# Synopsis

PDX_MSGT gdx_EvalNurbSurfDerivs(long option, T_GDX_NURB_SURF *gdx_nurbs_surf, int max_u_deriv, int max_v_deriv, double uval, double vval, double derivs[][GDX_MAX_DEG+1][3])

# Purpose

Evaluate derivatives on a GDX NURB Surface.

# Description

For a given U and V parameter value, evaluates the derivatives on a GDX NURB Surface.

# Input

## option

### GDX_UNNORM

Unnormalize the parameter value

### GDX_FROMLEFT

Evaluate derivatives from the left

### GDX_FROMLOW

Find the knot span from the low direction

## gdx_nurbs_surf

The GDX NURB Surface data structure.

## max_u_deriv

The maximium U deriviative desired

## max_v_deriv

The maximium V deriviative desired

## uval

The U parameter value

## vval

The V parameter value

# Output

## derivs

The 3D mixed deriviatives

# Return

          GDX_NOERR
          GDX_PARMOUTOFRANGE
          .fi