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Orientation Angles

Orientation angles are used in describing the attitude (orientation) of a rigid object that is rotating in the 3-D space. In golf, the orientation angles of the pelvis and thorax are often used in assessing the golfer's swing.

Orientation angles are essentially the three consecutive rotation angles used in rotating the rigid body from a reference attitude to the attitude of interest. Orientation angles are specific to the rotation sequence used. Figure 1 shows the three consecutive rotations used in describing the orientation of the pelvis. The rotation sequence used in this example is the 'rotation-lateral tilt-P/A tilt' sequence.

Pelvis OA

Figure 1. Orientation angles of the pelvis computed based on the rotation-lateral tilt-A/P tilt sequence. The hip line (HL) is used as the main axis of the pelvis. The first rotation (rotation) is about the vertical axis while the second rotation (R/L tilt) is about a horizontal axis perpendicular to the vertical plane that contains the HL. The third rotation is about the HL.

Initially, the pelvis is aligned with the X, Y, and Z-axis. The hip line (HL) is along the X-axis in the reference orientation. The first rotation (L/R rotation) is about the vertical axis (Z). With this, the HL rotatates from X to a new position on the horizontal plane (X1). The Y-axis also moves to a new position (Y1). The second rotation is about the Y1-axis and the HL rotates from X1 to X2, moving away from the horizontal plane. In other words, the first two rotations are used in moving the HL to the target position. The third rotation is about the X2-axis which causes the pelvis to rotate about the HL. These three rotations can be labeled as L/R rotation, lateral (R/L) tilt, and P/A tilt (the tilt about the HL). A left rotation, right tilt, or posterior tilt yields a positive orientation angle in this convention.

The orientation angles are sensitive to the rotation sequence used.