Interpolate to fill missing values in a temperature Matrix by considering the altitude (stored in a separate matrix)

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Dear all,
I have got a matrix with temperatures (let's call it T), and a matrix with altitudes (let's call it Z). They're both 150x150.
T contains some missing values that I need to fill.
Rather than filling it with a basic linear interpolation, I need to fill it taking into account the altitude (Z).
Could you please suggest a code to fill the missing values in T weighted on Z?
Thanks a lot!
  2 Comments
dpb
dpb on 30 Apr 2023
With no more to go on than that, one would presume the location of the two already contains the variations in Z into account by position in the array. It wouldn't seem much else able to do other than interp2 around each missing location; unless, of course, the elevatioins in the other array are not representive of the location they occupy in the array -- in which case it wouldn't seem there would be sufficient data/knowledge available to do anything more, anyway, either.

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Answers (1)

Image Analyst
Image Analyst on 3 May 2023
What exactly does "missing" mean to you? You can't have "holes" in the matrix. The values must either be nan, 0, or some other value.
Did you try using interp2?
help interp2
INTERP2 2-D interpolation (table lookup). Vq = INTERP2(X,Y,V,Xq,Yq) interpolates to find Vq, the values of the underlying 2-D function V at the query points in matrices Xq and Yq. Matrices X and Y specify the points at which the data V is given. Xq can be a row vector, in which case it specifies a matrix with constant columns. Similarly, Yq can be a column vector and it specifies a matrix with constant rows. Vq = INTERP2(V,Xq,Yq) assumes X=1:N and Y=1:M where [M,N]=SIZE(V). Vq = INTERP2(V,K) returns the interpolated values on a refined grid formed by repeatedly halving the intervals K times in each dimension. This results in 2^K-1 interpolated points between sample values. Vq = INTERP2(V) is the same as INTERP2(V,1). Vq = INTERP2(...,METHOD) specifies alternate methods. The default is linear interpolation. Available methods are: 'nearest' - nearest neighbor interpolation 'linear' - bilinear interpolation 'spline' - spline interpolation 'cubic' - bicubic convolution interpolation for uniformly-spaced data. This method does not extrapolate and falls back to 'spline' interpolation for irregularly-spaced data. 'makima' - modified Akima cubic interpolation Vq = INTERP2(...,METHOD,EXTRAPVAL) specificies a method and a scalar value for Vq outside of the domain created by X and Y. Thus, Vq will equal EXTRAPVAL for any value of Yq or Xq which is not spanned by Y or X respectively. A method must be specified for EXTRAPVAL to be used, the default method is 'linear'. All the interpolation methods require that X and Y be monotonic and plaid (as if they were created using MESHGRID). If you provide two monotonic vectors, interp2 changes them to a plaid internally. X and Y can be non-uniformly spaced. For example, to generate a coarse approximation of PEAKS and interpolate over a finer mesh: [X,Y,V] = peaks(10); [Xq,Yq] = meshgrid(-3:.1:3,-3:.1:3); Vq = interp2(X,Y,V,Xq,Yq); mesh(Xq,Yq,Vq) Class support for inputs X, Y, V, Xq, Yq: float: double, single See also INTERP1, INTERP3, INTERPN, MESHGRID, griddedInterpolant, scatteredInterpolant. Documentation for interp2 doc interp2 Other uses of interp2 codistributed/interp2 gpuArray/interp2
  5 Comments
Mathieu NOE
Mathieu NOE on 7 May 2023
hello again
before you do the interpolation with interp1 , you have to make sure that the data (Zrow,Trow) are unique
use unique to remove duplicates
dpb
dpb on 7 May 2023
"...with interp1 , you have to make sure that the data (Zrow,Trow) are unique"
The functional also cannot be double-valued, so if your data follow the terrain up and down, that doesn't work, either.

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