protected final void compute() {
if (!(f.isDefined() && P.isDefined())) {
tangent.setUndefined();
return;
}
// first derivative
if (df == null || !df.isDefined()) {
tangent.setUndefined();
return;
}
// calc the tangent;
double feval[] = new double[2];
double dfeval[] = new double[2];
double tvalue = f.getClosestParameter(P, f.getMinParameter());
f.evaluateCurve(tvalue, feval);
df.evaluateCurve(tvalue, dfeval);
tangent.setCoords(-dfeval[1], dfeval[0], feval[0] * dfeval[1] - dfeval[0] * feval[1]);
if (!pointOnCurve) T.setCoords(feval[0], feval[1], 1.0);
}
