MATLAB: Retaining the max value during scattered data interpolation

interpolationMATLABscattered data

Hi,

Currently scatteredinterpolant averages out the valus of duplicate data points. Is there a way or a different function to keep the max (or min) of the duplicate values when performing scattered data interpolation?

Thanks,

Aykut

Best Answer

You'll need to do this manually before calling scatteredInterpolant. There are a few ways to do it, you could use a logical mask, filter the points out, etc... but here is one method:

Use unique or uniquetol to determine where the duplicates are.
Use max to find the maximum value among each set of duplicates
Index into the array and change the value of all duplicates in each set to the maximum value.

When you call scatteredInterpolant on the resulting matrix, it will still average the duplicates, but they will all have the same value.

Related Solutions

MATLAB: Use griddata ignoring gaps in data

To interpolate without the gaps you need to remove them from the data before interpolating, request values on the full grid (including gap sites), then add the gaps back in.

If you leave the gaps in the original data, then those 0's will affect the interpolation results at neighboring sites, so they need to be discarded for the purposes of interpolation.
If you don't request values on the full grid from griddata, adding the gaps back in afterward is harder.

For example:

idx = (z ~= 0); %logical mask to keep nonzeros in z
x_adj = x(idx);
y_adj = y(idx);
z_adj = z(idx);
% interpolate on the full grid (x,y) using only the adjusted data
z_gridded = griddata(x_adj,y_adj,z_adj,x,y);
% use the mask again to restore the gaps. 
% z_gridded then includes interpolated data + gaps over the full grid (x,y)
z_gridded(~idx) = 0;

MATLAB: How to retain duplicate while using ScatteredInterpolant

1-d is sufficient to explain here.

x = [1 2 3 3 4 5];
y = [1 2 3 4 5 6];

There is a replicated x, with two distinct values of y. Exactly what do you think "retaining the duplicate" means here? What value of y should be interpolated when x==3?

A property of interpolation is that for any given x, if one of the original data points is interpolated, you should get out exactly the same value as went in. (At least, exact to within floating point trash.)

Best Answer

Related Solutions

MATLAB: Use griddata ignoring gaps in data

MATLAB: How to retain duplicate while using ScatteredInterpolant

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