Originally Posted by Mister drool
why by image and not by sound?
The thumb of a raquet hitting a serve is pretty loud, and if you put a phone (or something similar near the service box you are aiming, it could pick up the sound of when the ball hits the gound... from both noises it could calculate the amount of time the ball traveled the air up until it hit the ground. you type in the measurements of a tennis court, from the baseline to the service box, count the height of the net, and then do the part where im bad at - the maths.
The article below on the kick serve says that the serve bounces so high because it hits the court at a large angle. Since the ball curves more it will travel a longer path. How would serve trajectory based on sound measurements affect the velocity calculation compared to a flat serve?
Rod Cross, the kick serve in "TW University" link above
For comparisons, the standard measurement has become the radar measurement after hitting the ball.