Returns the first derivative (in WCS) of a curve at the specified location
(vlax-curve-getFirstDeriv curve-obj param)
Arguments
The VLA-object to be measured.
A number specifying a parameter on the curve.
Return Values
A 3D vector list, if successful; otherwise nil.
Examples
For the following example, assume that splineObj points to the spline shown in the example of the vlax-curve-getDistAtParam function.
Obtain the start parameter of the curve:
_$ (setq startSpline (vlax-curve-getStartParam splineObj))
0.0
Obtain the end parameter of the curve:
_$ (setq endSpline (vlax-curve-getEndParam splineObj))
17.1546
Determine the first derivative at the parameter midway along the curve:
_$ (vlax-curve-getFirstDeriv splineObj
( / (- endspline startspline) 2))
(0.422631 -1.0951 0.0)
