get
Because, for whatever reason, the second derivative returned by the getSecondDerivative(double t) method doesn't return the correct heading of the second derivative, this gets an approximate second derivative essentially using the limit method. I use this for its heading only.
Return
this returns the approximated second derivative.
Parameters
t
this is the t value of the parametric curve. t is clamped to be between 0 and 1 inclusive.