One goal for the DIY launch monitor has been to be able to accurately determine the spin rate of balls in 3 axes without requiring any registration marks or other modifications to the ball (as some launch monitors need).  The system now has some new processing artifact outputs and other refinements to spin analysis to confirm that the spin analysis is working.  

The main idea is that because this is currently a new, and relatively untested system, we want to be able to give developers (and players!) the tools they need to visually sanity-check the spin analysis.  One way to do that is to start by showing the two balls (an initial ball and a final ball that has undergone some spin) that were chosen for analysis. Then, take the spin angles that the system calculated for spin and apply them to the first ball and show how that looks.  If things are working correctly, the first ball image (to which the spin angles were applied) should look to a human just like the original second (target) ball.

Particularly, depending on the trace-logging level, the system can now show the for-comparison balls at the same, normalized reference angle to make it more of an apples-to-apples comparison.  Each image is pre-rotated so that both appear as they would if the image were seen in the center of the image, straight down the camera lens bore.  

For example, see the results of the spin analysis that the system chose for the highlighted balls in the first image below, where the results are shown in the three later images.  A ball with marks was used in this example, but that’s not necessary.

As shown above, it looks great!  The exact determined angles above were (X, Y, Z):  (4, 6, 64) degrees before being adjusted for azimuth and pan angles.  Again, the system doesn’t require any registration marks like this ball has, but using a ball with marks does help for these visual sanity checks.  Oddly, the marks can actually detract a bit from the analysis accuracy.

The little dots all over the images are the results of the proprietary fast 3D projection and un-projections that the system uses.  These ‘holes’ could be interpolated away like most rotation algorithms do, but that’s not necessary for accurate spin-angle analysis.  It could also chew up time and has other downsides.