Rational Fraction Polynomial for Modal Parameters Extraction

Hi, I am using the code for RFP technique for modal parameters extraction. I have downloaded the code from File Exchange site and it works very well with the data I have. The final parameters you get with RFP curve fitting are natural frequencies, damping ratios and modal constants. Modal constants are printed in terms of magnitude and phase. My question is related to the modal constants. How one obtains the mode shapes if you have calculated modal constants? Are modal constants actually the residues in the partial fraction form of FRF? Does anyone have any experience with the RFP function and mode shapes calculation? Many thanks!