Hi Bernard,

> This reminds me of another post where you were talking about untrimming but I can't find it...

Probably this object repair tutorial: http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17
Or also this: http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4


> Could you explain (again ?) what's "untrimming" and "retrimming".

Untrimming means removing the trim curves from a surface. Once trim curves are removed, the original surface (which is still there "underneath" all the trim curves) will be restored.

Then "retrimming" means just to trim (Edit/Trim) that large restored surface to a new set of fixed up curves.


> What is it useful for

It is useful for a couple of situations - sometimes you may want to kind of "erase" cuts that have been made on a surface because they weren't really in the desired place, as with that first tutorial above.

Another use is to clean up the messed-up results from operations that didn't do a proper job of things due to calculation bugs, like in the shell example in this thread. When you look at the corner there, the edges on the object are all a mess, pieces are sticking out where they shouldn't be, etc... To make a good quality object, messed up edges like that need to be repaired. This usually means to extract the existing trims as independent curves by Copy/Paste, then edit those curves (trim them with each other or whatever), and then erase trim curves on the surface and trim the surface with the fixed up curves.


> and how do you do that ? A bit confused as there's no "Untrim" command in MoI, right ?

It is built in to the "Delete" command - you can select trim edges and then hit Delete to remove them.

But there are a couple of restrictions - the edges to remove cannot be joined to other surfaces, select the object and do Edit/Separate if necessary.

Also to make it work you must select all the edges for an entire boundary loop. Surfaces can have one outside trimming boundary that trims away the exterior of the surface, and multiple interior boundaries that cut interior holes. Each boundary can be made up of multiple edges and to remove them you have to select all the edges for a boundary. For surfaces closed in one direction like a cylinder this also means the seam edge, it is part of the outer boundary loop.

If you just want to untrim everything on a surface, select one edge and do Ctrl+A / Select All, and then hit delete.

- Michael