1. A method of determining one or more parameters of a sample having a textured substrate and one or more overlying films, the method comprising: acquiring data from the sample having a textured substrate and one or more overlying films by using an optical metrology device to direct light to be incident on the sample and detecting light after the incident light interacts with the sample; providing the acquired data to a computer; normalizing the acquired data with the computer using reference data from a textured reference sample; fitting the normalized data to simulated data with the computer to find simulated data with a best fit, the simulated data being associated with a model having an untextured substrate and one or more variable parameters; and reporting values of the one or more variable parameters of the model that corresponds to the simulated data with the best fit.