@davide445,

for eg. rectangular sections made of a dense polyline, you might use `_Split`

at the corners, using the `_Point`

option on each corner, then use `_Rebuild`

with degree = 1 and point count = 2.

To rebuild a curved Polyline e.g. into a real circle, `_ExtractPt`

followed by `_Circle _FitPoints`

gives good rational circles.

To rebuild a curved polyline into a smooth curve, you might just `_Rebuild`

but with degree = 3 or more and check how accurate it gets if you change the point count. Then before doing the actual modeling, align all curve geometry eg. by projecting it into planes using commands like `_ProjectToCPlane`

or `_SetPt`

.

btw. for mesh pre-alignment i often do this ugly workaround to fit a plane surface to a mesh:

- smear a random zigzag curve an a planar area of the mesh using
`_PolylineOnMesh`

- use
`_ExtractPt`

followed by `_PlaneThroughPt`

- finally orient the resulting plane and the mesh to the grid using
`_Orient`

or `_Orient3Pt`

In general, if you start with Rhino and are doing reverse engineering work the first time, try to work with layers and colors to differentiate all jaggy polylines from smooth curves & clean lines. Only these should be used for the modeling. IÂ´d also suggest to skip other programs than core Rhino and just start with the basic commands it offers.

c.