Create nodes at the center of the arc along lengthwise direction by using TCL

Dear Community Members
I want to get the centerline of a finite element mesh of curved bars.
The circumference of the bar has 5 nodes and I want to get their centers along lengthwise direction.
Due to the large number of bars, I would like to automate this task using TCL.

Please give me some good ideas.
A sample file is attached.

Thanks in advance.