I am currently calculating the radiation received by a surface for different orientations. The amount of light depends on 2 things:
(1) Solar Altitude (0-90)
(2) Azimuth different between the window and the sun (0-180)
By numerical method, I have found the radiation level for different (1) and (2) (91*181= 16341 no. of data). And now, I want to find a function for the radiation level - Function(solar altitude, azimuth difference)=VDF. Does anyone know how to find the function? I found a lot of books which only describes how to find the relation with only 1 variable ( y=f(x)). How to find the function y=f(x1,x2)?


Different lines represent radiation at different solar altitude.