Ball spin camera using IR LEDs
Add-on to VisTrak Eagle with Vcam
If you already have a third camera, then you'll just require the LED lights.
The S cam is a hi-resolution camera that - when used in conjunction with the hi-res Vcam camera -
can calculate spin rate from the two images.
VisTrak Vcam B
Add-on to the VisTrak Eagle for LA and Spin detection
Contact us to purchase
The Vcam B is the same is a Vcam plus an Spin cam but mounted in a carry case
Measuring ball spin using the ball's logo.
The Vcam B captures 3 frames with the two floor mounted cameras.
Frame 1: the ball at launch position (captured when the VisTrak camera detects a ball on the mat).
Frame 2: the ball in flight after the trigger delay
Frame 3: the ball in flight after the base trigger delay plus an additional Cam1 to Cam2 delay
Cam 1 to Cam 2 trigger delay
The trigger delay difference between camera 1 and camera 2 is used to calculate the ball spin
It is set independently from the base trigger.
Both cameras have the same base trigger delay - in order that the ball in flight is captured in the FOV of the cameras - but camera 2 has this additional delay added to it.
This difference in trigger delay time is used as the time taken for the ball to rotate in the ball spin images and directly effects the spin calculations.
Most will probably not want to use specially marked balls so we have developed the Bcam system to use the standard ball logo on the ball to measure ball spin and spin axis.
New logo matching end detection.
An issue with measuring ball spin using the ball's logo is that the correct matching ends of the logo must be detected in order to correctly measure the amount of rotation within the time frame..
i.e. if one end of the logo is found in image 1 then that same end has to found in image 2. Failing to do this can result in very different ball spin rate measurements.
The above two images show a ball spinning at a rate of 8321 rpm. We know this because the amount of rotation within the 1 ms frame delay was 149.78 degrees.
And we only know the correct amount of rotation because the Letter "C" in the Calloway logo has been detected correctly in both frames. This is shown by the two red cross hairs over the letter "C".
Without this new "Matching logo end detection" feature, the CP image processing may well get the ends mixed up and then a totally different amount of rotation will be measured
(i.e. 30.22 degrees here) and thus a totally different and false ball spin rate will be calculated. (Note that the two sets of images are from the same shot.)
As can be seen from the above two images, the letter "C" in the Calloway logo has not been detected in image 2 (i.e. there's a green cross hair on the "C" instead of a red cross hair).
And thus a false spin rate measurement was calculated (i.e. 1678 rpm instead of the real 8321 rpm).
It should be noted that not all ball logos have a dominant end and thus it may be required to use a black magic marker or black ink pen to accent one end of the logo.
Note that measuring ball spin using the logo (or any marked balls like those with About Golf systems) is the only way a camera method of ball spin detection is able to do this in real time. i.e. without a long 2 to 4 second or so lag time (SkyTrak / GC2 etc).
While radar systems (Trackman, FlightScope etc) require metallic dots be applied to the ball and the ball be placed with the dot facing upwards.
VisTrak Vcam B setup
Side Spin and spin axis detection
Note that in reality a ball cannot have both back spin and side spin at the same time. In reality a ball has only spin and spin axis.
Never-the-less, a theoretical side spin rate can be measured by the amount of horizontal rotation within a certain time period.
And a back spin rate can be measured by the amount of vertical rotation within a certain time period.
Side spin theory
Side spin is imparted on the ball by the club face striking the ball with a relative-to-club-path face angle that is not square - i.e. open or closed.
This open or closed club face relative to the club path will cause the ball's backspin rotation axis to shift off center.
The above image shows ball spin without any side spin and 0 degree spin axis. The red line represents a line or logo on the ball.
If the Bcam is overhead mounted (Top View), then the line will only move backwards in each frame if there is no side spin and the line will have the same angle in each frame.
This backward movement is vertical rotation and is used to measure the back spin.
If the Bcam is mounted at floor level (for a side view) and there is no side spin, the red line will continue to rotate around the initial center of rotation
and the amount of rotation within a certain time period is used to calculate the back spin rate in rpm.
The "ref frame" is a frame of the stationary ball on the ground or tee before being struck.
The above image shows ball spin with side spin.
If the Bcam is overhead mounted (Top View), then the line angle will have changed from the initial image of the ball on the ground or tee
to a different angle after launch. This change in angle within a certain time frame is used to calculate the amount of side spin in rpm.
If the Bcam is side mounted (side view), then the line will be seen as rotating around a different axis compared to the initial axis the line was on when on the ground or tee.
We use this shift in spin axis to then calculate the side spin rotation in rpm.
Spin axis theory
Note that spin axis is never always on one plane. i.e. spin axis can have both a vertical and horizontal component to it. Thus spin axis is a 3D value.
So when you see a launch monitor displaying a spin axis of 4 degrees left or right, it is not known whether this value is on the vertical or horizontal plane.
As the real spin axis value can only described by a mathematical 3D vector - which most average golfers will have difficulty comprehending - it is simplified by reducing it to just the one plane.
Just like side spin: it's not real but we can at least grasp its meaning.
Bcam side view images
The above shows real balls - viewed from the side - with a back spin rotation and rotation axis shift.
Side spin can then be converted to spin axis.
Note that both the single camera Bcam and dual camera Bcam Pro are both using reference frames now. i.e. images of the ball on the ground or tee are automatically captured.
Bcam overhead view images
The above images are from the Bcam when mounted overhead.
Bcam overhead mounted images
Left: frame 2 of full shot with 3 wood - Right: frame 1 of ball on mat hitting position
Left: frame 2 of open faced 3 wood. Right: Composite of frames 1 and 2.
Bcam side mounted images
Left: 9 iron shot using spin dots on ball ---------------------- Right: White head driver using line marking on ball