interpolation takes very long time

[scidam]

What length of the var_keys array?!
griddata should be fast, but you are trying to interpolate 8M points..!

Access to local variables via vars(), locals() is slower than direct access to them:
> python -m timeit -s "dct={'val': None}" "dct['val']=23"

Output:
0.0532 mu.sec per loop

> python -m timeit -s "val=0" "val=23"

Output:
0.023 mu.sec per loop

> python -m timeit -s "val=0" "vars()['val']=23"

Output:
0.325 mu.sec per loop

Even if we will not consider using vars()/locals() in terms of efficiency (it isn't efficient),
using it in such context is still bad practice: 1) it pollutes local environment with
new variables 2) it makes code harder to analyze (it might be not easy to imagine what variables exists)
and finally...