How to find the point of contact with the function OnTriggerEnter???

Question

Hi,

(sorry for my bad english!)

I'm building a little train game. I have some wagons and a locomotive all on differents positions on the track (not touching each other). When I get the locomotive to touch a wagon, my script (who is attach to the wagon) create (AddComponent) a hinge and attach the hiting object (the locomotive or another wagon) to connectedBody of the hinge. This is working fine. My problem is I need to know where the trigger enter so I can move the anchor of the hinge to the front or the back of the wagon to get realistic movements. (Am I clear???)

Here the code:

var connected : boolean = false;

function OnTriggerEnter (other : Collider) {

if (other.gameObject.tag == "Wagon") {
    if (!connected) {
        var otherBody = other.gameObject.rigidbody; 
        gameObject.AddComponent (HingeJoint);
        hingeJoint.connectedBody = otherBody;
        hingeJoint.axis.y = 1;
        hingeJoint.axis.x = 0;
        // move the anchor of the hinge to the pont of conctact (HELP!!!)
        connected = true;
    }
}

}

Thank you very much for your time and your knowledge!

Answer 1

Best Answer

Answer by PrimeDerektive · Jan 14, 2011 at 09:24 PM

OnTriggerEnter() does not handle collision information, just detects if there was a collision. So you cannot find the point of collision like you would with OnCollisionEnter().

You could however turn off isTrigger and add a rigidbody component to the object with the collider that you are running OnTriggerEnter() on, and make it a kinematic rigidbody, though. Then it would function just like a trigger, but you could use the collision information in OnCollisionEnter() and get the contact point.

Once you have that, you can get the contact point with OnCollisionEnter like this:

function OnCollisionEnter(collision : Collision){
    var contact : ContactPoint = collision.contacts[0];
        contact.point; //this is the Vector3 position of the point of contact
}

Also, your English is pretty good. :)

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efge · Jan 14, 2011 at 09:39 PM 1

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Rigidbody.is$$anonymous$$inematic ... good idea!

Jean-Luc Potvin · Jan 14, 2011 at 10:06 PM 0

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Thanks for the answer,

I did what you told me and it's working as it was with OnTriggerEnter. Now, can you explain how to get access to that contact point?

PrimeDerektive · Jan 14, 2011 at 11:46 PM 0

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Sure thing, see my updated answer.

toum · Dec 06, 2012 at 01:29 PM 2

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@efge OnCollisionEnter/Stay/Exit are not called if rigidbodies are $$anonymous$$inematics: "Note that collision events are only sent if one of the colliders also has a non-kinematic rigidbody attached." http://docs.unity3d.com/Documentation/ScriptReference/Collider.OnCollisionEnter.html

taranasus · Mar 31, 2016 at 07:05 PM 1

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Just wanted to add a small comment to this thread of a problem I've had and potentially others may do so as well. I wanted to use OnTriggerEnter ins$$anonymous$$d of OnCollisionEnter because the collision with an object will of course affect the other object in terms of physics.

HOWEVER, if you set one of the object's masses to 0, that will no longer be an issue and I find it worked really well for me :) Hope this helps out someone else reading this.

mani3307 taranasus · May 11, 2018 at 06:44 AM 0

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I think one can't set object mass to zero!

F-N taranasus · Mar 14, 2020 at 11:20 AM 0

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Thanks @tarnasus! This worked for me. Setting to kinematic didn't work for me, because collisionEnter is not called for kinematic rigidbodies. @mani3307, that's true. But you can set it to 0.0001 ;P

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Answer 2

Answer by mastermindsdei · Jan 04, 2017 at 08:49 AM

Maybe you can try using this

 other.gameObject.GetComponent<Collider>().ClosestPointOnBounds(transform.position);

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muberti · Jul 23, 2017 at 09:19 AM 0

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This works for me perfectly using onTriggerEnter(). Thank you man.

Schminitz · Oct 13, 2017 at 12:11 PM 0

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This works perfect for me! For those using OnTriggerEnter2D, ClosestPointOnBounds doesnt exists. So you can use collider2d.bounds.ClosestPoint(otherPos).

Hybris_Team · Feb 22, 2018 at 04:03 AM 0

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Where does that line of code go?

 function OnTriggerEnter (other : Collider) 
 {
 if (other.gameObject.tag == "Player")            
     {
     // Explosion Impact
     Instantiate (explosion, transform.position, transform.rotation);
     }

bigChris Hybris_Team · Oct 31, 2019 at 05:27 PM 0

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Replace "transform.position" in your Instantiate call with master$$anonymous$$dsdei's code snippet.

Hybris_Team bigChris · Nov 10, 2019 at 02:14 AM 0

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Thank you, I needed this, this week coincidentally!!! Works great!

joshuapeacock · Jun 13, 2018 at 06:19 AM 0

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This worked great for me! Thanks man!

DearUnityPleaseAddSerializableDictionaries · Sep 04, 2021 at 12:10 PM 0

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The issue is I still want to try find the closest overlapping point between two "large" colliders.

So I can't just use transform.position to approximate the other's collider. Unfortunately the solutions are to set a really small mass and not to use triggers, or approximate it using transform.position. :(

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Answer 3

Answer by luxe001 · Nov 05, 2012 at 01:13 PM

Hi, you can try that, is simple and fast for detect collision coordinate:

 function OnTriggerEnter (other : Collider) 
 { 
   print(other.transform.position);  
 }

G.B

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SimasS · Jan 27, 2015 at 09:13 PM 0

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luxe001 this was exactly what i needed! thanks mate

ls97 · May 27, 2015 at 11:19 AM 0

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I have a long boxcollider and a car but how do I check if the car is in the center of the boxcollider? I allready have a boxcollider on my car and both colliders are triggers. this is my code that gets the position:

 void OnTriggerStay(Collider col)
     {
 //        Transform linetrans;
 //        linetrans = col.transform;
 //
 //        Vector3 linepos = linetrans.position;
 //        float leftright = linepos.z - this.gameObject.transform.position.z;
 //        //Debug.Log (leftright.ToString ());
 //        Debug.Log (linepos.ToString ());
         Debug.Log (col.transform.position.ToString ());
 
 
     }

but all I get is 0,1,0 all the time, so basicly it says I'm in the same position allways. what did I do wrong?

Answer 4

Answer by aksh2143 · Jan 06, 2016 at 05:22 AM

i am stuck a bit here. i am not using any rigidbody in my object here. but still i want to find the reflect of the point where my ball collides. How can i get that outside the OnCollisionfunction? is that even possible? Both the ball and my wall has colliders bu t none of them have rigidbodiy. But still i want a reflecting vector.

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How to find the point of contact with the function OnTriggerEnter???

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