16 Reply by Chas Tennis (edited by Chas Tennis 2012-09-30 20:28:21)

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jontyc wrote:

.................Did you end up getting Stosur's kick serve? smile

I'm contemplating going down the 3M retroreflective tape route, on top of 20mm spheres, to measure 10-15 places on a golfer (and one on the club head) via multiple cameras. ..................................................

Idea is to add one or more IR LEDs to PS3 Eye cameras and replace their IR filter with a visible light filter and work solely in the IR domain (I'm only after tracking information leading to data, not image). No idea at this stage how many IR LEDs will be needed to work outside or even if I've have enough power via USB to drive them all.

I do have a Casio FC100 but will go with the PS3 Eyes because they are cheap, they can be synced and give me shutter control. They can do 125fps but only at 320x240 which I'm thinking will give insufficient accuracy, so I'll stick to 60fps with 4 times the pixels. Frustratingly the FC100 doesn't have shutter control in its high-speed modes, unlike your FH100. Unfortunately the PS3 Eye cameras also have a rolling shutter which give noticeable distortion at golf swing velocities.

Stosur's kick serve

Update:  9/30/2012 - https://vimeo.com/40449544

I have other serve videos and can easily see internal shoulder rotation but I'm having trouble clearly seeing pronation.......the term 'pronation' is badly misused in tennis discussions - outside its proper definition. My current high speed video objective is to understand the timing of pronation relative to the main driver of the serve - internal shoulder rotation.  A fun project.

Search "motion capture" and see what these professional motion capture systems are using.  I believe that many retro reflective systems use rings of many LEDs on each camera with the camera lens in the center (optimal for the retro-reflection).  I believe that nearly all motion capture systems work indoors where the lighting can be controlled.  One had some outdoor capability. See Vicon link.  Maybe there was another. ?

I posted a thread for information on high speed video cameras and considerations. 

http://www.kinovea.org/en/forum/viewtopic.php?id=435

See Reply #1 for frame rate, shutter speed and Jello Effect (especially the golf examples)

See Reply #11 for a discussion of the very large difference in illumination levels - 100X - between indoor lighting and outdoor sunlight.

See reply #12 for more on the Jello Effect.

Look at my Vimeo video tests for LED source strength and also Jello Effect tests.  These tests are simplified simulations of actual high speed video conditions.  I'd rather be able to calculate Jello Effect under all conditions, camera settings, etc. but don't know how so I simulate them. These tests are very easy to do and tell you if sources are bright enough or if you need to worry about the Jello Effect.  (Unless you test, I'd worry.)

For example, this bar on a disc is rotating at about twice the speed of a 100 MPH golf swing viewed from the side and filling the frame.
http://vimeo.com/21529497
Using the Casio FH100 at 240fps, the bend in a golf club would be about 1/2 the bend seen in the video simulation.

Recommend doing calculations in Reply #1 for your PS3 for various frame rates and shutter speeds.  I assumed a 100 MPH golf club head speed for my examples. Set up some Jello Effect tests and test for your marker and lighting approach.

17 Reply by jontyc (edited by jontyc 2012-01-27 00:31:25)

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Chas Tennis wrote:

Search "motion capture" and see what these professional motion capture systems are using.  I believe that many retro reflective systems use rings of many LEDs on each camera with the camera lens in the center (optimal for the retro-reflection).

That's correct. The great thing about golf swing is that it's done on the spot, allowing closer camera positioning than what professional systems have to cater for. I'm hoping fewer LEDs will be sufficient.

The PS3 Eye cameras may well turn out to be insufficient and I may have to look into something with more fps, more resolution and a global shutter. At least prices are heading in my direction considering this is only a hobby for my personal swing.

Chas Tennis wrote:

I have other serve videos and can easily see internal shoulder rotation but I'm having trouble clearly seeing pronation.......the term 'pronation' is badly misused in tennis discussions - outside its proper definition. My current high speed video objective is to understand the timing of pronation relative to the main driver of the serve - internal shoulder rotation.  A fun project.

Coincidentally I only read a paper exactly about that the other day, being interested in the effect of forearm pronation on proximal-distal sequencing in the golf swing.

Here are some graphs you may find interesting if you haven't also read the paper:

http://i43.tinypic.com/dbr6ab.jpg
http://i44.tinypic.com/23sdxys.jpg

But note the paper is from the year 2000.

18 Reply by Chas Tennis

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That is exactly the information that I have been looking for!!

It is easy to see why I could not see forearm pronation at the same time as internal shoulder rotation(ISR).  Forearm pronation occurs while the elbow is still bent before the semi-straight arm position, internal shoulder rotation and impact.  Forearm pronation is difficult to see without well placed markers on the wrist and elbow. 

Thanks!

Some considerations for your golf set up-

Standard Approach:  For most golf swing analysis the Casio FH100 and earlier Casio cameras with manual shutter speed control (at about 240 fps) do a completely adequate job in outdoor light.  For tennis I have put black tape markers near my elbow bones to indicate upper arm rotation (internal shoulder rotation).  One early test indicated that Kinovea could track the black tape on my arm.   I did not pursue farther to optimize the tracking. Other convenient markers might be, for example, circles on dark background clothes or sweat bands with bright circles. For golf swing tracking in strong sunlight illumination this seems like a feasible tracking approach.   

Retro Reflective Tape & Illumination: To illuminate the few square meters of a golf swing in direct sunlight or with overcast skies seems very difficult.   To send a strong beam onto a much smaller area might be feasible.  ?  Using a very large mirror behind the camera lens to reflect the sunlight onto the golf swing might also work to illuminate retro reflective tape.  But a large mirror is a cumbersome set-up and the reflection would disturb the golfer.

LEDs on the Golfer:  On an overcast day directional LEDs placed on the golfer and club with output beams aligned toward the camera lens should be visible in the video.  In direct sunlight?   But if the LEDs change pointing angle too much the signal will go down or be lost.  Directional LEDs worked for the bicycle application indoors. Probably also workeable for runners and other applications where alignment is maintained. (For tennis applications where everything turns this alignment issue seemed a big problem to me.) Diffuse LED's don't have as much sensitivity to alignment but they will be much less bright for outdoor applications.   

Camera Lens:  For accuracy avoid extremely wide angle lens set-ups where the magnification at the center of the image is considerably greater than toward the edges.  The more telephoto lens with the camera farther from the object the more 'flat' and accurate the image will be.

19 Reply by Greg G (edited by Greg G 2013-02-18 01:08:08)

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Hello all!

Playing around with tracking markers that I printed out (from a Google image search).  Took video of my service motion.  They seem to work pretty well, as long as the camera can see them.  A lot of manual corrections done to the tracking, especially at areas of change in the background (light/dark).  But pretty useable overall!

[video]http://www.youtube.com/watch?v=UeO1irM0ujw[/video]

20 Reply by kevinjohnpatrick

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Greg, how did you superimpose a pro player over your image? As a teaching pro I'd like to know how. Thanks.

21 Reply by Greg G

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You open two videos in one window.  Then you just control the transparency of the overlay, and align the 2 videos as best as you can.