# ncl_c_cssgrid man page

c_cssgrid — tension spline interpolation on a sphere

## Function Prototype

```
float *c_cssgrid(int, float [], float [], float [],
int, int, float [], float [], int *);
```

## Synopsis

`float *c_cssgrid (n, rlat, rlon, f, ni, nj, plat, plon, ier)`

## Description

- n
- The number of input data points, n > 2.
- rlat
- An array containing the latitudes of the input data, expressed in degrees. The first three points must not be collinear (lie on a common great circle).
- rlon
- An array containing the longitudes of the input data, expressed in degrees.
- f
- Array containing data values. f[i] is the functional value at (rlat[i],rlon[i]) for i = 0 to n-1.
- ni
- The number of latitudes in the interpolated grid.
- nj
- The number of longitudes in the interpolated grid. ni and nj can both be 1, allowing for interpolation at a single point.
- plat
- An array containing the latitudes of the points where interpolated values are to be computed. The values in plat should be in degrees.
- plon
- An array of length nj containing the longitudes the output grid lines. The values in plon should be in degrees.
- ier
- An error return value. If *ier is returned as 0, then no errors were detected. If *ier is non-zero, then refer to the error list in cssgrid_errors for details.

## Usage

c_cssgrid is called to find an interpolating tension spline for randomly positioned data on a unit sphere.

## Return Value

c_cssgrid returns a pointer to a linear array of data that contains interpolated values at user-specified lat/lon pairs. The returned array stores its values as if they were a 2-dimensional C array with latitude being the first dimension and longitude the second dimension. That is, if out is declared as

`float *out;`

and we set:

`out = c_cssgrid(n, rlat, rlon, f, nlat, nlon, plat, plon, &ier);`

then out[i*nlon+j] is the interpolated function value at coordinate point (plat[i], plon[j]) for 0 <= i < nlat and 0 <= j < nlon. The space for out is allocated internal to c_cssgrid and is nlat * nlon floats in size.

## Access

To use c_cssgrid, load the NCAR Graphics library ngmath.

## See Also

css_overview, cssgrid_errors

Complete documentation for Cssgrid is available at URL

http://ngwww.ucar.edu/ngdoc/ng/ngmath/c…

## Copyright

Copyright (C) 2000

University Corporation for Atmospheric Research

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