With objects of this type you can compute the angular dependence of spectral values (reflectance, transmittance, 1-R-T) for a single spectral point (like a certain wavelength, for example). If you have measured data obtained by a goniometer system, you can fit them like with spectral data as discussed above.
The example below shows the reflectance vs. angle for silicon in p-polarization, featuring vanishing reflectance at the Brewster angle: