Hello Michael,

I like the new Inset command a lot from the first tries I had. For me it looks like a most promising way to generae quick and clean grooved-in panels in plane fuselages. Unfortunately, it seems to have quite a lot of trouble in some cases but not in others, so that it is a hit and miss matter. Usually, as indicated already, it is obvious that the geometry is way too complex for MoI to make sense of it but some other times it is very puzzling. Consider the following example:



I Boolean_Merged three simple shapes with a cylinder. The rectangle and the circle produced perfect inset panels, with an outer rim and a groove as per the distances indicated, but the oval shape, that seems to be just as smooth and regular as the other two, failed and produced something of a mess, which I found regrettable. There are definitely easy workarounds for cases like this, but still, it is a pity.

I attach the 3dm file in case you want to have a look.

Jean-Paul

Hi Jean-Paul, yeah unfortunately you will probably run into many things that will not inset, particularly with curved pieces.

The Inset command needs to do a combination of several complex calculations, including a solid offset, then a boolean merge with some coincident surfaces involved, then an additional solid offset that shrinks down the "plug".

There can be problems with any of those steps, but in particular the offset function in the geometry library that I use can only handle pretty simple cases where there is no change in topology in the generated offset.

When you have a face that is completely smooth with its surrounding area, that will require a topology change in the offset. Here I'll try to explain it -

So one part of Inset is that it tries to calculate an offset of the set of faces surrounding your selected one, where the only the selected face is actually offset and the other surrounding faces stay in place, like this:





Then each of those surfaces gets extended and intersected with each other to form connections in the offset as necessary.

But the geometry library offset is set up to expect that for each vertex and edge of the original that there will be a matching vertex and edge in the offset result. That's not always the case though, like when you have a smoothly connecting face, it will try to do something like this:





So note there that when the offset tries to get extended in that case it won't actually intersect with the neighboring face, really some additional faces need to be inserted in there, which means a change in topology which is not currently handled directly by the offsetter.

The Inset command will try to solve this when possible by trying to take the face as a completely separate surface and ignoring its connections to adjacent faces. It's easier for that additional topology to be inserted properly when there were completely unattached edges in those spots. That's the only reason why the other examples on the same surface for the circle and rectangle parts actually worked. Sometimes you may need to manually separate out a smooth surface though.

I think in your case with the ellipse part that it's probably running into the other difficult area of doing the merge with coincident surfaces though, that's also a difficult calculation as well...


Still there may be some potential improvements that I can make, possibly the merging difficulties may be easier to do something about than offset problems.


Currently it will tend to have an easier time with more blocky types of shapes.


- Michael

Hi Jean-Paul, I examined your elliptical inset problem on a cylinder, and it seems to be failing due to an incorrect offset being created by the geometry library.

So unfortunately that's not going to be something easy for me to fix anytime soon.

As part of the Inset process, it creates a "plug" object, which in your elliptical case looks like this: (3DM geometry file also attached):



Then it wants to produce an offset of that plug, keeping the top and bottom surfaces in place and only offsetting the vertical one.

That offset is getting all messed up, you can kind of see a similar problem if you open up the attached 3DM file and just offset it using the regular Construct > Offset command, it creates this:



You can see that's not a proper offset.

When the geometry library's offset mechanism creates a bad result like this, it will prevent the Inset command from working properly.


< ..... After some more examination ....>


But one of the problems in this case seems to be related to the vertical surface being a single closed surface.

It does look like there is a possible work-around for some cases like this which is to split a closed edge so that it becomes 2 edges intead of one, you can do that by selecting the edge and running Trim, with the "Add trim points" option to pick a splitting point on the side opposite of where the edge's seam is (to see the seam extrude it and watch where the seam edge is on the extruded surface). Like this:





Once that edge is split into 2 edges instead of a single closed one, then Inset seems to actually work on that face:




So that's something you can try for that case right now, and I'll take a look at doing that closed edge splitting automatically inside of the Inset command.

- Michael

Michael,
Did you know that if you run "seperate" on your plug, that it then offsets nicely?

ooops. I see that the seperation of the surfaces you are also refering to as the poor result. Not just the "Streamer".

Hi Burr, yeah when you separate things into individual surfaces, it reduces a lot of the complexity involved in the offset because it doesn't have to try to extend stuff anymore.

But without extensions there will be all kinds of gaps between the offset pieces, like if you separate a box into 6 individual surfaces and offset them you'll see that kind of result.

- Michael

Thought I was a genius! Found out I was a novice....

Michael,

Thanks for looking into this even further.

I tried as you suggested. Indeed, splitting the edges seem to help a little, but even the simple thickness seems to fail under a certain number (about 1mm in the example, and it does generate parasite surfaces on the rims that do carry over to the rest when the groove and separate height options come into play. I tried again with a fresh cylinder and oval, but it gets the same weird things happening.

With a clean smooth surface and simple shape to inset, there are easy other ways to achieve what I want, but when it comes to complex shapes like rudders or airbrakes on tailplanes and wings of aircraft, it would really help to have an automatic inset working there, but I understand that it is probably not that easy to get.

Nonetheless, in those cases when it works I am confident that the Inset command will help me a lot.

Hi Jean-Paul,


In your example, 1mm is a pretty large distance in comparison to the shape - in general a surface offset that goes a long distance away proportionally can be more difficult to calculate.

As the distance increases, any little wobbles in the surface normal become magnified, and it also can be difficult when things are approaching the same distance as the radius of the bend in the curve.

Here's kind of the classic example of how a large distance being offset around a tight bend causes bunching:



I think with 1mm in your particular example here, it is not enough distance to be fully self-intersecting like in this case above, but it still is approaching towards that and becoming more bunched.

Unfortunately calculating surface offsets has several complicated issues like this that can interfere with getting a clean result.

So you may generally just expect that trying to do a surface offset that goes a significant distance proportionally away from the original on a bendy thing is going to be problematic.




It's just not going to be realistic to expect much on complex surfaces with tight bends in them - that's not really where I expect for this to be used.

It is really meant more to be used with clean and simple shapes, but it does help to add quite a lot of interesting details really quickly to a simple shape, to turn a simple form into a more interesting one.

Here's a good example of the kind of thing that it is more oriented towards:




Things like this command tend to raise a difficult question for me - should I shy away from adding in tools that won't work with complex bendy surfaces like a rudder or an airplane wing, but that do work well with blocky objects?

If I only waited until something like this worked on all kinds of shapes and bendy surfaces, it would probably be a long time before it would ever be released.

- Michael

Hi Burr, also I was able to take a look at the case you reported earlier here:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=3295.56

where you were getting a result when going inwards, but not when going outwards.

That particular one will be fixed up in the v2 final release, there was some extra work that needs to be done for this kind of smooth connecting surface stuff that was not happening for the outwards mode but it will now.

- Michael

Your meticulous nature makes MoI very powerful. Thanks.

[quote] If I only waited until something like this worked on all kinds of shapes and bendy surfaces, it would probably be a long time before it would ever be released. [/quote]

Not at all. I fully understand that tools might sometimes fail while still being WAD (Work as Designed) if circumstances are not suitable. Still it is a help in all the other cases, and for cases when it might not work it is only for the modeller to find other ways to get to what is required. With NURBS in particular, it pays to plan ahead and think before getting into shape lofting, Boolean unioning and all that good stuff, so that finding ways to get what you want is much of the work (and even the fun).

So by all means keep new tools coming. On my part I will keep reporting cases when things might not work as I hoped. If there are bugs you will fix them in due courses and when things are just out of reach we will have to accept that too.

More generally, I am always amazed that you seem to always be able to make time available to investigate and solve issues like this, and even to answer more basic questions about how to use MoI. This makes you and MoI a very special case in the jungle of 3D software. Keep up the good work!