Doubts on the accuracy of the horizontal launch angle

[davray666]

I have had doubts on the accuracy of the horizontal launch angle for some time and planed to measure it with a camera setup. But I found a much simpler method that works well enough.
The quoted accuracy of +/- 2 deg is not even close. For those of us that primarily use the device for skill tuning it's not a big problem if you do this.
Assuming you are hitting in to a screen or somewhat firm surface. Mark the target line on the screen with painter tape from top to bottom.Measure the distance from ball position to the screen point that you are mostly interested in. (in my case 30 deg vertical angle) and calculate separation for each degree and mark that with a piece of tape. (in my case it was 6cm / degree and I marked 4 degrees in each direction. Now when you tune your short irons and wedges you will be able to see what the horizontal launch angle was by simply observing where the ball hits the screen. If the result shows a bias toward ether direction you can fine tune the unit position. Assuming the ball speed and spin is accurately measured (based on feel I would say it is) you will now be able to manually correct the observed ball trajectory in your mind.
I have frequently observed errors that are up to +/- 8 degrees wrong and in some rare cases a bit worse than that. Problem is that it's sometimes spot on and other times way off in either direction. My feeling is that the higher VL angle the less accurate HL angle.
The real problem will come when we start playing simulator golf with the unit. There is no way to correct the shot in the game. Imagine the discussion when you play a cash prize tournament on E6 cloud and your final approach shot ends up in the water instead of the green just because the of ST unit measuring error.
With that said. The unit has been fantastic so far and my skills have improved a lot during the 3 months I have had it. But in order to get the full benefit you need to understand how it works and compensate for the errors it produces. So with all that I know now, would I still buy one? I most definitely would, but I have not used it with a simulator yet.

[SkyTrak_Seth]

Are you using clean/new'ish white golf balls? +/- 8 degrees is way off. There has to be something going on. Is the unit on or at least level with the mat?

[davray666]

I have 16 balls in the hitting bay. A mix of Z-star XV, TM lethal and proV1. They where new a few 100 shots ago and have never been used outside of the indoor hitting bay.
But I would not go as far as to say they are 100% white and clean. I would be happy to take that in to consideration but it would help a lot if Skytrak could tell us what is OK and what is not by showing a few example images of balls. The term "clean" is very subjective. Another interesting point is if it helps to place the logo and other markings in any special way? For better spin measurement I think it has been said that there should be a mark facing the camera, but what about horizontal launch angle considerations? I never bothered to check if the error shot was related to any of the balls. I will check that next time. I will also run a clean new ball against a very dirty one to see if can spot any difference.

[davray666]

Sorry forgot to address the alignment question. The unit is leveled with a precision level standing on a surface that is leveled with the hitting surface. The leveled unit stand is separated from the hitting/stance mat. So there is no risk of any movement.

[davray666]

Here are a few images of the setup. I also did a few test shots with the balls you see in the picture. The Srixon ball being the good one and the Titleist one with the personal logo being the bad one. Personal logo was always placed for assumed maximum damage e.g. pointing up. Had to do 10 shots each before I got an error that was outside of spec. Actual 1 degree left, measured 6 degree left. Surprisingly enough the error was produced with the Srixon ball.

[SkyTrak_Seth]

So....it's ok now?

By clean - I just mean I've been to places before where it looks like they rubbed the golf balls down with black shoe polish and then ran them through a meat grinder - they couldn't figure out why it wasn't reading correctly.

[davray666]

OK, in that case I would rate the balls I use as clean. No it's not OK. I would say the problem is as described previously.
The remark in the previous post "Actual 1 degree left, measured 6 degree left" means that the HLA was 1 degree left and the unit reported 6 degree left.
I ran some more tests where I removed the protection enclosure just in case it's somehow blocking the line laser. The result is same as with the enclosure.
I also did a 2h driver session today and the out of spec errors are not as frequent as with the high vertical launch angle shots but they do happen.
When doing iron shots from the deck, ball placement is random, but when I do driver shots I have developed a habit of always turning the logo towards the Skytrak unit.
No idea if that might influence the horizontal LA measurement.

Pretty much all the shots I did that where described before where with a PW. My PW is typically never outside of +/- 2 degrees HLA. What I noticed with the driver today when I messed around with practicing alternate fades and draws is that errors increase dramatically if the HLA is above 6 or so degrees.
Would be great if someone else can run similar tests and report what they see.

[SkyTrak_Seth]

I guess maybe I misunderstood. What I thought you were saying is that the Srixon ball was new and the Titleist was old and beat up. (also wasn't sure about the maximum damage logo facing up part). I thought you said that out of 20 shots, you had 1 side angle misread - that doesn't sound completely terrible to me. I mean, obviously we would love to be 100% perfect, but we aren't - in fact, no launch monitor is perfect every time, not even Trackman. However, in a controlled environment like you are in, I would still expect the results to be better. Some things that 'could' have produced that misread are:
- Ball not perfectly on the laser dot (I'm talking distance from the unit, not front to back
- Ball on dot but not solid hit (too low, too slow, etc)
- Something else interfering in the image (hosel reflection?)

If high vertical shots are causing issues, you could try scooting the ball a little ahead of the red dot (to help get them in the picture given the much slower ball speeds) Just a suggestion, maybe worth a try.

Lastly, extreme side angle shots will, in fact, have an affect on the software's ability to analyze the spin. For instance, a very strong pull will have each subsequent image farther from the camera, thus making it harder for the software to track. This is unfortunately just a limitation of photometric technology.

[davray666]

First of all, thanks for the feedback. Yes I had to do 20 shots until I got 1 out of the specified +/-2 degrees. But it could just as well have been 5 out of 20. The error is very random.
As far as I am concerned as long as you are aware of it and have some way to gaze the direction the practice session becomes much more productive since the difficult to estimate data like spin and speed seams to be accurate.
The maximum damage logo facing up was related to how I guessed that the measurement is done. E.g. you don't want any dark markings on the ball to be positioned at the top or bottom of the ball edge as seen from the unit.
I always place the ball on the position laser dot for all shots that will end up below 35 degree VLA, For the wedge shots that will go higher I place the ball appr. 4" forward.
So in summary the way i am using it i am still very happy with the way it works now and it is a huge help.
I will probably revisit he topic once I try playing simulator games. In that case it will probably be to discuss the need to adjust/correct data in the game, when required in order to compensate for obvious measurement errors.

"Lastly, extreme side angle shots will, in fact, have an affect on the software's ability to analyze the spin. For instance, a very strong pull will have each subsequent image farther from the camera, thus making it harder for the software to track. This is unfortunately just a limitation of photometric technology."

Yeah I did not mention that because I did not think that was worth complaining about. I messed around with hooks/draws and fades/slices to see how i can control them. If you do a strong fade and start the ball 10 - 15 degrees left to have it end up at the target line you will see some interesting shot data. At one point I got 208MPH ball speed and some interesting spin numbers. (I have never achieved real ball speed above 165 MPH)
But considering that a shot like that would be totally useless on the golf course I did not think much of it. If you are one of those slicers that starts the ball way left just because you have no choice then you will have to fix your swing before you can use the Skytrak. Or maybe you should buy a Skytrak and practice so you get rid of that slice:-)

[Bubba22]

The horizontal azumuth is an issue with all side mounted camera based launch monitors even the GC2. A lot of the intolerances come from th camera picture quality, camera alignment and unit alignment. I think this measurement is the weakest part of these type of units. Aligning the unit perfect will help improve this but beyond that it is what it is. Out of curiosity davray, did you use th laser alignment assist and if so, how do you use it?

[davray666]

Hi Bubba,
I did use the laser alignment feature but kind of gave up on it. The problem is that the laser light shines thru the hitting surface "grass" and disperses. So it's difficult to get a good reading. I could have placed something else on top and used that but I am kind of skeptical to the accuracy of the laser to start with so I used the housing as reference to do the alignment instead. Then after hitting a bunch of shots I determined statistically by observing the actual HLA what the error was. As it turned out the housing is aligned to the unit measuring device.
My Skytrak unit is only used in the garage so you could say It's a fixed installation. For those that use it on the range I guess the dual laser alignment could be useful, but it is to much work to get it right since you need a leveled Skytrak to shine both lasers on a leveled hitting surface that is made of a material that does not disperse the laser dots.
I had plans to build a "range level platform" that has a bubble level with a built in laser attached to it and do some tests on the driving range. But I have not had tome to do that yet. The driving range has 2 bays with Trackman and a bunch of bays with Pro tracer, so it would be an interesting test.

[keithpbz]

I built a leveling platform for about $5 and use a digital angle finder to level everything to with 1/10 of a degree. My golf room has everything squared off the wall and draw square lines off wall on the floor to align the skytrak. I have never had an issue with the launch angles. I am kind of a range rat and hit alot of balls and play 20-30 rounds of tournament golf a year. If it feels like a push when I hit it that's how it shows up. And I've only had about 3 or 4 shots that didn't register. I pre ordered this and have hit thousands of shots on it.

[davray666]

keithpbz so if we restrict the discussion to horizontal launch angle only. Not having any issues would imply that your unit is spot on all the time. Is that the case?
if not what kind of accuracy in degrees would you consider is "no issue"?
Did you use "feel" as the only way to measure the actual result?
Not sure why you mentioned that the unit has only missed a few shots. That's not being questioned here. I have also done a few thousand shots and can't remember if the unit ever missed a shot. So that part is very robust.

[keithpbz]

I have a sheet in front of my net to save the balls from getting so beat up on the net. I had a black line painted vertically directly in line with the target line of the lasers. I set a iPhone up for a down the line shot and used the video recorder. I have a limited distance the ball flies, only about 8' or so. I'd have to measure to know for sure. If the ball missed the line in either direction the skytrak would show it the same in horizontal launch angle. It's been a few weeks since I did it but I think about 3* was the highest skytrak showed it starting offline. ive hit on many launch monitors and remember a trackman session indoors last year that showed me hitting a 180 yard sand wedge. The guy laughed and just said to ignore that one. I don't plan on using it for simulation and only to work on distance control. I hit 10 shots with each club and ignore the highest and lowest ones and use the remaining 8 for an average.

[davray666]

I don't think there is much more to be said about this topic. In conclusion.
The Skytrak HLA is within the specified +/- 2 degrees most of the time and has occasional random deviations. You will see more errors for those shots that are not straight.
The higher the HLA the greater the error especially for pull shots.(e.g. if there is an error, because the HLA can still be spot on even for hard pull shots)
For those of us that mainly use it for practicing this is not a big problem since HLA is probably the least important parameter you need to fine tune in your swing. But it's always good to be aware of it.
So for me next up is to setup my high speed cameras and measure how accurate the VLA, speed and spin is. Since the golf season has just started I strongly doubt I will get it done before the winter is back forcing us to get back inside. For those that are interested I will post the results when/if I have any.