NCL Home > Documentation > Functions > Interpolation

int2p_n

Interpolates pressure levels to a different set of pressure levels on the given dimension.

Prototype

	function int2p_n (
		pin        : numeric,  
		xin        : numeric,  
		pout       : numeric,  
		linlog [1] : integer,  
		pdim   [1] : integer   
	)

	return_val  :  numeric

Arguments

pin

An array of any dimensionality containing input pressure levels. If multi-dimensional, the level dimension must be in the pdim-th position and the values must be monotonically increasing or decreasing.

xin

An array of any dimensionality containing the data to be interpolated. If pin is multi-dimensional, then these two arrays have the same dimension sizes. The level dimension must be in the pdim-th position.

pout

An array of any dimensionality containing output pressure levels with values monotonically increasing or decreasing. If multi-dimensional, the level dimension must be in the pdim-th dimension and all other dimensions must be the same as xin. If one-dimensional, then all of xin will be interpolated to the same levels. Must have the same units as pin.

linlog

A scalar integer indicating the type of interpolation:

abs(linlog) == 1 --> linear interpolation
abs(linlog) != 1 --> log interpolation

If linlog is negative, then extrapolation to levels outside the range of pin will occur. Use extrapolation with caution.

pdim

A scalar integer indicating which dimension of xin is the level dimension. Dimension numbering starts at 0.

Return value

The returned array will have the same shape as xin but the pdim-th dimension will have the size of the level dimension of pout. The return type will be double if xin is double.

Description

This function interpolates the values of the pdim-th dimension of xin from one set of pressure levels to another set of pressure levels. The interpolation can be either linear or log. Extrapolation is optional. Missing values are allowed, but they are ignored.

You can use int2p if the level dimension is the rightmost dimension.

Use the int2p_n_Wrap function if metadata retention is desired. The interface is identical.

Examples

Example 1

begin
  linlog = 2   ; ln(p) interpolation

  pi =(/ 1000.,925.,850.,700.,600.,500.,400.,300.,250., \
          200.,150.,100.,70.,50.,30.,20.,10. /)
           
  xi =(/ 28., 23., 18., 10.,  2., -4., -15.,-30.,-40., \
        -52.,-67.,-78.,-72.,-61.,-52.,-48.,-46. /)

  po =(/ 1000.,950.,900.,850.,800.,750.,700.,600.,500., \
          425.,400.,300.,250.,200.,100.,85.,70.,50.,40.,\
           30.,25.,20.,15.,10. /)

           
; Note: you could use "int2p" here as well.
  xo = int2p_n (pi,xi,po,linlog,0)
; xo will contain (/ 28.,24.71,21.37,18. ,...., -48.,-47.17,-46./).

  ; Use int2p_n_Wrap if metadata retention is desired
  ; xo = int2p_n_Wrap (pi,xi,po,linlog,0)
end

Example 2

Let p_out be four-dimensional with dimensions time, lat, lon, pout_level. Additionally, p_in and t_in are four-dimensional with dimensions time, lat, lon, pin_level. Linearly interpolate with extrapolation.

    linlog = -1
    t_out = int2p_n(p_in,t_in,p_out,linlog,3)
;   t_out is dimensioned time, lat, lon, pout_level

    ; Use int2p_n_Wrap if metadata retention is desired
    ; t_out = int2p_n_Wrap(p_in,t_in,p_out,linlog,3)

Example 3

Similar to example 2, but p_out is one-dimensional:

  t_out = int2p_n(p_in,t_in,p_out,linlog,3)
; t_out is interpolated to the uniform set of pressure levels represented by p_in

  ; Use int2p_n_Wrap if metadata retention is desired
  ; t_out = int2p_n_Wrap(p_in,t_in,p_out,linlog,3)

Example 4

Similar to example 3, but assume the input arrays are dimensioned time x level x lat x lon: