Dear Vitaliy,

Thank you for your reply.

i tried your suggested solution but unfortunately it didn't work in my case...

I am attaching a part of my data here, the format is {Theta,Phi,f}

indata= {

{0.000Pi, 0.000Pi, 0.600},

{0.000Pi, 0.033Pi, 0.320},

{0.500Pi, 0.033Pi, 0.405},

{1.000Pi, 0.033Pi, 0.328},

{1.500Pi, 0.033Pi, 0.406},

{0.150Pi, 0.144Pi, 0.093},

{0.350Pi, 0.144Pi, 0.115},

{0.650Pi, 0.144Pi, 0.095},

{0.850Pi, 0.144Pi, 0.151},

{1.150Pi, 0.144Pi, 0.150},

{1.350Pi, 0.144Pi, 0.102},

{1.650Pi, 0.144Pi, 0.115},

{1.850Pi, 0.144Pi, 0.084},

{0.000Pi, 0.206Pi, 1.541},

{0.050Pi, 0.206Pi, 1.165},

{0.450Pi, 0.206Pi, -1.403},

{0.500Pi, 0.206Pi, -1.505},

{0.550Pi, 0.206Pi, -1.449},

{1.450Pi, 0.206Pi, -1.415},

{1.500Pi, 0.206Pi, -1.468},

{1.950Pi, 0.206Pi, 1.153},

{0.189Pi, 0.256Pi, -1.197},

{0.311Pi, 0.256Pi, -0.757}

}

As you can see the internal step i am using isn't necessarily regular since i am generating the data outside of mathematica.

for interpolation:

f = Interpolation;

i get the following error: "The coordinates do not lie on a structured tensor product grid"

and for:

f = Interpolation;

it just doesn't do anything..

I wonder if the data structure is the reason? If so, I'm sorry i didn't make it perfectly clear.

Is there a way to get around it?

Thank you again for your help.

Dan (Bai DaLei)