Get rotation from two points in sphere

Good morning everyone!

I've been a few days struggling with this and I've finally decided to post it here as I'm feeling totally lost...

The situation is, when I press a button, I create a new Gameobject (sphere collider which isTrigger = true) in which my hand is the center

I created a code with "OnTriggerExit" and when my hand leaves the sphere, I have that position and I instantiate an object in the map

The problem is that this object is always instantiated based on the rotation of the hand with and offset

Instantiate(NewObject, myHand.position + (offset), myHand.rotation);

But what I really want is to get the vector formed by the center of the sphere and the point where my hand left the sphere and make that object to have this rotation.

Vector3 relPosition = (sphere.position - positionWhenHandLeft.position);

I think I should use something like this relPosition in some code like this one:

Instantiate(NewObject, myHand.position + (offset), myHand.rotation);

Cases:
If I push the button the sphere appears and If I leave the sphere moving my hand to the right, I want the object to be rotated 90º in the Z axis and appear in horizontal to the right.

If in other case If I leave the sphere pointing forward diagonal I want the object to appear in the same direction that my hand did leaving the sphere

I hope some of you find this easy to solve and can help me, If you want I can show you all that I've tried which goes from "LookAt", "RotateTowards" and a lot of weird inventions.. Really thank you!

 

Based on the title alone, if you need to find a rotation between two points on a sphere (A and B), for a sphere at some center C, make two unit vectors C->A and C->B then use Quaternion.FromToRotation to determine the final quaternion of the rotation.

Code (csharp):

1. Vector3 a = /**/ ;
2. Vector3 b = /**/ ;
3. Vector3 c = /**/ ;
4.  
5. var q = Quaternion.FromToRotation((a - c).normalized, (b - c).normalized);

Additionally, you can determine the angle between these unit vectors C->A and C->B
like this

Code (csharp):

1. // angle is in radians and always in interval [0 - Pi); i.e. it always gives the smaller angle
2. static public float CalcCentralAngle(Vector3 dir1, Vector3 dir2)
3.   => Mathf.Atan2(Vector3.Cross(dir1, dir2).magnitude, Vector3.Dot(dir1, dir2));

Or alternatively, if you know the shortest distance between A and B (known as chord length),
you can do

Code (csharp):

1. static public float CalcCentralAngle(float chordLength, float radius = 1f)
2.   => 2f * Mathf.Asin(chordLength / (2f * radius));

You can also determine the (minor) arc length of that great circle if you
multiply radius with that central angle

Code (csharp):

1. var arcLength = radius * angle; // angle in radians

to convert angle to degrees

angle *= Mathf.Rad2Deg;

and back to radians

angle *= Mathf.Deg2Rad;

Right now I'm a bit slow (it's very early in the morning where I am, and I haven't had a night of sleep yet) to understand what you need exactly, so tomorrow!

 

Hi Orionsyndrome!

I have to say that your answer is beautiful. Yes, beautiful as everything that you said is not exactly what I was expecting to find but it helped me a lot to figure out how to do a lot of things that I've had in my head and yes, finally, to get with the solution that I was looking for!

Thanks again for your explanation and examples, they helped me a lot!

 

hey that's great, here are some links (to my other posts) if you want to learn more about what Quaternion.FromToRotation and Quaternion.Euler do, it might help you discover a dimension of quaternions you maybe didn't know about.