How exactly does the curve modifier work?

I have managed some great and interesting looking results playing with the curve modifier, but I have no control over the end result, as I have no idea how it works.

I have read whatever little there is in the wiki manual, both new and old. I have also tried using simple meshes to check out how it works, but that only increased my confusion.

So can someone explain or link to something that explains how exactly it works.

I don’t mind if the explanation is a bit mathematical as long a it’s comprehensive.

i could be wrong here, but the reason for having no control when using a curve modifier could be because the origin point of your mesh and the starting point of your curve do not line up exactly. if they do and you have say a array modifier in place the result should be perfectly controllable.

as for how the nurbs curves are computed, you might want to consult the wikipedia article.

The above is true.

To be more specific. If you add a curve, then looking down from the top view, the left point of the curve is the start point and the displacement will flow from left to right by default. The object that gets the curve modifier snaps to the center of the left point of the curve at the objects origin. So if you add both a plane and a curve to the center of a blank scene the plane would snap to the left when the modifier is added. And it would distort from left to right. If you extrude the plane up or down and add segments you would then change the deformation axis to + or - Z on the modifier and see the deformation take place from left to right. If you leave the modifier axis at the default X and you rotate the plane 90 degrees on the Y axis then you could get the plane deforming from left to right if you extruded and added segments along the X axis.

To change the direction of the deformation, edit the curve in Edit Mode by rotating moving etc the curve points. You can snap the end points to the cursor for more control of a tube going from point A to point B.

Hope this sheds some light.

Thanks Richard and JO5EF.

Can someone explain what happens here when the bezier circle is rotated along the global Y-axis? (.blend attached)

4836.blend (311 KB)

Worked fine on my pc and blender 2.57b


Rotating globally will rotate the offset of the curve compared to the curve object…does that make sense? Rotating in edit mode is slightly different in which the object will maintain orientation to an extent and changes in scale and twist. In fact, since your object is oriented in the Y axis, rotating the curve around this axis will produce the effect you’re looking at. I would then assume that if the object was oriented down the X axis the same would occur while rotating globally around the X.

Anyway the real deal in simplest terms is that you are changing the orientation of the curve compared to the object (profile) that follows it.

P.S. @ jonathandone You’re rotating the profile curve not the control curve.