Often a complex surface is very difficult to be trimmed by anything other than its own isocurve.
In the attached file I have created the curve in Rhino with the split by isocurve command.
I tried everything to try to split that surface with a curve created inside MOI (not using the curve created in Rhino), but everything failed including trying to create a new curve with the on surface snap on.
Is it possible to create such a curve inside MOI?

Hi niko, there is not currently any mechanism in MoI to extract an isocurve. It is on my list of things to add, I'm not quite sure at this point exactly when it will happen though.

- Michael

Thanks for the response Michael

How would you go about splitting that particular surface inside MOI?

Hi niko,

> How would you go about splitting that particular surface inside MOI?

It looks like in the full model you would have some kind of side wall along the end there, so probably an offset of that surface and then trim using that surface.

It would generally be more common to focus more on the side cap surface there instead, and let the trim happen by whatever got trimmed off by that cap rather than trying to trim it separate from that.

- Michael

I seem to be unable to do what you say Michael or maybe I don't understand correctly. I cut the original piece with curves. Here's the original file, hopefully that will shed some light..

Hi Niko, for your case it would be a process like this:

To start with take that large side-wall surface, and untrim it to make it a full sheet. that looks like this:



Then use Construct / Offset to generate an offset surface, like this:



Now trim your object with the offset surface, here you can see where the intersection curves are generated:



Then delete the offset surface:




Generally that would be the method to make sure you are trimming off a constant distance strip.

An isocurve is not guaranteed to be a constant distance away from an edge curve unless the surface is very regularly shaped. Isocurves come from the UV parameter space of a surface and will generally follow the shaping of the surface's control points. If control points are bunched together, the the isocurve is affected by that.

Here I'll show an exaggerated surface to demonstrate:



You can see that the isocurves extracted from this surface are not a constant distance away from the surface's edge - they narrow together where the surface narrows together and expand apart from one another where the surface's control points expand apart from one another.

But isocurve trimming can be good for things where you know the surface has been generated through profiles along a path like a sweep or a fillet surface.

For constant distance type things you may be better off using offset or Fillet which incorporates offsetting within it. That will make sure you actually get a constant distance which you otherwise won't be guaranteed with isocurves.

- Michael

Thanks.....it makes sense, now how do you untrim?

Sorry for the barrage of questions, I'm rather new to MOI and I'm evaluating its workflow for future projects..
So far I think there's a few features that still need to be implemented but its foundation and workflow are very solid and intuitive...much more than Rhino..

Hi niko - to untrim in MoI you need to select all the boundary edges (which must be unattached to other surfaces, use Edit/Separate if necessary to break a surface out from its joined neighbors to be an individual object) and then hit delete.

If you select one edge of a surface, you can also use Ctrl+A to select them all instead of manually picking them.

There's also a tutorial available here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

which covers that much more extensively. That's about how to repair a boolean that was done in the wrong place.


I think this was mentioned on the other thread as well, but just to make sure - you can use Copy/Paste to share objects back and forth between MoI and Rhino. So if you need to occasionally use a tool that is only in Rhino and not MoI that can be a pretty effective way to get things done.

- Michael

Thanks Michael..
I'm aware of the copy and paste but I just wanna see if my entire workflow can be moved to MOI.