Phil Cheetham on 3-D versus 2-D

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lia41985

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TPI Instructor - Gord Workum just wrote an article explaining in simple terms why 3D motion capture is better than 2D video. Gord stated that 3D quantifies the motion of the golf swing objectively; this is true, but one might immediately think “But wait, I can measure distance and angles on a 2D video screen by drawing lines.” Yes, you can but there is a good possibility your result will be wrong and potentially a lot wrong.In response to that idea, this article explains why 3D motion capture can be pictured as videoing the golfer with an infinite number of 2D cameras and not only that but these imaginary cameras actually follow every part of the golfer’s body throughout the entire swing.

For example to measure the true wrist set/release angle accurately with a 2D camera you would have to position the camera perpendicular to a plane along the forearm and club shaft and the camera would have to remain in that perpendicular relationship to the arm/club throughout the entire swing; it would have to follow the arm/club. If the camera is not perpendicular to this plane then the angle being measured can be totally wrong. For example, when you position a camera at hand height looking at the front of the golfer, the wrist set angle is probably never perpendicular to this camera. So drawing a line along the arm and the shaft at the top of backswing and using a video analysis system to tell you what this angle is is completely wrong. The angle could be tens of degrees off!


However using 3D to measure these angles is easy and automatic! Capturing the data may take a little time for setup but once you have the 3D data you can make almost any calculation you want; especially with AMM3D and TPI 3D.


How does it work? Let’s simplify a little and imagine the golfer as a stick figure with each joint the beginning and end of each stick. 3D allows us to know exactly where these joints are at each instance in the swing in terms of three basic numbers; the X, Y and Z coordinate values of each joint. This also allows the computer to draw the 3D stick figure (or TPI Robot) on the screen at every instance.


Let’s go back to the example of the wrist angle. If we know the X, Y and Z coordinates of the elbow, wrist and bottom of the grip then we can draw a line (a.k.a. vector) between each point and use trigonometry to calculate the angle between the lines, and since we are using the 3D coordinates to draw these lines then the angle will always be exactly correct; as if we were looking at it with a perpendicular 2D camera that followed the arm throughout the swing.


So in summary with a good 3D analysis system we can get accurate measurements of positions, angles and any point in the swing. In addition; since we know the time between 3D “pictures” we can also calculate speeds and accelerations of any body part or joint.
Link: My TPI (Titleist Performance Institute) - Your Source for Golf Fitness, Exercises and Health
 
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