Rotate around sphere using Quaternions with full radius

Question

Hi,

I am trying to shoot projectiles from the player's position, who is on a surface of the sphere, and make the projectiles rotate around the sphere. Here's (sloppy) 3D representation:

alt text

Same stuff but from the side view:

alt text

The projectiles rotate correctly when initializing projectiles from emit position 1 a.k.a initial position.

When I translate player's position and initialize a new projectile, it has smaller radius. The required direction should be the direction in which the green arrow is pointing at.

The code for rotation I use:

     public float projectileSpeed = 20f;     // Speed of the projectile
     public GameObject projectile;           // Projectile's template
     private GameObject aProjectile;         // Instantiated projectile
     public Vector3 centerPosition;          // origin (0,0,0)
 
     void Update() {
         if (Input.GetButtonDown("Fire1"))
         {
             Shoot(transform.position);
         }
 
         if (aProjectile != null)
         {
              var axis = Vector3.up;   // does not matter, in which direction... Let's go up, for instance...
              aProjectile.transform.RotateAround(centerPosition, axis, projectileSpeed * Time.deltaTime);
         }
     }
 
     public void Shoot(Vector3 fromPosition)
     {
         aProjectile = Instantiate(projectile, fromPosition, Quaternion.identity) as GameObject;
         thisTransform = aProjectile.transform;
     }

Camera is always facing the sphere. I've omitted player's movement script around the sphere for brevity.

Answer 1

I got it working by making such projectiles which consist of 2 parts: empty gameobject, which is used as origin, and inside there is nested sphere, which is offset.

Then, I pass a position and direction in which I'd like to shoot. LookAt makes sphere GameObject to look at its origin point. As a result, a projectile is shot in the straight direction.

         public float projectileSpeed = 20f;         // Speed of the projectile
         public GameObject projectileTemplate;       // Projectile's template
     
         private GameObject projectileClone;         // Instantiated projectile
         
         private void Update()
         {
             if (projectileClone != null)
             {
                 var axis = Vector3.right;                       // axis around which are projectiles going to rotate. Projectile's direction is 90 degrees CCW
                 var qR = Quaternion.AngleAxis(Time.deltaTime * projectileSpeed, axis);      // calculate the rotation around axis
                 projectileClone.transform.rotation *= qR;       // apply the rotation
             }
         }
     
         /// <summary>
         /// Instantiates projectiles
         /// </summary>
         /// <param name="fromPosition">Position, where projectiles start flying from</param>
         /// <param name="forward">Direction to shoot projectiles towards</param>
         public void Shoot(Vector3 fromPosition, Vector3 forward)
         {
             if (projectileClone != null)
                 Destroy(projectileClone);
     
             // We use LookAt to instantiate projetiles on the right place. Projectiles should be comprised from 2 parts: center point and GameObject
             // which rotates around its center. GameObject is on the surface of the planet.
             // We also need -1 for projectiles to appear not on the other side of the planet. 
     
             projectileTemplate.transform.LookAt(fromPosition * -1, forward);         
             projectileClone = Instantiate(projectileTemplate);
         }

Rotate around sphere using Quaternions with full radius

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