The Spherical Harmonic Coefficients provided by ARKit are 2nd level harmonics in R,G and B channels.
1. Are the coefficients given with respect to the local Face Coordinate system or the global World Coordinate system?
2. What is the coordinate convention followed here for the spherical hamonic functions? Is it (1, y, z, x, xy, yz, 3z^2-1, xz, x^2-y^2) as mentioned in the paper titled "An Efficient Representation for Irradiance Environment Maps" or is it (1, x, y, z, xy, xz, yz, x^2-y^2, 3z^2-1) or some other convention I've seen in other places?
3. Given the unit normal at a given pixel(on the face) and these spherical harmonic coefficients, how do you calculate the irradiance at that point? Do the coefficients already include the constant factors associated with the normal or do you need include the constant factors in the irradiance calculation as shown in the paper titled "An Efficient Representation for Irradiance Environment Maps"?