Welcome to Part 3 of our Golf Launch Monitor Guide, following on from our article on the data produced by launch monitors.
In this post we will look in detail at the different types of golf launch monitor technology systems.
There is a large variety of launch monitor brands on the market ranging in cost, reliability, accuracy, and depth of data provided. Almost all makes and models will either be a camera-based launch monitor or a doppler radar-based launch monitor.
The camera or the doppler radar element is what the launch monitor is using to measure the golf ball to try and determine the launch conditions. Camera and radar launch monitors essentially use opposite methods to provide the data. Each measurement method has different strengths and weaknesses, depending on how and where they are used or which part of the game or golf swing they are measuring.
The difference between where a camera and radar-based launch monitor are positioned
For the majority of launch monitors, providing a relatively reliable ball speed and launch angle isn’t too challenging. The difficulties arise when it comes to accurately measuring the spin of the golf ball and crucially, the spin-axis (side spin) that causes curvature.
Now we will explore how the different types of launch monitors work, and their strengths and weaknesses.
Camera-based launch monitors
Camera-based launch monitors work by taking pictures of the golf ball as it moves through the monitor’s launch window. The number and quality of images taken will vary between different launch monitors.
All camera-based or optical launch monitors will take multiple images (from 2 up to 200+) of the golf ball, usually from a position opposite and slightly in front (towards the target) of the golfer at address. The images will then be compared to measure how the ball is moving immediately after impact.
Camera-based launch monitors process launch information through a ball-flight model to show the flight that the launch conditions would have caused. The quality and quantity of the images, and the launch monitor’s ability to extract the necessary measurements, will determine how accurately the launch monitor can report the launch conditions and the resultant ball flight.
An important strength of a camera-based launch monitor is that it can take direct measurements of the launch conditions, it can tell the golfer exactly how their technique is affecting the golf ball, without interference from downrange conditions. This is known as closed data.
GCQuad ball capture sequence
The Foresight Sports GCQuad uses four ultra-high-speed cameras to take up to 200 images of the golf ball within the first 30cm of ball flight. Taking the images from four different perspectives allows the GCQuad launch monitor to produce a 3D picture of the golf ball’s movement, while the high-resolution cameras allow the system to clearly see the dimple pattern of the golf ball. This is a vital component when trying to measure spin.
The onboard computer will then compare each image to the next, and using a method called spherical correlation, it will measure how the dimple pattern is rotating throughout the image set.
This process means that the GCQuad is incredibly accurate at not only measuring the ball speed and launch angles (both horizontal and vertical), but also at providing a direct measurement of the spin rate and the spin axis. The GCQuad also has the added strength of an onboard barometer and thermometer; this means it can use real-time air pressure and temperature in its ball flight model to provide the most reliable ball flight information.
Some launch monitors, as we’ve already indicated, may measure the golf club in addition to the golf ball. However, the club head speed that some launch monitors show is just a prediction based on an expected smash factor determined by the club you’ve specified to the system.
The GCQuad – regarded as the industry-leading launch monitor for club data measurement – measures club data from either 1 or 4 small reflective stickers (known as fiducials). These are stuck on the club face in specific locations to create a face outline plane that the launch monitor can track.
The GCQuad is positioned just in front of the golf ball, to the side of the golfer. From there, the cameras can look back towards the approach of the golf club, allowing it to take direct images of the face itself. From this position, the GCQuad can also measure the exact impact point of the golf ball on the club face.
The real strength of a camera-based launch monitor is that all the measurements of the launch conditions are direct measurements, not calculations. This means that they are able to produce the same reliable results whether they are used inside or outside.
Something that a camera-based launch monitor isn’t able to tell the golfer is how the golf ball was impacted by downrange conditions. For example, if there was a strong wind, the launch monitor would tell you where the golf ball would have gone in still conditions, not where it actually went in the current conditions.
Some golfers may see that as a strength or a weakness, depending on how they want to use the launch monitor. However, the simulation software does allow the user to create windy conditions to see the effect of the weather on the ball.
Radar-based launch monitors
Doppler radar launch monitors, such as Flightscope or Trackman, work the opposite way from a camera-based launch monitor. They use radar to track the flight of the golf ball and then calculate the launch conditions that would have caused that flight.
The frequency and quality of the radar, combined with the complexity and accuracy of the algorithm used to calculate the launch conditions, will determine how reliable the data produced by the launch monitor is.
Radar has been used for object tracking for over 100 years and played a major role in WW2. In its simplest form, a doppler radar system sends out a radio frequency from its transmitter, this frequency then reflects off the object in question and returns to the receiver. The time between the signal leaving the transmitter and arriving at the receiver allows the radar to calculate how far away the object is. Sending and receiving multiple signals means the radar can plot the positions of a moving object.
In the case of golf played outdoors, the radar system will transmit a signal downrange that tracks the flight of the golf ball as it sends a reflected radio wave back to the receiver. This allows the radar to plot the trajectory of the golf ball and produce a trace of the flight.
The internal computer within the launch monitor (or associated software) will then, from that tracked ball flight, try to calculate what set of launch conditions would have caused that particular ball flight and shot shape.
A strength of a radar system is being able to show where, and how far, the golf ball has travelled for each shot. This is why we see them so often for shot-tracing on television coverage. However, using this method can cause issues when it comes to calculating the launch conditions as the golf ball has already travelled a significant distance before the radar has enough data points to calculate from.
This means that downrange conditions, like wind, might have already affected or changed the flight of the golf ball. The resultant calculated launch conditions may therefore not be an accurate report of how the golfer’s technique affected the ball’s flight. This is known as ‘open data’, unlike the closed data captured by a camera launch monitor. It is down to the individual golfer to decide if they would rather know how the external conditions affected their ball flight, or how their swing and club affected it.
Much like the camera launch monitors, some doppler radar systems can also measure club data. Early doppler radar launch monitors would simply track the movement of the back of the golf club in order to report parameters such as club speed, club path and angle of attack.
The issue with measuring a single point at the back of the golf club is that for a large club head, like a wood or driver, the projection of the club face would be different to the back. This would result in significant errors in the data produced.
In the example of a Trackman 4, the market leader for radar launch monitors, the system uses two radar transmitters of different frequencies – one to measure the cub and the other to measure the ball. The radar that is focusing on the golf club sends a high-frequency signal which hits the back and edges of the club head as it approaches the golf ball. By using a high-frequency signal the radar is able to produce a ‘silhouette’ of the shape outside of the club head.
Producing this silhouette means that the radar can triangulate the centre of the club head, rather than the rear, reducing (although not eliminating) the error when measuring club data.
The real challenge for the radar system and club data is that, from behind, there is no way of seeing the club face. In order to produce club face data, radar systems use the initial tracked club head data (e.g. path / angle of attack) combined with the calculated initial launch conditions, to try and calculate how that face was positioned during the impact interval.
For example, if the radar saw a club face 4 degrees right, and a ball start direction of 2 degrees right, the radar would calculate that the face must have been 2 degrees closed to the club path.
The issue with this measurement technique is that it ignores different strike locations. So a heel or toe strike would be reflected by the radar system reporting an overly open, or overly closed club face. The same would be true for vertical launch angles and high or low impact points.
Using a radar launch monitor also raises an interesting question when it comes to indoor use. Unlike the camera launch monitors, radar cannot simply rely on the same method to measure ball data indoors, because they do not have enough data points to reliably calculate the spin and spin-axis indoors.
When switched into indoor mode, a Trackman 4 will do a relatively good job of measuring the ball speed and the horizontal / vertical launch angles, but it has to rely on additional calculations to produce a spin and a spin-axis. Any time you see an italic number, it’s showing how the system has estimated the value as it could not calculate it.
To calculate the spin-axis, a radar launch monitor will use a combination of the measured club data and the ball start direction to calculate the club face position, and from that calculation, will decipher how the golf ball would have spun. Once again, this series of calculations can be wildly distorted by off-centre strikes. This is the finding that led Jason MacNiven to switch over to a camera-based launch monitor for his club-fitting business.
Radar launch monitors have had great success when used outside and are regularly used to track data on the PGA Tour or at driving ranges. But it is important to understand how they calculate data when it comes to downrange conditions, the club face, and indoor use.
For more information about Foresight Sports’ launch monitors, please click here.
Read the next article in our Golf Launch Monitor Guide to learn about golf launch monitor applications.
You are also welcome to explore our PEAK online education platform. The training will help you understand how to read and interpret launch monitor data and let you hone in on target areas to improve your golf.
