Hi Mark - you're talking about this curve here?



One possible way to surface a closed curve like that is to split it into 2 halves using the Edit > Trim command (click the "Add trim points" button inside of the Trim command to set up a couple of cutting points on the curve). Once the curve is in 2 separate pieces like this:



It is then possible to use the Loft command to make a surface between them.

However, even though that is one way I don't recommend doing it that way because it makes a surface that is kind of collapsed down and pinched together where the ends are touching - it's also pretty easy for the surface to be slightly self-intersecting in those areas too.

So instead the best way to make a fill surface for that curve is actually a pretty similar process to what we were talking about before with the booleans, which is to focus on the original 2D profile curve of the shape, and use that to build a fully extended surface and then trim away the parts you don't want.

Note that when you view that closed curve from the side, it has a nice 2D profile:



So that means that you can build an extruded surface like this:





Note that the closed curve you want to surface actually resides on that extruded surface.

Now you can select the full extruded surface, and use the Edit > Trim command to cut it with that curve, to remove the outer portion that you don't want:



This kind of construction is generally much preferable to the 2-halves being lofted method because the surface has no pinching in it - if you turn on control points for the trimmed piece, note that the underlying surface is still the nice and clean extruded surface:




So somewhere you probably have the original 2D profile curve used to build that solid by cutting its ends off. That's the one that you want to extrude to get the base surface to trim.

I've attached a filled in version here as filled_curve.3dm - I was able to extract the profile curve from this face of your solid, which is where I think you copied that closed curve off of:



I used Edit > Separate on that and then turned on control points and saw that the underlying surface was an extended extrusion like this:



So working off of that surface separated from the main solid, like this:



I selected the edge that is the closed curve that you wanted to fill (I think this is the right one?):



Then I did Ctrl+C to copy the curve of that edge to the clipboard, we will want it again in a moment. Then do Ctrl+A to select all edges and then push Delete - that will do an "untrim" and remove all those trimming boundaries and recover the full original underlying surface. Now do Ctrl+V to paste in the curve we copied, and you have this:



Now you have a surface and a curve on that surface which you can use to trim it with:



But presumably you would somewhere have the original 2D curve you used to build that area of the solid to start with - if you do you don't need to do these separating and untrimming steps here, just go to that curve and extrude it to build the base surface that you then need to trim.

Hope this helps!

- Michael

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