Thank you all for the positive reply's and votes already within this short period of time
! After working so many hours on something that is only costing time you get demotivated. So i was really doubting if it was still worth it. But this really gives me a boost!
As requested I'll explain some more details of the app:
It calculates from when the racket touches the ball until the ball lands on the ground.
I have already a working app that does the whole calculation but it's definitely not a friendly app yet. So it still needs a lot of work. I am not gonna give away my secret why my calculations are accurate. But what i meant wondering of in the mathematics was more than the formula V=d/t. In fact i created a Macbook application first to calculate the whole thing. Especially the position in the field for calculating the distance seemed to be a big problem in the beginning. So i used A=USVt (singular value decomposition) to get an H-matrix to transfer coordinates from one perspective to another. As i said before i was pretty enthusiastic and i came to find all the important factors for getting the speed as accurate as possible. In the end it turned out to be relatively more simple but if you don’t walk the walk you cannot know.
Than I figured an iphone app would be better because when you go and play tennis you mostly carry your phone with ya, and it would be much more practical.
So I transfered my code into an ios app (luckily without to many complications because it’s both objective c). Unfortunately its only ios for now, sorry for the android people. But if there’s gonna be sufficient downloads I will definitely consider looking into it.
The more votes the more enthusiastic I get means the quicker I finish the app.
Thank you all so far!