Closed curve question!

[D_D_K]

Hi,

How do I get the derivative at the last point of a closed curve as this's illustration.

Is there a better way than finding the approximate point?

Thanks in advance!

[tbrammer · Accepted solution]

In general you can use AcDbCurve::getFirstDeriv(double param, AcGeVector3d& firstDeriv) to calculate the derivative at the parameter param. This should also work for both start- and the end-parameter of a closed curve.

The bigger problem is to deal with "points of C1 discontinuity". I think the only safe way to find those points for general AcDbCurves is to retrieve the geometrically identical AcGeCurve3d with

AcDbCurve::getAcGeCurve (AcGeCurve3d*& pGeCurve, const AcGeTol& tol) 

and use

Adesk::Boolean AcDbCurve::explode(
   AcGeVoidPointerArray& explodedCurves,
   AcGeIntArray& newExplodedCurves,
   const AcGeInterval* intrvl = NULL
) const;

to split it into C1-continuous curves and determine their derivatives at start/end-parameters.

[D_D_K]

Thanks sir,

this is exactly what I needed. 🤠