A method executed by a computer includes applying a correction to an acceleration value of an object at an interval; calculating an initial speed of the object by assigning the corrected acceleration value in a period to a third relational expression that is obtained by transforming a first relational expression and a second relational expression so as to obtain an initial speed from the acceleration in the period and the interval, where the first relational expression is to obtain an object position from acceleration and an initial speed, and the second relational expression represents force applied to the object due to fluctuation of the center of gravity of the object as a motion equation of a spring model; and calculating coordinate values over a horizontal plane that indicates a center of gravity of the object by assigning the corrected acceleration value and the initial speed to the first relational expression.