VolCube in RQuantLib
I have posted the same question on Quant StatckExchange (https://quant.stackexchange.com/questions/58479/volcube-in-rquantlib) before I discovered this group.
Working with RQuantLib for the first time and trying to understand how the Swaption Vol Cube is being built. I am looking at volCF2CubeK.R file and my general understanding is that we are collecting ATM lognormal volatilities first in "atmMat" which is fine. Then comes the "smirk" part I don't understand.
Why not just pass the entire set of vol spreads (with ATM being zero) for a particular tenor and expiry to QuantLib's SwaptionVolCube1 ?
It looks like there is some interpolation involved with smirk that I don't understand why it's needed.
Also, what does CF2 and K stand for in the name of this file? Why is the file not simply called VolCube.R ?
On the C++ side, I see this call and it is the "qSwSmile" parameter from R that I am struggling with.