Calculate Projectile Distance Travelled

Unity Engine
1

Hey

I’m looking for a way to calculate how far a projectile has travelled after it has been instantiated, and until it collides and is destroyed. Atm i’m using a basic equation, distance = velocity * time, where velocity is the muzzle velocity of the projectile. The problem i’m facing is calculating the time the projectile has been alive. I’ve tried stuff like

     void Start () {
           startTime=Time.time;
     }
     void Update () {
           realTime = Time.time - startTime;
     }

As well as with different kinds of Time, they seem to work, but when standing still and shooting they all give different results (can range from a lot), e.g. standing 10m away from a target, and hitting it, the time can be quite high.

Does anyone know if there’s a proper way to determine how long the projectile was alive and how far it has actually travelled in meters?

Thanks!

2

Just keep track of the position last frame. Add the distance between that and the current position to a running count, and you have your distance traveled.

private Vector3 lastPosition;
private float distanceTraveled;

private void Update()
{
    distanceTraveled += Vector3.Distance(transform.position, lastPosition);
    lastPosition = transform.position;
}
1 Like
3

Unfortunately that doesn’t work either, when hitting a target 1m away, or even 1000m away, it just shows values between 1400 to 1500

4

It should be in FixedUpdate instead of Update, since you’re presumably using physics, but aside from that it would work fine. (Well, also there should be a Start function that does “lastPosition = transform.position”.)

–Eric

2 Likes
5

Unfortunately that doesn’t seem to be working either, although it’s somewhat more accurate, it gives results in multiples of 8, so it only reports 0, 8, 16, 32, etc…

6

Don’t know what you are doing with the distance, but hopefully this should help.

using UnityEngine;
using System.Collections;

public class Foo : MonoBehaviour {

    // Instantiated position
    private Vector3 instPos;
    private float instTime;

    // Called when instantiated by default
    // Also will be called when script is enabled, helps when pooling
    private void OnEnable ()
    {
        instPos = transform.position;
        instTime = Time.time;
    }
    // Called when destroyed by default
    private void OnDisable ()
    {
        float dist = Vector3.Distance (instPos, transform.position);
        float timeDiff = Time.time - instTime;
    }
}
7

It definitely works. You’re doing something different in your code.

–Eric

1 Like
8

I can confirm that! It works perfectly fine for me as well. Many thanks @Dameon_