code: func NewFromPointSet(set *geo.PointSet) *Quadtree {
  	q := New(set.Bound(), set.Length())
  
  	ps := []geo.Point(*set)
  	for i := range ps {
  		q.Insert(&ps[i])
  	}
  
  	return q
  }
docs: // NewFromPointSet creates a quadtree from a pointset.
  // Copies the points into the quad tree. Modifying the points later
  // will invalidate the quad tree and lead to unexpected result.