Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Top view image sequence of a series of activities (the duration of walking, tidying the table, sitting on sofa, switching TV programs, leaving the room). Each image is selected in every two seconds. The gray level corresponds to the pixel value (darker is higher), each white dot shows the estimated position by Equation (2) at time t.
