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In the parametric modecertain constraints are automatically applied to straight and arc centerlines.
Straight Centerline
Constraints such as Bisector, Fixed Length, and some others can be automatically applied to the centerline. Application of the Bisector and Fixed Length constraints can be disabled in parameterization parameters setting dialog. This section describes the case when these constraints are enabled.
When building a centerline based on two segments using the By Objects method, the Bisector constraint and other constraints are applied to the centerline. Their types depend on the mutual position of the objects to which the designation is set.
•If the segments are parallel or do not intersect and the intersection point of their extensions does not lie on one of the segments, then the Three Points on Line constraint is applied to the centerline at its terminal points (Fig. a).
•If one segment intersects the extension of another segment, then in the point of their intersection the Point on Curve constraint is applied to the centerline, and in the opposite point the Three Points on Line constraint is applied (Fig. b).
•If the segments intersect, then the Point Coincidence constraint is imposed on the centerline in the point of intersection, and in the opposite point the Three Points on Line constraint is applied (Fig. c).
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Constraints applied to the centerline in case of different positions of segments
If one or both end points of the centerline are free from constraints, then the Fixed Length constraint is applied to the centerline. This occurs in the following cases:
•when building a centerline based on a segment using the By Objects or With Specifying Borders methods, if one or both borders are not specified,
•when building a centerline based on two segments using the With Specifying Borders method, if one or both borders are not specified.
Arc centerline
When building an arc centerline using the By Objects method, the Concentricity and Three Points on Line constraints are automatically applied to it (Fig. a). When building it using the With specifying borders method, in addition to the Concentricity constraint, further constraints such as Point Coincidence and Point on Curve may be applied to the arc centerline (Fig. b).
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Constraints applied to an arc centerline when using the building method:
a) By Objects, b) With Specifying Borders
During construction, the arc centerline radius is defined as the arithmetic average of radii of the arcs which were specified as reference objects. However, no constraints ensuring such a ratio in case of change of radii are applied to reference objects. If radii of reference objects change, the centerline radius stays the same. If required, these values can be linked using variables, see section General Procedure of Working with Variables.
