extract value at a specific location

Question

Meriem Deli 2016-11-25

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回答： Meriem Deli 2016-11-28

Hello,

I am trying to extract a value at a specific point based on its latitude and longitude, I have a Temperature matrix(from a netcdf file) at different latitude and longitude I should get Temperature at a specfic location that is not figuring in the matrix I tried with interp2:

Tst=interp2(T1,lon_desired,latitude-desired)

but I get NaN

Could someone help me fix this issue.

Thanks in advance

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Answer 1

dpb 2016-11-25

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Tst=interp2(T1,lon_desired,latitude-desired)

Don't supply the coordinates of the reference T array so the values requested are outside the ranges 1:N,1:M, the dimensions of the array T1 undoubtedly. See the doc for usage details; you need the first syntax shown.

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dpb 2016-11-25

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[Moved OP Answer to Comment...dpb]

I tried to put original latitude and longitude but I got an error:

>> Tstat=interp2(longitude,latitude,T1,lon,lat)
Error using griddedInterpolant
The grid vectors do not define a grid of points that match the given values.
Error in interp2>makegriddedinterp (line 226)
  F = griddedInterpolant(varargin{:});
Error in interp2 (line 136)
      F = makegriddedinterp(X, Y, V, method,extrap);

I don't know what is the problem with that syntax

dpb 2016-11-25

编辑：dpb 2016-11-26

Isn't the syntax, per se, it's the data.

From the doc,

"X and Y must be monotonic, and have the same format ("plaid") as if they were produced by meshgrid. Matrices X and Y specify the points at which the data Z is given."

Hence, X,_Y_ must have same dimensions 1:1 as does Z (your T1). If you don't have regular, full-rank MxN array(), you can't use *interp2. If that is so, then perhaps griddata will suffice.

(*) It's possible with lat/long data it's full array but may not be organized such that it's not arranged in "plaid" order.

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Answer 2

Walter Roberson 2016-11-25

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https://ww2.mathworks.cn/matlabcentral/answers/313978-extract-value-at-a-specific-location#answer_244709

You need to pass in the original latitude and longitude vectors as the first two arguments to interp2(). Currently you are just passing in the data matrix without giving any indication of what latitude or longitude the rows and columns correspond to.