Which surface does SANDBOX use?

I’d like to know if “SANDBOX” uses “nurbs surface” or “bezier surface”.
In case if SANDBOX uses none of them, would you tell me what it is.

Sorry about my poor English but I’m a student of naval arqitecture and really know about it soon.Thank you.

There are no nurbs in SketchUp - are you writing an extension?

None. Just a plain ol’ mesh. The tools moves the vertices and that’s pretty much it.

To me it looks like just moving vertices (always UP) according to their distances from the center point (or edges or whatever is pre-selected), using the radius and a sine wave shape for lifting.
See below:

added: experiment with radius 10000 instead and calculate the z values to see if they match the values in your model.

p.s. You can (almost to accuracy) lift the center by typing the ‘Smoove’ value before you hit [Enter] and let go of the Left mouse button. Here I lifted the center of a divided edge (20 segments) to 3000mm. It came out as Z= 2999.998098mm

added text: hit [Enter] and