Wednesday, April 02, 2014
Accuracy tests of Trackman
By our good buddy Alan and friends, we see some mostly positive results, with some hiccups:
The individual points are plotted in blue, and the dashed curve is a line corresponding to equality between the two measurements. With some exceptions, the data are tightly bunched about this line, indicating substantial agreement.
But there are exceptions, indicated by the 6 points (out of 94 total) for which the Trackman spin is well below the video spin. Inspection of the raw Trackman data, which are not generally available to Trackman users, indicates that this effect is almost surely an artifact of how the raw data are processed.
Indeed, five of the six points differ from the video spin by exactly a factor of two and the other by exactly a factor of five. The red points on the figure result from multiplying the points that are obviously wrong by the appropriate factor of two or five, and these corrected points fall right on the line.
It is interesting to note that each of the six points is a line drive; no fly balls that we measured showed that effect. Given that pitched baseballs are nothing more than line drives going in the opposite direction, it would be well to keep this occasional problem in mind when using Trackman to measure the spin of a pitched baseball. ?
I don't think it's a surprise to know that the Trackman folks highly respect Alan, so, it will be interesting to see their response.
***
As an aside: where Alan is now, "retired", but still the seeker of truth, is my post-career goal.
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