# Synopsis

PDX_MSGT gdx_EvalParmSplSurfDerivs(long option, T_GDX_SPLINE_SURF *gdx_spline_surf, int max_u_deriv, int max_v_deriv, double uval, double vval, double derivs[][GDX_MAX_DEG + 1][3])

# Purpose

Evaluate a derivatives on a GDX parametric spline surface.

# Description

Given the GDX parametric spline surface and a U and V parameter value evaluates derivatives on the surface at the given UV parameter value.

# Input

## option

### GDX_UNNORM

Unnormalize the parameter values

### GDX_FROMLEFT

Evaluate derivatives from the left

### GDX_FROMLOW

Find the knot span from the low direction

## gdx_spline_surf

The GDX parametric spline surface data structure

## max_u_deriv

The maximium U deriviative desired

## max_v_deriv

The maximium V deriviative desired

## uval

U surface parmeter value

## vval

V surface parmeter value

# Output

## derivs

The 3D mixed derivatives

# Return

          GDX_NOERR
          GDX_PARMOUTOFRANGE
          Low level error return.
          .fi