You can access this dialog from the following:

• Ribbon: OpenRail Modeling > Rail > Regression.

This command displays a diagram representing curvature along the path of regression points in a horizontal alignment. The horizontal axis represents stationing along the alignment. The vertical axis indicates 1/radius.

The purpose of the curvature diagram is to help you distinguish the arcs, spirals, and tangent sections in an alignment, based on the regression data. This command operates on raw regression data; you do not need to perform any regression analysis before running this command.

The curvature at any given regression point is determined by fitting an arc through that point and the previous and next regression points (a three-point arc). The radius of the computed arc is then associated with the given regression point.

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Because the radius represented at the central horizontal axis of the graph is infinite, tangent sections are plotted along the central horizontal axis. The sign of the radius value is negative for left-hand curves and positive for right-hand curves. The radius at the first point is assumed to be the same as at the second point. The radius at the last point is the same as at second to last point.