A method for facilitating an ODP measurement of a semiconductor wafer. The method includes obtaining real time wafer characteristic data for a measurement site on said wafer and detecting a measured diffraction signal from a structure within the measurement site of the wafer. The measured diffraction signal is matched with a simulated diffraction signal stored in a wafer characteristic dependent profile library. A hypothetical profile structure associated with the simulated diffraction signal in the wafer characteristic dependent profile library is then identified. The real time wafer characteristic data is used to facilitate at least one of the matching and identifying.