# Synopsis

PDX_MSGT gdx_ExtractSubIsoCurve(long option, MDA_PTR gdx_surf_ptr, int model, double iso_parm, double parm1, double parm2, double tolerance, int max_iters, MDA_PTR *gdx_crv_ptr)

# Purpose

Extract a portion of an iso-parametric curve from a GDX surface.

# Description

This routine extracts a portion of an iso-parametric curve from a GDX surface. The GDX iso-parametric curve is the type of curve that represents the surface in the particular iso-parametric direction. The exception is for the interior of a ruled surface and the offset surface iso-parametric curves which are approximated as GDX NURB curves. if parm1 > parm2, the portion of the desired iso curve is reversed.

# Input

## option

### GDX_UVALUE

If set, then iso_parm is a u-value (isocurve is varying in v); otherwise, iso_parm is a v-value (isocurve is varying in u).

## gdx_surf_ptr

The input surface database pointer from which a curve is to be extracted.

## model

The GDX model to create the GDX iso curve in

## iso_parm

A u- or v-value (see option). This defines which curve is to be extracted.

## parm1

Desired parameter value that the iso curve is to start.

## parm2

Desired parameter value that the iso curve is to end.

## tolerance

The tolerance used to approximate the offset surface iso-parametric curve.

## max_iters

The maximium iteration count to test for convergence for approximation

# Output

## gdx_crv_ptr

The extracted iso sub curve db_ptr.

# Tolerances

          MODEL_SPACE_PNT_TOL
          PARM_SPACE_PNT_TOL
          COPLANAR_TOL
          ZERO_TOL
          KNOT_TOL
          PNT_PROJ_TOL
          ANGLE_TOL
          .fi

# Return

          GDX_INVALIDPARMRANGE
          GDX_NOERR
          Low level error return
          .fi