Environment

Categories

3.3 Environmental preparation

Space of Room

Gait analysis requires space for the subject to walk in and to maintain a reasonable camera-to-subject distance. Of course, larger space without any obstruction would be better. 

There are three factors to be considered, length of walkway, calibrated volume and distance from calibrated volume to camera location.

1. The length of walkway depends on the population and speed of gait. For normal gait of adults, about 10 m of walkway is needed for the sampling of gait with constant velocity excluding accelerating or decelerating phase of gait. For children or pathologic gait patients shorter walkway can be used without any problem.

2. The calibrated volume is the volume of sampling for analysis. The calibrated volume should encompass the range of movement of all markers during the motion we are to analyze. Usually, at least 1.5 gait cycle (about 2m along the walkway for normal adults and less for children or patients with pathologic gait) should be included. About 1m or more would be good for the width of the volume. For the height of the volume, it should be at least 2m if whole body (including head) is interested and at least 1.2 m if for lower body only.

3. There should be some distance between the calibrated volume and the locations of cameras. This distance depends on the characteristics of cameras used.

For example, a 4.8 mm lens on a 1/2 camera provides a 69 degree angle on your lens. This calculates out to a 1 meter field of view for every .73 meters of distance of the subject to the camera. Hence the following can be used for a 4.8 mm lens

A 6.0 mm lens provides an angle of 58 degrees or a D= .902 Field of View 8.0 mm lens provides an angle of 44 degrees or a D= 1.25 field of view (from Dan India posting to CGA-L).

But because cameras are located a little diagonally to the walkway rather just perpendicular, more calibrated volume is sampled with less distance. And APAS/Gait based on real video, which enables manual correction of merging effect, can encompass more volume of calibration with shorter distance than other infrared based systems.

Light control

APAS/Gait does not depend so much on light control as usual infrared based system. It will be enough to shield the direct daylight from the windows. There is no need to control any lights.

This page was last modified on 12/07/2008 at 22:47 PST. Copyright � 1994 - 2002, all rights reserved, Ariel Dynamics Inc. Please send your comments or feedback to webmaster@arielnet.com or proceed to our feedback form. This page has been accessed many times since Dec 12, 2002. Our privacy policy is here.