How to read exactly the value of impedance from the plotting of Gmin vs frequency?

 Hi.

I am plotting Gmin ( optimum noise reflection coefficient) of a LNA in Smith chart.
I swept Gmin versus frequency (for example, ranging from 1GHz to 3GHz).

Is there a way to read out optimum noise impedance at my interested frequency, say 2GHz, from the curve?
I know that I can point the cursor over the curve, find the interested frequency and then read out the impedance. However, that method is not exactly at all.

How to read exactly the value of impedance from the plotting of Gmin vs frequency?