MATLAB: Bilinear interpolation of 2D matrix

Question

I am trying to apply Bilinear/bicubic interpolation on my data set which is in text files. These text files are in a folder and name output_00.text to output_23.text. Each text file consist on three columns. First is Latitude, second is longitude and third column is temperature value at this latitude and longitude(position over earth).

Temperature column contain -9999.000 as not a number or NaN values. This NaN value appear randomly in each file. Some times it appear over start, some times in middle of data, and some times at the end in the file. It is random in appearance.

I want to interpolate these NaN values with bilinear/ bicubic interpolation technique.

This code will read each text file and interpolate it with bilinear method and save it with method_00.text.

My text files has been attached

On google i found a tool for bilinear interpolation over a image or matrix. For the time shake this code can be modify to my requirement. But How? This code as been attached with this question. Link of this tool is here http://www.mathworks.com/matlabcentral/fileexchange/43533-bilinear-interpolation-of-an-image-or-matrix

Thanks always for this kind assistance

Answer 1

Here's one approach.

Create an XY grid, but put nans in some of the Z values.

[x,y] = meshgrid(linspace(-3,3,40));
z = peaks(x,y);
m = unique(randi(numel(z),[1 50]));
z(m) = nan;
surf(x,y,z)

Now use scatteredInterpolant to fill in the missing values.

m = isnan(z(:));
F = scatteredInterpolant(x(~m),y(~m),z(~m),'linear');
z2 = z;
z2(m) = F(x(m),y(m));
surf(x,y,z2)

What's going on there is that I created a scatteredInterpolant from the locations where there weren't nans (i.e. x(~m),y(~m),z(~m)), and then I applied it at the locations where there are nans (i.e. x(m),y(m)). Does that make sense?