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Re: Interpolating a regular grid [message #47887 is a reply to message #47805]

Tue, 07 March 2006 17:34

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

David Fanning wrote:
> To interpolate your gridded array, you need to know the *indices*
> of pressure and temperature. One way to find the proper indices
> is like this:
>
> xindex = Value_Locate(p, 700.6)
> xindex = yindex + ((700.6 - p[yindex])/(p[yindex+1] - p[yindex]))
>
> yindex = Value_Locate(t, 234.56)
> yindex = yindex + ((234.56- t[yindex])/(t[yindex+1] - t[yindex]))
>
> So, now, the value you are looking for is this:
>
> interpValue = Interpolate(array, xindex, yindex)

For what it's worth, the Motley library at

http://www.dfanning.com/hadfield/idl/README.html

has a function called MGH_LOCATE which will calculated one or more
"fractional index" values in the way you have shown. It also has cousins
MGH_LOCATE2 & MGH_LOCATE2A that do the same thing for 2-D curvilinear
arrays.

Note to self: I must update that library.

--
Mark Hadfield "Kei puwaha te tai nei, Hoea tahi tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)

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		Re: Interpolating a regular grid By: David Fanning on Tue, 07 March 2006 07:10
		Re: Interpolating a regular grid By: Mark Hadfield on Tue, 07 March 2006 17:34

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