ncl_c_ftsurf man page
c_ftsurf — 2D tension spline interpolation of rectangular data
Function Prototype
float *c_ftsurf (int, int, float *, float *, float *,
int, int, float *, float *, int *);
Synopsis
float *c_ftsurf (mi, ni, xi, yi, zi, mo, no, xo, yo, ier);
Description
 mi
The number of grid lines in the X direction. (mi > 1)
 ni
The number of grid lines in the Y direction. (ni > 1)
 xi
Pointer to an array containing m X coordinates for grid lines in the X direction.
 yi
Pointer to an array containing n Y coordinates for grid lines in the Y direction.
 zi
Pointer to m x n floats which are the functional values at the grid points defined by xi and yi.
 mo
The number of output values in the X direction.
 no
The number of output values in the Y direction.
 ier

The value *ier is an error flag as per:
= 0  no error.
= 1  if n is less than 2 or m is less than 2.
= 2  if X or Y values are not strictly increasing.
Return Value
c_ftsurf returns a pointer to an array containing mo x no floats which are the interpolated values on the grid specified by the arrays xo and yo.
Usage
This procedure calculates an interpolatory surface passing through a rectangular grid of function values. The surface computed is a tensor product of splines under tension.
c_ftsurf is called after all of the desired values for control parameters have been set using the procedures c_ftseti, c_ftsetr, c_ftsetc, c_ftsetfa. The control parameters that apply to c_ftsurf are: sig, zx1, zxm, zy1, zyn, z11, zm1, z1n, zmn, df1, df2, df3, df4, df5, df6, df7, df8
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).
zx1 is an array containing n Xpartial derivatives of the function along the line xi[0], that is zx1[j] is the Xpartial derivative at point (x[0],y[j]) for j=0,n1. This parameter may be defaulted by setting the value for df1 appropriately. The default is to compute zx1 internally. Values for zx1 can be set using the procedure c_ftsetfa.
zxm is an array containing n Xpartial derivatives of the function along the line xi[m1], that is zxm[j] is the Xpartial derivative at point (xi[m1],yi[j]) for j=0,n1. This parameter may be defaulted by setting the value for df2 appropriately. The default is to compute zx2 internally. Values for zxm can be set using the procedure c_ftsetfa.
zy1 is an array containing m Ypartial derivatives of the function along the line yi[0], that is zy1[j] is the Ypartial derivative at point (x[i],y[0]) for i=0,m1. This parameter may be defaulted by setting the value for df3 appropriately. The default is to compute zy1 internally. Values for zy1 can be set using the procedure c_ftsetfa.
zyn is an array containing m Ypartial derivatives of the function along the line yi[n1], that is zyn[j] is the Ypartial derivative at point (x[i],y[n1]) for i=0,m1. This parameter may be defaulted by setting the value for df4 appropriately. The default is to compute zyn internally. Values for zyn can be set using the procedure c_ftsetfa.
z11, zm1, z1n, zmn specify XYpartial derivatives of the function at the four corners (xi[0],yi[0]), (xi[m1],yi[0]), (xi[0],yi[n1]), (xi[m1],yi[n1]), These parameters may be defaulted by setting the values for df5, df6, df7, df8, appropriately. The default is to compute z11, zm1, z1n, zmn internally.
Access
To use c_ftsurf, 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.