Hi Michael,

I started working with MOI a few months ago. I must say it is a very pretty product with lots of possiblities. I am experienced in working with Alibre design and MOI turns out to be a good companion.

As an example I show you rendered images of a car I build up completely in MOI recently. But I want to improve upon creating real smooth surfaces, something I think I need your help in finding the right strategy.

I send you an example file that shows my problem. In the file you see the surfaces (red) that I connect together with blends (green) either G1 or G2. Than I try to create the surface between the blends (blue) but I cannot find the right strategy to get a smooth connection between the blends and surface. I try to do with the network option, or blend option, but in all situations one can always see that this last part (blue) is not really smoothly connected. Perhaps my demand is too high, but perhaps you can help me improve this in in this kind of situations.

Many thanks in advance!

Ron

At the moment, MOI doesn't have curvature continuity options for network surfaces, so you might struggle. Michael may be able to give you an alternate strategy.

I've seen the term "curvature continuity" used a lot on this forum.

I think I know what you mean, but can you define this? thanks

Hi Shaun,

> I've seen the term "curvature continuity" used a lot on this forum.
>
> I think I know what you mean, but can you define this? thanks

It's fairly difficult to explain very clearly, here is one previous attempt at explanation:
http://moi3d.com/forum/index.php?webtag=MOI&msg=290.2

- Michael

Hi Ron, that's basically getting to a more advanced style of surface modeling which isn't really covered well by MoI currently.

MoI does have the Blend command and the Fillet command for building smooth surfaces, but like you've seen there if you are making a sort of patchwork of surfaces you may need to smooth things out sort of between multiple directions at the same time.

For that you need a tool which MoI does not currently have, for modifying a surface to make it continuous with an adjacent neighbor. MoI does not currently have that tool. Rhino does have a tool to do that called MatchSrf, so right now for that style of building a patchwork of continuous surfaces, your best option is to get Rhino, and take those surfaces into Rhino and run MatchSrf on them, then bring them back into MoI.

I am planning on working on that tool for MoI v3 though.


For some situations, like your red piece with the green blends on it, you could probably use a different approach - instead of building them as separate pieces, make each one extended a bit so the red pieces overshoot past each other, then trim them with each other so that they all come to an initially sharp edge - join those together and then put a fillet on those edges to make the rounded edges and rounded corner area instead of trying to build all those as individual surface pieces one at a time.


- Michael

Also just another general tip on making smooth things - if you want a large area to be smooth it can be better to build it as one large surface instead of in little pieces, see these examples here:

http://moi3d.com/forum/index.php?webtag=MOI&msg=1398.18
http://moi3d.com/forum/index.php?webtag=MOI&msg=1398.19

The exception to that is if you have an area of the surface that is switching directions by going into a tight bend - areas that are tightly bent between 2 larger forms are usually better done as fillets between 2 extended surfaces rather than trying to build one surface that goes through too many shape changes in it.

- Michael

Hi Michael,

Thanks for the very quick response. As you confirm, I had the impression that specific function is missing yet. Glad to see you already have it on the wishlist for Moi V3!

I shall build on with your suggestions.

Ron

So the way you get G2 in MoI currently is to not try to do that corner patchwork and create the G2 with the command itself..

This surface is a bit different than your original, but shows what i mean..If you create the original surfaces to be blended, in the larger surface as Michael mentions, then it can be trimmed to have a "Continuous edge". Both surfaces with a continuous edge can then have the G2 blend applied.



So note that if you open this file and select one of the surface edges, the entire edge selects. I did that for these 2 edges and ran a G2.

To get that continuous edge, you can have your surface trimming object be a continuous curve, or run the Merge command on the surface edge to combine them before the blend.

It is a bit of a challenge getting curvature continuity. As you can see with the blended object in the post above, the result is not always what you would expect.

Also, in software that supports extensive surface continuity, like Solidworks, that I use, a lot of times SW will refuse to create the surface, just reporting that the continuity requested cannot be achieved. This often happens when patching a squarish hole. It is often because the bounding surfaces are not themselves surface continuous at the same degree, and the patch will fail at the corners, because of conflicting curvature. Where it does succeed, the surface can be extremely distorted and not at all what you want.

It will be quite a big job for Michael to build this in to V3.

Hi BurrMan,

Thanks for your contribution. I checked your file and I understand now how it works.

""""""""Also, in software that supports extensive surface continuity, like Solidworks, that I use, a lot of times SW will refuse to create the surface, """""""""""""

Yeah, you can see this in the file I just posted also. test_surface zip.. If you run the blend and start to move the g2 bulge value, you will see the little corner patch go first..