Polygon scanning help

[Expensive_tape_measure]

Hi guys, Does anyone know the best way to scan a Polygon bore so I can check the Runout of the bore to the flange face?. I don't have any CAD drawings (for any jobs in general). I was thinking that I could scan 3 indentical Lines @120 degrees form each other,
create a Point at both ends of the line, contruct a Circle at both ends using the points and finally constructing a Cone from the Circles?. Any advice would be greatly appreciated,
Cheers

[JEFMAN]

Could you post a scheme ?
You talk about a polygon at the start, cone at the end... It's not really clear for me...

What I understand of you method doesn't allow to construct circles centered on polygon...
If you have a polygon bore like a kind of pyramid, then measure planes and construct intersection lines from them, and apply your method to pierce points of lines with faces...