A model of a sample with a periodic or non-periodic pattern of conductive and transparent materials is produced based on the effect that the pattern has on TE polarized incident light. The model of the pattern may include a uniform film of the transparent material and an underlying uniform film of the conductive material. When the pattern has periodicity in two directions, the model may include a uniform film of the transparent material and an underlying portion that based on the physical characteristics of the periodic pattern in the TM polarization direction. When the sample includes an underlying periodic pattern that is orthogonal to the top periodic pattern, the sample may be modeled by modeling the physical characteristics of the top periodic pattern and the effect of the bottom periodic pattern. The model may be stored and used to determine a characteristic of the sample.