# Synopsis

PDX_MSGT gdx_EvalPolylineDerivs(long option, T_GDX_POLYLINE *gdx_polyline, int max_deriv, double tval, double (*derivs)[3])

# Purpose

Evaluate a derivatives on a GDX polyline.

# Description

Given the valid GDX polyline definition and a parameter value, evaluates a derivatives on the polyline.

# Input

## option

### GDX_UNNORM

Unnormalize the paramter value

### GDX_FROMLEFT

Evaluate the derivatives from the left

## gdx_polyline

The GDX polyline data structure

## tval

The parameter value to evaluate

## max_deriv

The maximium derivative required

# Output

## point

The 3D evaluated point location

## derivs

The 3D deriviatives

# Return

          GDX_NOERR
          GDX_PARMOUTOFRANGE
          Low level error return
          .fi