tag_t curve_id Input Object identifier for the curve
double * param Input Parameter at which to evaluate
int * deriv_flag Input Number of derivatives to evaluate.
UF_MODL_LOC = Return the point
UF_MODL_LOC_1STDERV = Return the
point and 1st derivative
UF_MODL_LOC_1STDERV_2NDDERV =
Return the point, 1st and 2nd derivative
double * pos_and_deriv Output Position and derivative.
Dimension of the array = 3 * (deriv_flag +1)