How to fix: Interpolation requires at least two sample points for each grid dimension.

Hi,

I am getting an error while trying to run the transectc function from the Climate Data Toolbox (https://www.chadagreene.com/CDT/transectc_documentation.html). I am using it to make an oceanographic contour plot of water temperature at different depths across a transect.

The data I am using are from CTD casts in the ocean, at 6 stations over a 165 km distance. It is set up as a matrix containing all the data obtained from the CTD casts, as follows. Essentially, this is a measurement of different properties of the water column at different depths and different stations.

allstat =

  1852×26 table

    scan     Depth     Pressure    Temperature     Cond      PSAL     Density      SV      Fluor     Turb     nBtl     lat       lon       JDay      Oxy      oxsat      PAR      logPAR    depSM     ptemp     sal00      sigT      svCM     oxysat    flag      Var26  
    _____    ______    ________    ___________    ______    ______    _______    ______    ______    _____    ____    ______    ______    ______    ______    ______    ______    ______    ______    ______    ______    ______    ______    ______    ____    _________

      338     4.957        5          3.059       3.1758    35.052    27.921     1462.8    0.9399    0.447     0      74.608    29.995    115.81    314.36     94.99     13.27    2.2781     4.948    3.0587    35.052    27.921    1462.8    7.4103     0              0
      555     5.933        6         3.0533       3.1752    35.051    27.921     1462.8    0.4098    0.645     0      74.608    29.995    115.81    314.61    95.051     13.27    1.7711     5.938     3.053    35.051    27.921    1462.8    7.4114     0      0.0029513
      568     6.932        7         3.0575       3.1756    35.051     27.92     1462.8    0.5194    0.343     0      74.608    29.995    115.81    314.48    95.022     13.27    1.3762     6.927    3.0571    35.051     27.92    1462.8    7.4106     0      0.0029513
      593     7.919        8         3.0578       3.1757    35.051    27.921     1462.8    0.4843    0.149     0      74.608    29.995    115.81    314.47    95.019     13.27    1.3119     7.917    3.0573    35.051    27.921    1462.8    7.4106     0      0.0029513
      [...]
     9078    299.62      303         1.2796        3.028    34.994    28.021     1459.9    0.0366    0.151     0        76.1    29.959    117.38    319.71    92.361    822.58    0.1075    299.62    1.2647    34.994    28.022    1459.8    7.7508     0         165.95
     9119     300.6      304         1.2797       3.0281    34.994    28.021     1459.9    0.0366    0.144     0        76.1    29.959    117.38    319.54    92.311    819.85    0.1075    300.61    1.2647    34.994    28.022    1459.9    7.7508     0         165.95
     9155    301.59      305           1.28       3.0281    34.993    28.021     1459.9    0.0366    0.157     0        76.1    29.959    117.38     319.3    92.245    809.92    0.1075    301.59     1.265    34.994    28.022    1459.9    7.7507     0         165.95
     9242     302.6      306         1.2803       3.0282    34.994    28.021     1459.9    0.0366    0.168     0        76.1    29.959    117.38    319.45    92.288    818.75    0.1075    302.58    1.2652    34.994    28.022    1459.9    7.7507     0         165.95     

The transectc(x,d,v) function creates a contour plot diagram of the variable v at the horizontal locations (or times) x and depths d. x must be a numeric array of values indicating the locations or times of each CTD profile. Inputs d and v must each be cell arrays containing depths and measurements at each CTD location.

Here, x is column 26, d is column 2 and v is column 4.

I think I have my data set up as required for the function (x as a numeric array and d&v as cell arrays), and selecting the columns of interest from the matrix containing all the CTD data:

Here are the few lines of code before I use the function – I can provide my whole code if needed (only 34 lines).

dist = table2array(allstat(:,26));
depth = table2cell(allstat(:,2));
temp = table2cell(allstat(:,4));
 
transectc(dist,depth,temp);
     

I keep running into the following error:

    Error using matlab.internal.math.interp1
    Interpolation requires at least two sample points for each grid dimension.
    
    Error in interp1 (line 188)
            VqLite = matlab.internal.math.interp1(X,V,method,method,Xqcol);
    
    Error in transectc (line 150)
          V1(:,k) = interp1(d{k},v{k},di,InterpMethod);
    
    Error in smaller_size (line 34)
    transectc(dist,depth,temp);

I have tried looking online for solutions, but I am quite new to Matlab, so I am not really sure what the error code means or how to fix it (even when reading answers on Mathworks).

[dpb]

I don't know the function and the help isn't all that instructional -- without downloading and installing it not sure can help much, but...

I'd set a breakpoint with

dbstop in transectc at 150

and look at what is being passed in at that point.

I wonder about the duplicated x values, but what are referenced in the {} at the above line that threw the error aren't so without far more than know from quick perusal about what it's actually doing, it's a stab in the dark...

[Peter Perkins]

Like dpb, I don't know anything about transectc, but the fact that it askes for cell arrays as the grid points makes me suspicious. Is it possible that it wants cell arrays of vectors? That might explain why interp1(d{k},v{k},di,InterpMethod) is throwing an error, if d{k} and v{k} are supposed to be vectors and they are scalars. Dunno.

One stylistic suggestion: you might find this more readable:

dist = allstat.Var26;
depth = mat2cell(allstat.Depth);
temp = mat2cell(allstat.Temperature);