Rotate a point around a second point, using a Quaternion

Could someone please help with the code required to rotate point P1 around point P2 by angle (x1,y1,z1)? Points are stored as Vector3, angle comes from transform.rotation (Quaternion). I saw transform.RotateAround but this is happening in a non-gameobject class so I don't have a "transform" as such (unless someone can tell me how I get one).

e.g. I have a Vector3 point e.g. (3,0,0) and I want to rotate this around another point e.g. (1,0,0) by 90 degrees around Y. This should give me (1,0,2) (I think!).

Thanks!

 

I think you are looking for a point on a circle given radius, position, and angle.
https://stackoverflow.com/questions...nt-on-a-circles-circumference-from-angle-in-c

 

Get a vector from P2 to P1 to get the relative change in direction
multiply that by the quat to rotate it
add P2 back to the result to bring it back to being around P2

Code (csharp):

1.  
2. Vector3 P1, P2; //your points
3. Quaternion rot; //the rotation
4.  
5. var v = P1 - P2; //the relative vector from P2 to P1.
6. v = rot * v; //rotatate
7. v = P2 + v; //bring back to world space
8.