1. A method for generating simulated spectral information in optical critical dimension (OCD) metrology, the method comprising: receiving, by a computing device, an intensity distribution function over a numerical aperture space for a target diffracting structure; determining, by the computing device, if there is a Wood anomaly within the numerical aperture space; and integrating over the numerical aperture space by: generating a first set of points and weights, in response to determining there is no Wood anomaly; and generating a second set of points and weights, in response to determining there is a Wood anomaly, wherein the second set of weights account for an effect of the Wood anomaly on diffraction efficiency; and rigorously computing the simulated spectral information based on the first or second set of generated points and weights.