Shifted curve rotation

Hi all,

I was just playing around with rhino by rotating a curve :

As you can see in the plane of the curve, the plane gets shifted all the time somehow (I just rotated like 2 deg. but the corresponding plane is rotated about 90 deg.). What could be the reason for this ?


its a line not a curve!It has no curvature and so you cannot explicitly compute a normal of a line. There are infinite solutions orthogonal to the tangent. I have no idea how its computed within the library, but I guess its trying to guess a good normal by its position in relation to the world plane.

Hi Tom,

yeah, its a line. Instead of using a curve component, I changed it to a line component in my component. However, the problem is still there.


The issue isn’t using curve vs line component, the issue is this

It has no curvature


A plane consists of an origin and two vectors. In the above images these vectors are y-axis and x-axis and the line is rotating around z- axis.
Why is it impossible to rotate this line without its plane jumping around ? And what does this have to that the line has no curvature?

I am not really understanding the issue with no curvature…

A frame on a curve is based on the point, tangent and the normal at a parameter. Since a line has no curvature (k=0) there is no hint for a normal. Any vector perpendicular to a tangent could be the normal vector of a line, so there are infinite solutions. If you are more strict with the definition of a normal => a normal is also known as curvature vector, you would even need to say a line has a null normal.

Make sure the gumball is set to local to the object before rotating. If your line isn’t parallel to any of the world axis you’ll get ‘unexpected’ results.


Gumball set to local object vs cplane/world.

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