Question Calculating the rate of change of a variable in the Update loop

Does anyone know how it might be possible to calculate the rate of change of a variable in the update loop? Consider an example below:

Code (CSharp):

1. void Update()
2. {
3.   // Sample instantaneous values
4.   gravityX = gyro.gravity.x;  
5.   gravityY = gyro.gravity.y;
6.   gravityZ = gyro.gravity.z;
7.  
8.   // How to calculate the rate of change of these values?
9.  
10. }

In the update loop I am sampling these three instantaneous values from the device's gyroscope. But I want to see whether these values are changing, and if so, what is the rate of change. Does anyone know how this can be calculated?

 

Code (CSharp):

1.     Vector3 previousGravity;
2.  
3.     void Update()
4.     {
5.       Vector3 changeRate=(gyro.gravity-previousGravity)*Time.detaTime;
6.       previousGravity=gyro.gravity;
7.     }

 

I don't think this is quite right...

I think you mean to divide by Time.deltaTime to result in a time-stabilized "per second" value.

Essentially the two values (prev and curr) are already implicitly separated in time by the deltaTime, so we divide it out.

This also means you should guard Time.deltaTime for being greater than like 0.001f or so... in that case just return

Vector3.zero

for

changeRate

 

Oops!. I actually meant to multiply by frame rate and not frame time.

 

Could you possibly post what you think is the correct solution?

 

Just zulo's solution, with a / instead of a *.

Code (CSharp):

1. Vector3 changeRate = (gyro.gravity - previousGravity) / Time.detaTime;

 

Here you go, instantaneous gravity change (hijacking Zulo's original code):

Code (csharp):

1.     public Vector3 instantaneousGravityChange;   // value is here for you to read out
2.  
3.     Vector3 previousGravity;  // previous frame
4.  
5.     void Start()
6.     {
7.         previousGravity = gyro.gravity;   // avoid first frame false spike
8.     }
9.     void Update()
10.     {
11.  
12.       float deltaTime = Time.deltaTime;
13.  
14.       Vector3 gravity = gyro.gravity;
15.  
16.       // presume no change to handle when game paused
17.       // note: depending on your needs, you may wish to exit early
18.       // if deltaTime is too small (see check below) and leave the
19.       // instantaneousGravityChange at its last computed value.
20.       // in that case, just comment out this line:
21.       instantaneousGravityChange = Vector3.zero;
22.  
23.       // prevent divide by zero if the game should pause
24.       if (deltaTime > 0.001f)
25.       {
26.           instantaneousGravityChange = (gravity - previousGravity) / deltaTime;
27.       }
28.  
29.       // age data
30.       previousGravity = gravity;
31.     }

 

Thanks so much guys, it works! Really appreciate the help!