Two r-table extrapolation methods are presented. One based on the evolution of the brightness as a function of the observation angle α and the other based on the addition of correlated variables, the relative angles. The evaluation of these methods uses a reference BRDF and the Normalized Root Mean Square Deviation as a metric. The method exhibiting less errors is applied to experimental data, r tables measured at 6 observation angles. It allows to reconstruct the sample BRDF. Integrated in a numerical lighting simulation, BRDF leads to luminance calculation from the observer's position to the horizon.