In my opinion you should use the x ray diffraction as a method that permits to obtain the lattice parameter

The procedure to calculate Miller indices for powders, using X ray diffraction, is given in the following refferences:

http://www.khwarizmi.org/system/files/activities/146/csd1.pdf

http://www.ems.psu.edu/~ryba/harbin/x-ray%20patterns%201.ppt

PL, can someone suggest how to transform weather data to generate nonlinear equations

http://www.sciencedirect.com/science/article/pii/S0020025510004342

https://arxiv.org/abs/1605.05420

These articles should help.

Thank u all