Question Why are all my speed calculations wrong?

I've tried a bunch of things but even when I do this:

Code (CSharp):

1.  
2.  
3.         float deltaTime = Time.deltaTime;
4.         float dist = Vector3.Distance(lastPosition, transform.position);
5.         lastPosition = transform.position;
6.  
7.         timer += deltaTime;
8.         distAccumulator += dist;
9.         if (timer >= 1)
10.         {
11.  
12.             speedText.GetComponent<Text>().text = "mph " + (distAccumulator * 2.2369362920544025f).ToString();
13.  
14.             timer = 0;
15.             distAccumulator = 0;
16.         }

it's wrong. That is a direct conversion from meters per second to MPH, I can't use it because I need to update the speed more frequently, but it is WAY off. When it reads 15 mph, it feels more like 2, and 100 mph feels more like 20. It's way off but I don't understand why, all my models and everything treat 1 Unity unit as 1 meter. It's even more off when I try dividing dist by deltaTime every frame and then multiplying by (1 / deltaTime) to get ms. This is in a FixedUpdate btw. Thank you.

 

This code is just measuring distance. It is not measuring speed. if you want speed you have to do:

Code (CSharp):

1. float distanceInMeters = disAccumulator;
2. float timeElapsed = timer;
3.  
4. float speedInMs = distanceInMeters / timeElapsed;
5. float speedInMph = speedInMs * 2.23f; // whatever this number is

Note you cannot avoid dividing by

timeElapsed

/

timer

because even though you're stopping after one second, Unity runs on discrete frames, so that if statement will run some time after 1 second has elapsed, for example 1.05 seconds or something.

 

This was just to test some stuff, 0.05 seconds doesn't explain it being several orders of magnitude off and dividing it by the exact time instead of 1 actually makes the problem slightly worse.

 

Is it actually off, or does it feel off?

Also:

You should be using Time.fixedDeltaTime instead then.

 

https://docs.unity3d.com/ScriptReference/Time-deltaTime.html

This only matters as readability issue, but not technical.

 

I actually didn’t know this, cheers.