# Sweep2 "Simple sweep" option.

Hi,

I'm not sure I understand what governs the possible use of "Simple sweep" option in Sweep2.

Here's a situation where I want to do a sweep2 with the two longer curves as rails - and simple sweep is not possible.

However, if I rebuild the curves with the same amount of control points and degree - afterwards the simple sweep option is possible. Allthough, according to What, the curves has not changed in a way I can see:

Before rebuild:

Open NURBS curve
start = (6033.52,-724.687,1056.52)
end = (6054.93,-729.462,930.511)
degree = 3
control points: non-rational, count=6
knots: uniform (delta=1), domain = 0 to 3
clamped at start and end

After rebuild:

Open NURBS curve
start = (6033.52,-724.687,1056.52)
end = (6054.93,-729.462,930.511)
degree = 3
control points: non-rational, count=6
knots: uniform (delta=1), domain = 0 to 3
clamped at start and end

Best regards

- Björn

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### Replies to This Discussion

On of the rail curves does not have a uniform knot structure. When you rebuild, both curves get a uniform knot structure.  You can see this in the What command of one rails before the rebuild.

Open NURBS curve      start = (5981.12,-741.657,1023.85)      end = (5996.9,-744.789,930.511)      degree = 3      control points: non-rational, count=6       knots: non-uniform, domain = 1737.82 to 1834.26      clamped at start and end

Hi Scott,

Thanks, I did not see that at first. The left curve is different from the right one.

Pascal pointed me to a command called MakeUniform which I also tried now on this file. However, this command changed the curvature of the curve a lot where Rebuild did no such thing.

Is this intended?

What would be the difference between the two ways of making the knots uniform?

- Björn

The MakeUniform command will make the knot structure of the curve uniform, but leave the control point locations the same.  This may change the shape of the curve drastically.

The Rebuild command will create a uniform knot structure and will uniformly distribute new control points in an attempt to retain the curve shape.  While rebuild tries to keep the shape, it also can change the shape drastically.

So I figure it depends if you want to retain the control point locations (MakeUniform) or redistribute the control points (Rebuild). Depending on the curve either may or may not change the shape a lot.

Okay, thanks for clearing this out for me.

Regards

- Björn