# Synopsis

PDX_MSGT gdx_EvalPlaneDerivs(long option, T_GDX_PLANE *gdx_plane, int max_derivs, double uval, double vval, double derivs[][GDX_MAX_DEG + 1][3])

# Purpose

Evaluate a derivatives on a GDX plane

# Description

At a given U and V parameter value, evaluate derivatives on the GDX plane entity. A max_derivs of 0 is equivalent to evaluating a point on the GDX plane entity. The resulting derivatives are mixed partial derivatives in U and V. The GDX plane entity must be a valid GDX definition. A max_derivs > 1 returns zero derivative values. The first derivs index are the V derivatives with respect to U (ie derivs[1][0] is the V tangent derivative).

# Input

## option

### GDX_UNNORM

Unnormalize the parameter values

## gdx_plane

The GDX plane entity structure pointer

## max_derivs

The maximium derivative required

## uval

The surface U parameter value to evaluate

## vval

The surface V parameter value to evaluate

# Output

## derivs

The 3D mixed partial derivatives

# Return

          GDX_NOERR
          GDX_PARMOUTOFRANGE
          Low level error return
          .fi