ISSN (Print)1063-6919

Conference

Conference29th IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2016
CountryUnited States
CityLas Vegas
Period6/26/167/1/16

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