NAME

       c_ftkurv - interpolation for parametric curves

FUNCTION PROTOTYPE

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

SYNOPSIS

       int c_ftkurv (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.

       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_ftkurv returns an error value as per:

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

USAGE

       This function calculates an interpolatory spline under tension through a sequence of points in the plane.

       Given  a  sequence  of  input  points  (  (x[0],y[0]),  ...  , (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[0],y[0])  and  the  value  1.  is  mapped  onto
       (x[n-1],y[n-1]).

       c_ftkurv  is  called  after  all  of  the  desired  values for control parameters have been set using the
       procedures c_ftseti, c_ftsetr, c_ftsetc. Control parameters that apply to c_ftkurv are:  sig,  sl1,  sln,
       sf1.

       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).

       The  value  for  parameter sl1 is in radians and contains the slope at (x[0],y[0]). The angle is measured
       counter-clockwise from the X axis and the positive sense of the curve is assumed to be that  moving  from
       point 0 to point n-1. A value for sl1 may be omitted as indicated by the switch sf1.

       The  value  for  parameter  sln  is  in  radians  and contains the slope at (x[n-1],y[n-1]). The angle is
       measured counter-clockwise from the X axis and the positive sense of the curve  is  assumed  to  be  that
       moving from point 0 to point n-1. A value for sln may be omitted as indicated by the switch sf1.

       The  value of sf1 controls whether to use the values for sl1 and sln, or compute those values internally.
       Specifically, sf1

       = 0 if sl1 and sln are user-specified.
       = 1 if sl1 is user-specified, but sln is internally calculated.
       = 2 if sln is user-specified, but sl1 is internally calculated.
       = 3 if sl1 and sln are internally calculated.

ACCESS

       To use c_ftkurv, 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

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.

UNIX                                               March 1998                                   c_ftkurv(3NCARG)