The correct way to interpolate between two points on a sphere is using slerp.
How would one interpolate between more than two points on a sphere? So summing a set of points with different weights on the surface of a sphere?
Simply summing the points multiplied by their weights and then normalising the result is not accurate enough when the angles are large. We need ‘true’ spherical interpolation.
I asked this question on math.stackexchange.com, and someone found a paper that describes exactly this. Here it is: Spherical Averages and Applications to Spherical Splines and Interpolation