A method for determining interfacial information and critical dimensions of a sample using atomic force microscopy. Tip-specimen deconvolution is performed on the scan lines before the critical dimension information processing. Local maxima and minima or local slope change of each scan line are found on a plurality of scan lines. A best fit line is then found for the plurality of maxim and minima or slope change points. Two best fit lines may be found using a plurality of maxima or minima or slope change points. An intersection of the two best fit lines can be used to determine a critical dimension such as a transition point. Such a method may be used to determine a track width of a trapezoidal magnetic write head or may be used to determine the location of a flare point on a magnetic write head.