# Intersect, resulting curve

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?

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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.

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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.

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