predetermined grid size for "fit" function

hi,

i am trying to fit a surface using the "fit" function:

[fitresult, gof] = fit( [data(:,1), data(:,2)], data(:,3), ft, opts );

the problem is that i am getting a very rough/pixelized surface, its size iz 51x49, the original size of the data is about 20km x 5km.

my question is it possible to use a predetermined grid in order to get a smoother surface? i know it ios possible when using the "scatteredinterpolant" function but i want to use the "fit" function.

i know that i can resize/resample my solution using "imresize", but that just duplicates the existing data. thank you for your help.