Merge paths

do the points share the same height?

of course, you only care about cases where the two circles intersect/touch each other, right? - And will you ever have your circles each have its own radius, or will you always use a shared one?

Project all points to zero-height, and apply the ray casting solution I mentioned below. Then re-apply original height to resulting points. Assuming a terrain point only has one height, the solution is still valid.

This was my result. "BaseExpanders" is a class that is attached to each game object, it uses basic sin/cos to create several points on a circle around the object. It then stores those points.

AllPoints is a collection of all of the points from all of the 'expanders'.

 public bool IsPointInCircle (Vector2 center, float radius, Vector2 position)
     {
 
         // Calculate the offset vector from the center of the circle to our position
         Vector2 offset = center - position;
 
         // Calculate the linear distance of this offset vector
         float distance = offset.magnitude;
     
         
         if (radius < distance) {
 
             // If the distance is more than our radius then the point is outside of the circle
             
             return false;
 
         }
         
         return true;
 
     }

 // we then iterate through each circle, so that we are testing each point against each circle
     foreach (BaseExpanders ex in expanders) {
         
         // create the data for this 'circle'
         Vector2 centre = new Vector2 (ex.transform.position.x, ex.transform.position.z);
         float radius = ex.BaseRadius - .1f;
     
         
         // now we have all the points (from both circles), iterate thorugh those
         foreach (Transform point in AllPoints) {
         
             // we need to check if this point belongs to this circle, if so, ignore it, as points belonging to this
             // circle should never be destroyed., only other circles.
             if (point.parent != ex.transform) {
             
                 Debug.DrawLine (point.position, ex.transform.position, Color.white);
                 
                 Vector2 v2p = new Vector2 (point.position.x, point.position.z);
                 

                 // if point is in circle, delete it.
                 if (pointUtil.IsPointInCircle (centre, radius, v2p)) {
                     // not in circle, so don't add tolist
                     point.renderer.material.color = Color.red;
                 } else {
                     BoundaryPoints.Add (point);
                     point.renderer.material.color = Color.blue;
                 }
                 
             }
                 
         }
             
             
             
     }

• Looks very nice! Glad you sorted it out.