//

CSS Menu Buttons Css3Menu.com

VisTrak Installation VisTrak Eagle VisTrak SCX VisTrak EV VisTrak KX VisTrak LX Video Swing Capture Videos

 

Ball Spin Setup

Selecting the Ball Spin Detection method

There are currently 3 methods of ball spin detection:

1.

Spin calculated using balls without markings

The spin rate is then calculated from ball and club data.

Note that as long as the shot is reasonably straight,

the difference between measured and calculated ball spin is mostly marginal

2.

Using balls with spin dots on them

The spin rate is then measured

The advantage of using spin dot balls compared to using the ball logo or line,

is that you don't have to bend down to align the ball logo or line to the camera.

3.

Using balls with a line or strong black logo

This method is mostly very accurate but requires the user to bend down to align the ball logo or line to the camera.

4.

Ball dimple method

(not yet available)

i.e. using balls without any markings and relying on ball dimple patterns to determine spin rate.

This method is currently in development but we cannot guarantee when this development will be completed.


VisTrak SCX Ball Spin Detection

If you prefer measured ball spin instead of calculated ball spin, then spin dot balls will be required as well as additional lighting

If not using the narrow beam IR lights, this will require that the system have to feature additional lighting.

i.e. 8 LED track lights instead the standard 4 track lights

The above image (from a customer shot video) shows the issue with longer exposure times

and out of focus lenses when attempting to detect ball spin dot markings.

Exposure times need to be under 150 us to reduce motion blur caused by the ball traveling at high speeds.

Nether-the-less, if increasing the Ball Spot GS (gray scale) to 200,

then even out of focus and blurry ball dots can be detected.

Today's CP version also features improved ball spin frame detection by attempting to find 2 adjacent

ball images that have at least 3 dots on them instead of just 2.

Note that only well defined and spaced spin dot balls or balls with a strong logo can be used ( as shown above).

Note that camera exposure time (i.e. shutter speed) has to be set at or below 100 micro seconds and frame set to 1500 fps.

Lighting requirements in order to measure ball spin with the ceiling mounted SCX

Measured ball spin requires clear non-blurry images of the ball in flight so that ball markings can be clearly seen.

This can only be accomplished by reducing the camera's exposure time to below 100 micro-seconds,

which in turn requires strong lighting.

If not using the narrow beam IR lights (as featured in the SCX IR),

the system will have to feature additional lighting.

i.e. 8 LED track lights instead the standard 4 track lights.

GSA Golf Hi-intensity CM Vision IR narrow beam lights

-

When using the CM Vision narrow beam angle lights, camera shutter speeds can be reduced to well under 100 micro seconds.

This will ensure that ball motion blur is at a minimum and ball markings are clearly visible

Track Lighting

4 hi-power LED zoom-able track light system with 800 Lumens per light with track

Price $199


 

Note that the VisTrak systems require that the camera shutter speed has to be at or below 100 micro seconds

if ball spin is to be measured and not calculated.

Note that the "Ball line/Spot GS" (Gray Scale) may ( depending on your lighting )

have to be adjusted up or down in order to detect the ball spin dot or ball logo.

New Ball Spin detection using the ball logo

for overhead SCX and Eagle systems

You can now select the option "Spin line / Logo on ball" to measure ball spin for overhead camera systems (i.e. SCX and Eagle).

As the logo will not always be visible in the frames, the system now automatically scans for 2 adjacent fames showing the ball logo

in all the 16 ball speed frames.


VisTrak EVi / LX2

Ball Spin Detection from the Side camera

Note that no additional lighting is required with the LX2 and EVi (near) systems as the light source is very close to the ball

The default camera exposure time for the LX2 Vcam is just 50 micro seconds

Using the ball logo or line

When the EVi or LX Vcam is placed close to the ball (i.e within 12 to 16 inches),

the camera detects ball spin rate using either the ball logo or ball spin dots.

Using balls with spin dots on them

The Vcam with EVi and LX systems view the ball from the side.

Rotation - when using spin dot balls - is calculated around the center of the ball between frames

Note that the "Ball line/Spot GS" (Gray Scale) may have to be adjusted up or down in order to detect the spin dot or ball logo/line.

EV Ball Spin Detection from the overhead camera

Ball spin can also be measured from the EV overhead camera

Rotation and spin axis is calculated by comparing x and y spin dot deviation positions between frames

Ball spin for Putts

Measured ball spin when putting is done without the requirement to use ball markings.

 


Spin Dot / Ball Logo Detection issues

In order to detect the spin dots on the ball or ball logos, the images should be sharp and clear.

In order to achieve this, the camera exposure time has to be fast (i.e. around 100 us) with bright lighting.

If the exposure time is too long (i.e. 300 us plus) then image blur will occur and the dots will appear faint.

Adjusting the "Ball Line/Spot GS" (gray scale) to a very high level (i.e. 200) can help though.

Click above to read more about ball spin detectionn theory...


Ball Spin rate accuracy verification method

In order to verify the ball spin rate accuracy of the VisTrak SCX system,

we'll need a solid reference. i.e. frames of a spinning ball with a known spin rate.

To do this, we used a variable speed DC motor with a marked golf ball on it.

First we'd have to accurately measure the spin rate of the motor.

This was done by using a laser tachometer and a black rubber disc with a white strip on it attached to the motor's spindle.

In this case, the reading was 2488 rpm

Note that you can't use a tachometer with a golf ball because laser tachometers only read single white markings on a dark background.

We then replaced the black rubber disc with a marked golf ball on the motor's spindle

and setup the VisTrak camera to capture 32 frames of the spinning ball.

We then compared the spin rate readings from the VisTrak SCX cameras with the tachometer reading.

The small discrepancy was rectified by increasing the spin rate adjust factor from 100 to 109 percent

Virtual spin dots for SCX testers

The virtual spin dot mode is basically just a tool used by GSAgolf to simulate ball markings on the ball

and to view the resulting measured back and side spin rate

Virtual spin dots are used to test the spin detection method.

In the camera panel, Select a frame with a ball shown in it.

Select spin dot or logo on ball spin method.

Press the V key on your keyboard to go to Virtual Dot Mode

Use arrow left/right/up/ down keyboard keys to move dots around on the ball

The dots can be moved around anywhere on the ball image

and the resulting back and side spin rates - based on their co-ordinates - will be automatically shown.

Ball Spin Test Videos

For those that are interested, I've made a collection of ball spin videos using line/logo marked balls, QED marked balls and Rapsodo marked balls.

Click the above image to download the videos (32 MB compressed)

All 32 frame videos were captured at 1500 fps with the ball spinning at 2488 rpm.

Each ball type consists of 4 different viewing angles: Top, Side, Tilted Top and Tilted side.

To try the videos, copy the video number from the downloaded sub folder into the C:\ GSAgolf folder on your PC.

Go to the Videos panels and select the video number and go to camera 1.

Select any frame and press the 1 key on your keyboard, then go to the next frame and press the 2 key.

Then click on the spin video box to re-calculate the spin rate from the 2 frames you have previously selected

GSA Golf use these ball spin videos to simulate various ball marking position scenarios to confirm the correct measured ball spin

Sample shot videos

Sample Video 3 is from an LX2 system (running at 1500 fps) showing the top and side views of the club striking the ball

and capturing ball spin from a ball logo or line on the ball

GSA Golf Control Panel Full version download

The full version VisTrak software can be used to evaluate the system with real time image processing

from sample shot videos sent to us frome customers.

Use the above download to install the full version Control Panel with sample shot videos.

Download includes SCX, EVi and LX2 sample shot videos

 

All camera products Club Tracking Camera Ball spin camera VisTrak systems LX Launch monitors Enclosures All products Software Business Installation and setup