I am looking for a tool in grasshopper that converts a spline to arc segments and possibility to adjust the tolerance, similair to “convert” (to arcs) in Rhino.
There’s nothing exactly like that I think, but you can always divide your curve into segments and then construct bi-arcs using the segment end-points and end-tangents. That’s pretty much what the Rhino command does too, except it has some logic build in to adapt the division density to a tolerance.
Bullant has an implementation of convert curve to achieve this. You can also script the rhino command.