Hi Pilou,

You have to separate the surfaces before 'control point' editing.
As only single surfaces can be edited, the question would be, why the cube primitive has control point :P

That is the question :)

Hi Pilou,

> Why primitive 3D cylinder and cone have not control point ?

It's because the end caps are trimmed planes. Control points cannot be turned on for objects that have joined edges where those edges are not natural edges of the underlying surface. Otherwise if points were turned on in these situations, it would be too easy for the surfaces to pull apart and make a gap in what is supposed to be a joined edge.

See the FAQ for some more explanation and illustrations.

There's an illustration in the FAQ answer that shows the kind of gaps that would be easily caused.

You can always turn on control points for an individual surface, so you can use Edit > Separate to break the cylinder into individual surfaces and then you can show points for those.

- Michael

Hi PaQ,

> As only single surfaces can be edited, the question would be,
> why the cube primitive has control point :P

Well, it's not true that only single surfaces can be edited, that's why! ;)

What is true is that you can always see control points on single surfaces, but there are also some situations where you can see them on objects made up of joined surfaces as well.

For joined surfaces it is allowed when every edge is a natural edge of the underlying surface.

When the object is structured like that, MoI is able to show a welded point result so each adjacent surface shares a single common editable point where they touch so that when you move the point the 2 surfaces move together nicely and gaps between the trim curves will not open up like they would in other situations as shown in the FAQ illustrations.

This is the case for a box primitive, it is made up of all plane surfaces where the trim edges of the plane are on the natural boundary of the plane surface.

It will also happen in some other situations, like if you do a sweep or extrude of a segmented profile curve without producing end caps, that makes multiple surfaces but which are joined at natural edges:



- Michael

Thx for precisions !

Allright,

I've indeed used a shortcut ... didn't know that :)
Thanks for the details.