You can access this dialog from the following:

• Ribbon: OpenRail Modeling > Regression.

This tool makes an initial best guess of all elements (line, circular arc and transition spirals). The software computes the existing versine from the regression line then determines the approximate location of transition spirals and assumes that everything outside of these zones are linear or circular arcs.

This tool works only on the plan view (regression line).

The software uses a multi-pass algorithm for creating the alignment following:

1. Create horizontal lines and circular arcs with the offset less than or equal to the tolerance.
2. Create collinear / coincident elements.
3. Attempt to replace circular arcs (that should be transition spirals) with transition spirals. In this context the software looks for three adjacent circular arcs with the middle arc's radius less than the adjacent circular arcs' radii.
4. Attempt to perform regression analysis on the entire alignment.