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The Golf Club | August 21, 2019

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DEV DIARY - PHYSICS IN THE GOLF CLUB

DEV DIARY – PHYSICS IN THE GOLF CLUB
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Development Diary: Adam Viljakainen – Physics and Camera Software Engineer

From the outset of this project, one of the pillars for the development team has been to have the most realistic physics possible. Below is a description of some of the things going on in our physics simulation.

 

Aerodynamic Drag

Aerodynamic drag refers to the forces acting opposite to the relative motion of any object moving through the air.

 

Magnus Force

A spinning object traveling through the air will generate lift. Put backspin on an object and the Magnus effect will produce an upward force. Topspin, a downward force. So, controlling spin means controlling, not just what happens after the ball bounces, but what happens over the entire course of flight. This is why the Magnus effect is so important in any golf simulation attempting realistic ball flight.

The Golf Club - Magnus Effect

Figure 1. Standard projectile trajectory (red), with drag (yellow), with drag & the Magnus effect (green).

 

Wind 

Our wind simulation follows the Beaufort scale, a measure that relates wind speed to observed conditions. We have modeled them all. Each level has different behaviour. If you watch the wind arrow in the HUD, the trees and the flags will behave much like the windsock and trees in this video.

Playing a round in hurricane force winds is absolutely hilarious. However, due to the name, my favourite has to be Violent Storm. Obviously these will not be available to the public. Sorry, even some of the moderately higher winds were making grown men cry in the studio.

And now… A fancy sports science video!!!

Initial ball trajectory & Spin

The initial trajectory of the ball is largely determined by the parameters of the impact between the club face and the ball. There is no “apply backspin” button in our simulation. Launch angle and back spin in our simulation is determined by attack angle, the “dynamic” or “delivered” loft of the club at impact, as well as the club head speed. The delivered loft, as opposed to the static loft stamped on the club (i.e 48 degrees on a PW), is determined by a number of factors in real life. In our game it is determined by our Attack Angle / Stance Hybrid Control. The fact is, the ball does not know you are hitting it with a 7 iron, what your wrist position is, that you swing like Charles Barkley or that you aren’t wearing any pants. It doesn’t care. If you take a 7 iron and hit a golf ball with the delivered loft and club head speed of a 9 iron, it will fly like it was hit by a 9 iron. Here is a great case study.

Here is another great video about the Myths and Misconceptions exposed by Trackman data.


These should give you all an idea of what we are trying to achieve with our Attack Angle / Stance Hybrid Control. With this control you are able to get the ball to check up, release, spin back or whatever your heart desires. What about Draws and Fades? These shots are also executed using the aforementioned control by opening and closing the club face. The more open or closed one’s stance is, the more the spin axis is tilted which results in the ball flying off to the right or the left. What we have here is a robust system that allows one to attempt any shot they can dream up. Albeit one that is still being tweaked to be perfect for distances, max club head seeds, etc.

Here’s a cool video that may be of some interest:


You might be thinking to yourself, “But Adam, we’ve already seen the twitch feeds of The Golf Club”. Look again closely. That video is real life.

 

Terrain Surfaces & Lies

Each surface in our game has unique properties describing its bounce factor, softness, roll resistance, etc. These determine how the ball interacts with the terrain. Also, each surface has variable lie depths that the ball can end up in. For example, if your drive flies directly into a fairway bunker, it will be buried. If you roll in, lucky you. Your lie isn’t as bad but you better execute your swing with high accuracy. Reductions in applied club head speed, spin, and launch angle are all determined by your lie. If the ball is above your feet, the ball will tend to veer left. Below, it will veer right. The greater this difference in height, the greater the effect. Even a small difference in height can have a significant effect on your desired target when hitting long fairway drives. You can mitigate this by adjusting your aim or opening/closing your club face to compensate. This is not in the first BETA release, but it’s on it’s way. Note, some clubs will perform better in certain lies than others. Long irons out of the deep rough will incur a higher penalty than short irons depending on how deep your ball is, the driver has a high execution penalty on fairways (if you want to risk it, swing straight). Lucky for you members, I did not implement this surface.

Lastly, a quick note on green speeds. Currently the Stimpmeter reading on our greens fall a little bit over “Slow” based on the USGA recommendations. There have been some discussions on having customizable green speeds.

 

Tree Canopy/Foliage Collision

Hitting the trees has never been more fun! Well maybe fun is the wrong word. However, if you do hit the trees the ball will behave as it would in real life. Hit a trunk and it will ricochet accurately. Fly through the canopies, depending on density of the foliage, the ball will lose velocity, maybe even slightly change direction. In short, tree foliage is not a catchers mitt!

The Golf Club - tree foliage diagram

Figure 2. The above picture shows the ball flying through different parts of the tree with different foliage densities. The green trajectory has tree foliage collision turned off completely so you can see the effect.

As you can see from the above, we take the physics of this sport very seriously. The new generation of hardware allows us to fully utilize every aspect to ensure that we offer an entertaining and accurate experience for you when you are playing The Golf Club.