Get centre point of multiple child objects

Hello,

How would I get the average centre of multiple objects that are parented to each other? I want the root parent (the "godfather" of all the other objects) to be able to gather all the child objects positions, add them, then multiply them by how many of them there are (this will get me the average centre if Im not mistaken).

Please help!

 

Check out this link

 

I'm sorry Diablo but I meant how to do it using Unity's functions, not the math behind it.

 

So it sounds like you've got a good plan... Get all the positions, add them up, then divide by the number of objects.

Have you tried it yet?

 

You must use the math behind it and calculate it yourself.

There is no magic function for every possible problem you can call and be done with it. It's called programming and not sorcery ^^

 

Code (csharp):

1.  
2. function calculateCentroid(centerPoints : Array){
3.   var centroid : Vector3 = new Vector3(0,0,0);
4.   var numPoints = centerPoints.length;
5.   for(var point : Vector3 in centerPoints){
6.     centroid += point;
7.   }
8.  
9.   centroid /= numPoints;
10.  
11.   return centroid;
12. }
13.  

Where centerPoints is an array of Vector3 objects representing the centers of all the objects you want to include in the calculation. This is purely the centroid. It does not account for the weighted average of their masses.

This is just the basic algorithm. You could modify its arguments to receive the "grandfather" object. Then within the function you could obtain all its children's positions before calculating the centroid.
This snippet might help: http://unity3d.com/support/documentation/ScriptReference/Transform.html

 

forum won't let me edit or delete my post, I meant to post this for my code:

Code (csharp):

1. function calculateCentroid()
2. {
3.   var centroid : Vector3 = new Vector3(0,0,0);
4.  
5.   if ( transform.childCount > 0 )
6.   {
7.      for (var child : Transform in transform)
8.     {
9.         centroid += child.transform.position;
10.     }
11.     centroid /= ( transform.childCount+1 );
12.   }
13.  
14.   transform.position = centroid;
15. }
16.  

 

Why are you adding 1 to the childCount?

 

To accommodate for the root because the child count doesn't include the root object.

Edit: So I am trying a much simpler approach to find the centre now, I have a game object labelled "middle" that is moved to the supposed centroid, it gets the proper centre for the first block I add to it but when more than two are added it just moves to far off places each time.

looks like this now:

Code (csharp):

1. function calculateCentroid()
2. {
3.   var centroid : Vector3 = Vector3.zero;
4.  
5.   if ( transform.childCount > 0 )
6.   {
7.     var allChildren = transform.gameObject.GetComponentsInChildren(Transform);
8.     for (var child : Transform in allChildren)
9.     {
10.         centroid += child.transform.position;
11.         print(child.transform.position);
12.     }
13.     centroid /= (transform.childCount+1);
14.   }
15.   GameObject.Find("middle").transform.position = centroid;
16. }
17.  

 

I believe GetComponentsInChildren already accounts for the root object itself. You don't need to add 1. Not sure if that's the problem though..

EDIT: ah wait! I think its because you're counting ALL children, not just Transforms. You should divide it by allChildren.length

 

GetComponentsInChildren does not include the Component included on the caller's GameObject.

 

Rapskalian, wouldn't "allChildren.length" return the same result as "transform.childCount"?

 

In this special case it would, because each gameobject must have a transform. This is not true for other kind of components.

Still, you must not add + 1. It's not an index, its the count. An array is zero index based, so an array of size/length/count 5 has elements with index 0, 1, 2, 3 and 4. NOT 5.

 

Thank you Tseng.

Ladies and gents, I have found the problem!

The problem was that all the objects were doing this code rather than jus the root object, it is now fixed:

Code (csharp):

1. function calculateCentroid()
2. {
3.     if ( transform.root.gameObject == transform.gameObject )
4.     {
5.         var centroid : Vector3 = Vector3.zero;
6.  
7.         if ( transform.childCount > 0 )
8.         {
9.         var allChildren = transform.gameObject.GetComponentsInChildren(Transform);
10.         for (var child : Transform in allChildren)
11.         {
12.             centroid += child.transform.position;
13.         }
14.         centroid /= (allChildren.length);
15.         }
16.         GameObject.Find("middle").transform.position = centroid;
17.     }
18. }
19.  

Thanks for the help! Now all I need to do is make the centre be affected by the mass of the objects, shouldn't be too hard.

 

Ok famous last words haha. I need help with making objects of higher mass influence the centroid more.

This is my code:

Code (csharp):

1. var centroid : Vector3 = transform.position;
2.            
3.             var allChildren = transform.gameObject.GetComponentsInChildren(Transform);
4.             for (var child : Transform in allChildren)
5.             {
6.                 centroid += child.transform.position;
7.                 centroid*= child.transform.gameObject.GetComponent(blockScr).blockMass/5;
8.             }
9.             centroid /= (allChildren.length);
10.             centroidIns.transform.position = centroid;

It works if the root object is placed at point (0,0,0), but when it is moved the centroid is moved all out of place through multiplication of the position.

 

you need to apply a weight to it (in this case mass). This link will help you : http://mathforum.org/library/drmath/view/52724.html

 

I have the weighted average working as I would want it to but only when the root object is centred at (0,0,0). Basically I want to know how I can make it so the centre of mass is in the same place (local to the root) no matter where it is.

Here is the code I am using:

Code (csharp):

1. var centroid : Vector3 = Vector3.zero;
2.             var massInfluence : Vector3 = Vector3.zero;
3.            
4.             var allChildren = transform.gameObject.GetComponentsInChildren(Transform);
5.             for (var child : Transform in allChildren)
6.             {
7.                 centroid += child.transform.position;
8.                 massInfluence = child.transform.position*child.transform.gameObject.GetComponent(blockScr).blockMass/10;
9.                 centroid += massInfluence;
10.             }
11.             centroid /= (allChildren.length);
12.            
13.             centroidIns.transform.position = centroid;
14.  

 

Here's a hint : the child transforms are local (that is, relative) to your root object. You're trying to set the root object's coordinates to a local space position that only makes sense *inside* the root object but not outside, where the root object lives. I'll leave the rest to you as an easy excercise.

 

I accept your exercise challenge, was I on the right track with my previous post?

 

Well.... I'm no math wiz, but isn't the weighted average supposed to be :

x = Sum(Nx * weight) / Sum(weight)

where Nx is each coordinate position?

 

Indeed..

Okay so here is the new code:

Code (csharp):

1. var allChildren = transform.gameObject.GetComponentsInChildren(Transform);
2.             for (var child : Transform in allChildren)
3.             {
4.                 var blockMass = child.transform.gameObject.GetComponent(blockScr).blockMass;
5.                
6.                 centroid += child.transform.position*blockMass;
7.                 massTotal += blockMass;
8.             }
9.             centroid /= (allChildren.length);
10.             centroid /= massTotal;
11.            
12.             centroidIns.transform.position = centroid;
13.  

I will contenue to try and fix this.

 

You forgot to get rid of line 9

 

UGH! Thank you Diablo! You've been a great help!

Works perfectly fine now :3

 

According to the documentation it does. http://unity3d.com/support/documentation/ScriptReference/GameObject.GetComponentsInChildren.html

Returns all components of Type type in the GameObject OR any of its children.

 

For anybody finding this, I would recommend seeing if this will work:

 

Cool necro bro