# ncl_c_ftkurvp - Man Page

interpolation for closed parametric curves

## Function Prototype

int c_ftkurvp (int, float [], float [], int, float [], float [], float []);

## Synopsis

`int c_ftkurvp (n, xi, yi, m, t, xo, yo);`

## Description

n

The number of input data values. (n > 1)

xi

An array containing the abscissae for the input function.

yi

An array containing the functional values (y[k] is the  functional value at x[k] for k=0,n-1).

m

The number of desired interpolated values.

t

Contains an array of values for the parameter mapping onto the  interpolated curve. Any interval [tt,tt+1.] maps onto the entire curve.

xo

An array containing the X values for the interpolated points.  t[k] maps to (xo[k],yo[k]) for k=0,m-1.

yo

An array containing the Y values for the interpolated points.  t[k] maps to (xo[k],yo[k]) for k=0,m-1.

## Return Value

c_ftkurvp returns an error value as per:

= 0 -- no error.
= 1 -- if n is less than 2.
= 2 -- if adjacent coordinate pairs coincide.

## Usage

This procedure calculates an interpolatory spline under tension through  a sequence of points in the plane forming a closed curve.

Given a sequence of distinct input points  ( (x,y), ... , (x[n-1],y[n-1]), the interpolated curve is parameterized by mapping points in the interval [0.,1.] onto the  interpolated curve. The resulting curve has a parametric representation both of whose components are  splines under tension and functions of the polygonal arc length. The value 0. is mapped onto  (x,y) and the value 1. is mapped onto (x,y) as well (completing the closed curve).

c_ftkurvp is called after all of the desired values for control parameters  have been set using the procedures c_ftseti, c_ftsetr, c_ftsetc. The only control parameter that  applies to c_ftkurvp is: sig.

The value for the parameter sig specifies the tension factor. Values  near zero result in a cubic spline; large values (e.g. 50) result in nearly a polygonal line. A typical  value is 1. (the default).

## Access

To use c_ftkurvp, load the NCAR Graphics library ngmath.

## See Also

fitgrid_params, c_ftseti, c_ftsetr, c_ftsetc.

Complete documentation for Fitgrid is available at URL
http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html

## Info

March 1998 UNIX NCAR GRAPHICS