查找加速度的二阶导数-UIAccelerate

Question

Hi I'm working on an iOS app that requires finding the z value of the accelerometer and then deriving it twice of find the "Jounce" value. Heres what I have so far:

In

-(void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration

I get the "z" value of acceleration and assign it to a variable:

float currentAccc = acceleration.z;

After this I don't know how to differentiate twice. How do I differentiate in Obj-C?

Thanks

Answer 1

You'll want to know something about finite differences in order to do this.

A single discrete value is insufficient.

A first order derivative wrt time would look like this:

da/dt(t) ~ (a(t+dt)-a(t))/dt
d^2a/dt^2(t) ~ (da/dt(t+dt)-da/dt(t))/dt

(I could make this easier to read if I had LaTeX.)

You can use other formulas, but these are simplest.

The ideas are commonly understood from differential calculus.