Unwanted and inexplicable offset!

Hi,

I'm moving some of my objects like this:

transform.position += transform.right * dT * speed;

where speed is a given variable and dT is Time.deltaTime

Strangely enough (and after a good while I admit), I've noticed transform.position.z incrementing by a small fraction too!

I tried the following in the debugger:

Code (CSharp):

1. transform.right
2. {(-1.0, 0.0, 0.0)}
3.  
4. transform.position
5. {(-142.4, 0.5, 7968.2)}
6. magnitude: 7969,446
7. normalized: (0.0, 0.0, 1.0)
8. sqrMagnitude: 6,351206E+07
9. x: -142,3741
10. y: 0,5000076
11. z: 7968,174
12. Static members:
13.  
14. transform.position+=transform.right*dT*speed
15. {(-149.4, 0.5, 7968.2)}
16. magnitude: 7969,573
17. normalized: (0.0, 0.0, 1.0)
18. sqrMagnitude: 6,35141E+07
19. x: -149,3545
20. y: 0,5000076
21. z: 7968,174
22. Static members:
23.  
24. transform.position+=transform.right*dT*speed
25. {(-156.3, 0.5, 7968.2)}
26. magnitude: 7969,709
27. normalized: (0.0, 0.0, 1.0)
28. sqrMagnitude: 6,351627E+07
29. x: -156,3348
30. y: 0,5000076
31. z: 7968,176
32. Static members:
33.  
34. transform.position+=transform.right*dT*speed
35. {(-163.3, 0.5, 7968.2)}
36. magnitude: 7969,851
37. normalized: (0.0, 0.0, 1.0)
38. sqrMagnitude: 6,351853E+07
39. x: -163,3152
40. y: 0,5000076
41. z: 7968,178
42.  

See what's going on with Z? You can only see this in the debugger when you unfold the object details for higher precision.

I know floating point math is not exact, but isn't this too much deviation? The effect is pretty obvious in my game after a while.

Is this not the right way to move transforms? For the moment I'm going to change it to

transform.position=new Vector3(transform.position.x+dT*speed, transform.position.y, transform.position.z)

But can you explain what's going on here? Thoughts?

Thank you

 

What is transform.rotation? Is it precisely 0,0,0?

 

Hi!, Thanks for the quick reply

Rotation is 0, -180, 0 as per the editor. But I thought that wouldn't affect transform direction vector like transform.right in any way? Specially not in this strange way.

Here's another test I run. I didn't clean it up this time, to post quick:

Code (CSharp):

1.  
2. transform.rotation
3. {(0.0, 1.0, 0.0, 0.0)}
4. eulerAngles: (0.0, 180.0, 0.0)
5. normalized: (0.0, 1.0, 0.0, 0.0)
6. w: 0
7. x: 0
8. y: 1
9. z: 0
10. Static members:
11. transform.position
12. {(62.6, 0.5, 440.2)}
13. magnitude: 444,6725
14. normalized: (0.1, 0.0, 1.0)
15. sqrMagnitude: 197733,6
16. x: 62,59476
17. y: 0,5000001
18. z: 440,2445
19. Static members:
20. Thread finished: <Thread Pool> #3
21. transform.right
22. {(-1.0, 0.0, 0.0)}
23. magnitude: 1
24. normalized: (-1.0, 0.0, 0.0)
25. sqrMagnitude: 1,000001
26. x: -1
27. y: 0
28. z: 0
29. Static members:
30. Thread finished: <Thread Pool> #7
31. transform.right*dT*speed
32. {(-3.3, 0.0, 0.0)}
33. magnitude: 3,271693
34. normalized: (-1.0, 0.0, 0.0)
35. sqrMagnitude: 10,70397
36. x: -3,271693
37. y: 0
38. z: 0
39. Static members:
40. transform.position+=transform.right*dT*speed
41. {(59.3, 0.5, 440.2)}
42. magnitude: 444,2237
43. normalized: (0.1, 0.0, 1.0)
44. sqrMagnitude: 197334,7
45. x: 59,32307
46. y: 0,5000001
47. z: 440,2445
48. Static members:
49. transform.position+=transform.right*dT*speed
50. {(56.1, 0.5, 440.2)}
51. magnitude: 443,7988
52. normalized: (0.1, 0.0, 1.0)
53. sqrMagnitude: 196957,3
54. x: 56,05137
55. y: 0,5000001
56. z: 440,2446
57. Static members:
58. transform.position+=transform.right*dT*speed
59. {(52.8, 0.5, 440.2)}
60. magnitude: 443,3976
61. normalized: (0.1, 0.0, 1.0)
62. sqrMagnitude: 196601,4
63. x: 52,77968
64. y: 0,5000001
65. z: 440,2448
66. Static members:
67. transform.rotation
68. {(0.0, 1.0, 0.0, 0.0)}
69. eulerAngles: (0.0, 180.0, 0.0)
70. normalized: (0.0, 1.0, 0.0, 0.0)
71. w: 0
72. x: 0
73. y: 1
74. z: 0
75. Static members:
76.  

 

The transform's rotation absolutely affects transform.right (why would transform.right exist if it didn't?). If your rotation is 0,-180,0 though it shouldn't cause the Z to move. I'm wondering if there's a precision issue with that though.

As an aside, I have no idea what the code is supposed to be that you're posting. I assume some sort of custom console or something. Can you post the actual C# code that causes the issue?

 

I'm just throwing those lines at the debugger in VSCode and that's what's outputting.

The relevant code is really just what I posted at first:

transform.position += transform.right * dT * speed;

This is the whole code. And disabling the script in the editor does stop the mysterious z increment (and x, of course):

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Vehicle : MonoBehaviour {
6.  
7.     bool initialized=false;
8.  
9.     //Displacement
10.     public float speed=20f;
11.  
12.     //Stretching
13.     // float stretchingSpeed=2f;
14.     // bool stretchingRight=true;
15.     // public float stretchHighLimitX;
16.     // float stretchLowLimitX;
17.  
18.  
19.     Transform[] vehicleBodies;
20.     public float vehicleLength;
21.  
22.     //Sound
23.     public AudioSource musicOrHorns;
24.     public bool music=true;
25.     public float delayBeforePlay=0f;
26.     public float timeSinceLastPlay=0f;
27.  
28.  
29.     public void Init(float speed) {
30.         initialized = true;
31.         this.speed = speed;
32.         gameObject.SetActive(true);
33.  
34.         // stretchHighLimitX = transform.localScale.x * 1.05f;
35.         // stretchLowLimitX = transform.localScale.x * 0.95f;
36.  
37.         vehicleBodies=new Transform[transform.childCount];
38.         for (int i=0; i<transform.childCount; i++)
39.             vehicleBodies[i]=transform.GetChild(i);
40.  
41.         //Get vehicle bounds
42.         Bounds vehicleBounds = new Bounds ();
43.         MeshFilter[] meshFilters = GetComponentsInChildren<MeshFilter> ();
44.         foreach(MeshFilter meshFilter in meshFilters) {
45.             vehicleBounds.Encapsulate(meshFilter.sharedMesh.bounds);
46.         }
47.         vehicleLength = Mathf.Max (vehicleBounds.size.x, vehicleBounds.size.y, vehicleBounds.size.z);
48.  
49.         // stretchingSpeed = speed / vehicleLength / 2f;
50.  
51.         foreach (Transform body in vehicleBodies)
52.             body.localPosition = new Vector3 (vehicleLength/2f, 0f, 0f);
53.  
54.         //Sound
55.         // foreach (AudioSource aud in gameObject.GetComponentsInChildren<AudioSource>())
56.         //     if (aud.clip==null)
57.         //         musicOrHorns=aud;  
58.         musicOrHorns=gameObject.GetComponentsInChildren<AudioSource>()[1];
59.         if (musicOrHorns==null)
60.             return;
61.  
62.         music=Random.value<.025f?true:false;
63.  
64.         if (music) {
65.             musicOrHorns.clip=Resources.Load<AudioClip>("Sounds/liana");
66.             musicOrHorns.pitch=1f;
67.             musicOrHorns.loop=true;
68.             musicOrHorns.Play();
69.         }
70.         else
71.         {
72.             //If this is a truck set the correct horn, else set cars horns
73.             if (gameObject.name.StartsWith("Trailer"))
74.                 musicOrHorns.clip=Resources.Load<AudioClip>("Sounds/truckhorn");
75.             else
76.                 //Weird horns (1-3) are less likely to occur
77.                 musicOrHorns.clip=Resources.Load<AudioClip>("Sounds/horn"+(Random.value<.025f?Random.Range(1,4):Random.Range(4,16)));
78.  
79.             musicOrHorns.loop=false;
80.             musicOrHorns.pitch=Random.Range(.9f, 1.1f);
81.             delayBeforePlay=Random.Range(0f, 30f);
82.         }
83.     }
84.  
85.     // Use this for initialization
86.     protected void Start () {
87.         if (!initialized)
88.             Init (speed);
89.     }
90.  
91.     // Update is called once per frame
92.     protected void Update () {
93.         float dT = Time.deltaTime;
94.  
95.         if (GameManager.gameState==GameStates.paused)
96.             return;
97.  
98.         //Position
99.         transform.position += transform.right * dT * speed;
100.  
101.         if (transform.position.x * transform.right.x >= 250f)
102.             transform.position -= transform.right * 500f;
103.  
104.         // transform.position = new Vector3(transform.position.x+dT*speed, transform.y, transform.position.z);
105.  
106.         // if (transform.position.x * transform.right.x >= 250f)
107.         //     transform.position -= transform.right * 500f;
108.  
109.  
110.         // // Scale
111.         // if (stretchingRight) {
112.         //     transform.localScale = new Vector3 (transform.localScale.x + dT * stretchingSpeed, transform.localScale.y - dT * stretchingSpeed, transform.localScale.z);
113.  
114.         //     if (transform.localScale.x >= stretchHighLimitX) {
115.         //         stretchingRight = false;
116.         //         transform.position+=transform.right*vehicleLength*transform.localScale.x;
117.         //         foreach (Transform body in vehicleBodies)
118.         //             body.localPosition = new Vector3 (-vehicleLength/2f, body.localPosition.y, body.localPosition.z);
119.         //     }
120.         // }
121.         // else {
122.         //     transform.localScale = new Vector3 (transform.localScale.x - dT * stretchingSpeed, transform.localScale.y + dT * stretchingSpeed, transform.localScale.z );
123.  
124.         //     if (transform.localScale.x <= stretchLowLimitX) {
125.         //         stretchingRight = true;
126.         //         transform.position-=transform.right*vehicleLength*transform.localScale.x;
127.         //         foreach (Transform body in vehicleBodies)
128.         //             body.localPosition = new Vector3 (vehicleLength/2f, body.localPosition.y, body.localPosition.z);
129.         //     }
130.         // }
131.  
132.  
133.         //Sound
134.         if (musicOrHorns && !music && !musicOrHorns.isPlaying) {
135.             timeSinceLastPlay+=dT;
136.  
137.             if (timeSinceLastPlay>=delayBeforePlay) {
138.                 timeSinceLastPlay=0;
139.                 delayBeforePlay=Random.Range(musicOrHorns.clip.length*120f, musicOrHorns.clip.length*240f);
140.                 musicOrHorns.Play();
141.             }
142.         }
143.     }
144.  
145.     //My methods
146. }
147.  

As for the rotation affecting the direction vectors, I think I understand what you mean. So maybe there are rotation and position precision errors that are building up after a while, since 0f is probably not really just 0?

 

@StarManta So I'm using this for the meantime:

transform.position = new Vector3(transform.position.x+transform.right.x*dT*speed, transform.position.y, transform.position.z);

Now I see why I was using transform.right Doing the above

transform.position=new Vector3(transform.position.x+dT*speed, transform.position.y, transform.position.z)

makes some of my cars run backwards

Now I wonder if this way of moving them is as efficient as the former one, with that "new" in there? But maybe the former does exactly the same with the overloaded operators anyways? But it feels a little slower now.

 

do you have the same problem if you use


transform.position += Vector3.Left * dT * speed;

 

No, I don't. And the same is true for Vector3.right.
This makes me think I must have some very small offset in my prefabs rotation. Editor shows 0,0,0 for their rotation tho. I'm thinking perhaps this isn't exactly a problem with my script (other than I shouldn't have been doing that for my use case) nor a bug in Unity but the problem is somewhere in the modeler (Blender), export and import pipeline, especially considering up is z in Blender.
Thanks!

 

I have seen slight drifts from using a Transform's rotation even at what you would intuit would not, such as 90, 180 and 270 degree rotations.

Also when you import from Blender3D, the import step converts from Blender's right-handed coordinate system to Unity's left-handed coordinate system. That's why all Blender objects import default rotated as (-90,0,0), but if you look in the inspector, sometimes it reads as (-89.999999,0,0) for instance.