Hello Vahid,

I have used matlab cftool app. to find the function of a curved surface.

https://it.mathworks.com/help/curvefit/surface-fitting.html

Regards

Thanks.

I suggest to fit a multiple (3-pl) regression equation to the 1000 points in 3D by least squares methods or by orthogonal polynomials.

Thank you Yashar T. Mehraliyev for your recommendation.

Dear Vahid Nouri,

What is the progress in the solving of the problem you have aimed at.

Go slowly, think deeply, work out perfectly.

Success is then certain.

Thank you Dhritikesh. Yes, you are right.

Dear Vahid Nouri, Thank you for recommending and acknowledging me.

I wish you continuous success in life.

No general method now. If you can upload you figure, we may give your some suggestions.

Thanks to Zhiqiang Wu . Vahid Nouri may follow the answer provided by Zhiqiang Wu . I wish Vahid Nouri success in life.