A computer-implemented method for using a depth image to extract user behavior, comprising: receiving a depth image that specifies that a plurality of pixels correspond to a user; fitting a curve to a portion of the plurality of pixels corresponding to the user, wherein the fitted curve comprises a plurality of straight lines; determining, based on the fitted curve, information indicative of an angle of the user's body and information indicative of a curvature of the user's body; wherein the determining information indicative of an angle of the user's body comprises: determining an angle between a floor supporting the user and a straight line extending between endpoints of the fitted curve or an angle between a straight line segment of the fitted curve and the straight line extending between the endpoints of the fitted curve, wherein the determined angle is indicative of an angle of the user's body; and wherein the determining information indicative of a curvature of the user's body comprises: determining a length of a first straight line extending between endpoints of the fitted curve; determining a length of a second straight line extending orthogonally from the first straight line to a point of the fitted curve that is farthest away from the first straight line; and determining a ratio of the length of the first line to the length of the second line, wherein the ratio is indicative of the curvature of the user's body. receiving a depth image that specifies that a plurality of pixels correspond to a user; fitting a curve to a portion of the plurality of pixels corresponding to the user, wherein the fitted curve comprises a plurality of straight lines; determining, based on the fitted curve, information indicative of an angle of the user's body and information indicative of a curvature of the user's body; wherein the determining information indicative of an angle of the user's body comprises: determining an angle between a floor supporting the user and a straight line extending between endpoints of the fitted curve or an angle between a straight line segment of the fitted curve and the straight line extending between the endpoints of the fitted curve, wherein the determined angle is indicative of an angle of the user's body; and wherein the determining information indicative of a curvature of the user's body comprises: determining a length of a first straight line extending between endpoints of the fitted curve; determining a length of a second straight line extending orthogonally from the first straight line to a point of the fitted curve that is farthest away from the first straight line; and determining a ratio of the length of the first line to the length of the second line, wherein the ratio is indicative of the curvature of the user's body. determining an angle between a floor supporting the user and a straight line extending between endpoints of the fitted curve or an angle between a straight line segment of the fitted curve and the straight line extending between the endpoints of the fitted curve, wherein the determined angle is indicative of an angle of the user's body; and wherein the determining information indicative of a curvature of the user's body comprises: determining a length of a first straight line extending between endpoints of the fitted curve; determining a length of a second straight line extending orthogonally from the first straight line to a point of the fitted curve that is farthest away from the first straight line; and determining a ratio of the length of the first line to the length of the second line, wherein the ratio is indicative of the curvature of the user's body. determining a length of a first straight line extending between endpoints of the fitted curve; determining a length of a second straight line extending orthogonally from the first straight line to a point of the fitted curve that is farthest away from the first straight line; and determining a ratio of the length of the first line to the length of the second line, wherein the ratio is indicative of the curvature of the user's body.