Is there a way to obtain the same curve as ExtractIsocurve would get you when using the Intersect command and why does Intersect even try to interpolate a curve (tolerance setting?) ?

In a simple example here, am not seeing that when the plane surface is parallel to the isocurve direction. Perhaps you can post an example file? Also what version are you using?

In general the intersection of two NURBS surfaces cannot be represented exactly by a NURBS curve. There are exceptions to this rule. For those special cases the intersection can be represented exactly by a NURBS curve.

It is possible to represent any intersection within a specified tolerance using a NURBS curve with a sufficient number of control points.

The Intersect command finds a NURBS curve which fits the intersection within the desired tolerance. It may use more than the minimum number of control points required.

The intersection of a **straight** extrusion of a planar NURBS curve and a plane is one of the special cases to the general rule above. The intersection can be represented exactly by a NURBS curve with the same number of control points as the curve used to generate the straight extrusion. The Intersect command creates a curve which exactly matches the isocurve if the plane is aligned with the isocurve. If the plane is not aligned with an isocurve then the result of Intersect may be a more complex curve.

V6, maybe thatâ€™s why

file attached

intersect.3dm (56.8 KB)

edit:

the isocurves were not parallel to plane surface

Hi @Jure_BebiÄ‡

The CVâ€™s of your surface is not completely aligned on the top view Y-axis. Itâ€™s 0.76mm off.

If you use

`SetPT`

to â€śflattenâ€ť them, the intersection comes out clean.HTH, Jakob

PS Just to elaborate: Itâ€™s all rows of CVâ€™s, not just the last one. Iâ€™m guessing the original curve from which this was extruded is out of whack.