The rail alignment options have to do with rail recognition and alignment of the measured data to the unworn rail profile.
If One-side Alignment is enabled, a profile may be modeled and measured if the entire base, fillet and web on one side are missing. The alignment will be poorer than that of a profile where the base portions of both sides can be seen, and measurement resolution (particular in face wear and cant angle) will be degraded. A reason for enabling one-side alignment would be if one side of the rail were embedded in a roadway or flooded with high ballast.
Head-Only Models specifies that modeling may proceed even if the rail cannot be identified because the base portions are complete obscured, or it is a poor match to all selected rail types. In this case, no measurements other than track gauge and gauge face angle can be calculated. The rail head is modeled, and may be used by the RANGECAM Grinding application.
Maximum Fitting Error is the highest allowable value of the standard deviation of the error when fitting the measured profile to an unworn rail. If the fitting error exceeds this maximum, the profile will not be identified as that rail.
Minimum Points is the smallest allowable number of measured x,y points that are included when the measured rail is fit to the unworn rail profile. All points in the base, fillet, web and both faces of the measured rail are used to start with. The fitting algorithm gradually excludes points that are too far from the surface of the unworn rail. If fewer than the minimum number of points are "close enough" to the unworn rail type, it is rejected as the type of the measured profile.