Hi Mark, also see this previous post for some more illustrations:

http://moi3d.com/forum/index.php?webtag=MOI&msg=1359.6

- Michael

Thanks, Michael, that's just what I needed.
Mark

Oops! I spoke too soon.
What I really wanted was a surface that curved down into the "valley", so to speak, not up over the "mountain", which is what the curve that you created does.
So I went back and extracted a curve and drew a line across the widest part (it turns out that this line didn't do me any good)...step 1. I extruded a curved surface "sideways"...step 2. I then extruded a curve from the same curve, but up and down...step 3. Then I used the boolean merge command to get a surface. I deleted off all the unwanted parts...step 4. Finally, I tried to move the surface to the top of the tube to cap off the internal hole. Unforunately, the surface and the hole don't quite line up...step 5. I suspect that all this is caused by the fact that the curve is not perfectly symmetrical from side to side.

I wish there was a command that would just "stretch" a surface across the curve from side to side without having to go through all the intermediate steps.

Is it possible to do what I'm trying to do?

Frustrated,
Mark

Hi Mark -

> What I really wanted was a surface that curved down into the
> "valley", so to speak, not up over the "mountain", which is what
> the curve that you created does.

So that means that you want to do the same construction that I showed above, but with a 2D profile from the other direction.

Note that if you look at your curve, it has a 2D profile in both the Back and the Left side viewports like this:



So it is possible to pick between 2 different 2D profiles to build the extrusion - I happened to pick the one that seemed to match the direction that you used to cut off the top of the solid.

If you want to do the other direction, you will need to create a 2D curve flat in the other view and then extrude that one instead.


> Is it possible to do what I'm trying to do?

Yes - but there is no special command for it, just like a lot of things you may need to piece together what you need by using several existing tools. If there was a special tool for every single kind of different surfacing situation, that would mean there would be 100 different tools in a huge menu that would be nearly impossible to navigate.

To get what you need in this case you need to slice the 3D curve into exactly half and then flatten it down to 2D to get the 2D profile curve to extrude.

- Michael

Hi Mark, I've attached here the result of building the extrusion in the other direction, is this what you needed?

There are a few kind of tricky steps for extracting the 2D profile curve, because when you flatten half of a 3D curve you can get stacked up control points at the end regions, so you need to do a few different steps like using the Rebuild command on the curve to simplify its control point structure and make sure that it is exactly symmetrical, and then remove a couple of stacked up control points from the ends after squishing it flat.

Maybe in the future there could be some command to help with this, and in fact I do want to make a command that can fit a surface through a generic 3D curve - but it will be a pretty tricky thing to make that command recognize that 3D curve could be fit with an extruded surface from either direction instead of just squishing a more arbitrary surface to it.

- Michael