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# g2fsh

Interpolates a scalar quantity from a Gaussian grid to a fixed grid.

## Prototype

```	function g2fsh (
grid        : numeric,
outdims [2] : byte, short, integer or long
)

return_val  :  float or double
```

## Arguments

grid

An array of 2 or more dimensions whose rightmost two dimensions must be latitude x longitude. The values must be in ascending latitude order.

outdims

An array indicating the dimensions of the rightmost two dimensions of the output grid (outdims[0] = nlatb, outdims[1] = nlonb).

As of version 6.0.0, this can be of type byte, short, integer or long.

## Return value

The return array's dimensions are the same as grid's dimensions, except the rightmost two dimensions, nlata and nlona, are replaced by nlatb and nlonb. The type will be double if the input is double, and float otherwise.

## Description

g2fsh interpolates a scalar quantity on a Gaussian grid to a fixed grid using spherical harmonics (via the Spherepack code). Values will be in ascending latitude order.

If missing values are encountered in a 2D subsection of the input array, then no interpolation will be performed on that 2D array, and the corresponding 2D subsection of the return array will be filled with missing values.

Arrays which have dimensions [...] x nlata x nlona should not include the cyclic (wrap-around) points when invoking this function. For example, if an array x has dimensions nlata = 64 and nlona = 129, where the "129" represents the cyclic point, then the user should pass the data to g2fsh via:

```  z = g2fsh ( x(...,0:nlona-2) )  ; does not include cyclic points
```

This function can only be used on grids that span the globe. It cannot be used for limited area grids.

Please read the caveats that you should be aware of when using spherical harmonic regridding.

Use g2fsh_Wrap if retention of metadata is desired.

## Examples

Assume x is dimensioned nt x nlat x nlon. The code below interpolates from a Gaussian T63 grid (nlat=96, nlon=192) to a fixed 2.5 x 5.0 degree grid (jlat=73,ilon=72):

```  X = g2fsh (x, (/jlat,ilon/))     ; ==> X(nt,jlat,ilon)

; Use g2fsh_Wrap if metadata retention is desired
; X = g2fsh_Wrap (x, (/jlat,ilon/))     ; ==> X(nt,jlat,ilon)
```

## Errors

ier is equal to:

4 or 10 if nlona is less than 4
5 or 10 if nlata is less than 3
8 if nlonb is less than 4
9 if nlatb is less than 3