How to draw Clothoid Transition Curves and wholly transitional curves in AutoCAD with InnerSoft CAD





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Published on Mar 8, 2014


******Clothoid Transition Curves

The elements of a typical transitional curve formed by a circular arc and symmetrical clothoids are:

• Clothoid Transition Length (Lcth): Length of the spiral curve (red curve)
• Clothoid Deflection Angle (θ): Spiral angle or deflection angle between entry tangent and tangential direction at the end of spiral.
• Length of Circular Arc (Lc): length of the circular arc (magenta arc)
• Radius of Circular Arc (Rc): radius of the circular arc (magenta arc)
• Circular Arc Angle (α): angle of the circular arc (magenta arc)
• Tangents Deflection Angle (Ω): Total deflection angle between the two tangents (angle between magenta lines)
• Tangent Length (TI): tangent length from T (point where spiral starts) to I (tangents intersection point)
• Shift of the Curve (S): The offset of tangents to the circular curve (distance from entry tangent to blue circle)

Depending of the transition curve that you want to draw, you must input some values on the form

• Cloth-Circular-Cloth: Length of Circular Arc (Rc) and Cloth. Transition Length (Lcth)
• Cloth-Circular-Cloth: Circular Radius (Rc) and Length of Circular Arc (Lc)
• Wholly Transitional Curve: Circular Radius (Rc)

Cloth-Circular-Cloth are the usual composite curves. A wholly transitional curve consists of two clothoid curves of equal length with no central arc.

Once you execute the application, it will ask for three points that you must get on AutoCAD model space:

• Any point of the entry tangent or tangent in
• Intersection point between entry and exit tangent
• Any point of the exit tangent or tangent out

Then, the symmetrical transitional curve is drawn and all the available information is sent to the AutoCAD command line.


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