Hi Michael,

these points don`t seem to belong to the structure of the object, though they are connected to it. It seems that these are polygons added to the edge of the fillet. The uv-polys i`ve shown above weren`t the original uv-polys of MOI. I`ve created them with cinema 4d/Bodypaint and only here i`ve noticed that there was something wrong. When i delete these points, the corresponding polys are deleted too and everything is fine.

Greetings Dirk

Here`s another shot from the other side.

It seems Moi or c4d uses a whole triangle for the edge of the fillet.

Hi Dirk, I suspect what you are seeing there is probably a side effect of the way that C4D decided to triangulate that n-gon.

Let me illustrate - say you have this 5 point n-gon:



Now say to produce a triangulation of this n-gon, what if the triangulator starts by placing this triangle:



Then next it places this triangle:



It certainly looks like the triangles it picked were nicely shaped, but it is actually pretty bad because now it only has one possible point left to form the last triangle, and it will be a degenerate one along the side there:



It is not uncommon for triangulation mechanisms to have this problem in them when processing n-gons shaped like that. Some algorithms tend to get led astray because those initial triangles seem nicely shaped, so it starts peeling away those but then ends up with a bad one at the end.

MoI's triangulator goes through some pains to not produce this kind of thing, so that's why you don't see the problem when you export using the Quads & Triangles option in MoI.

I have not reviewed your files yet to verify, but it is pretty likely that is your problem and the black shading is some side effect of the triangle being degenerate when it was created by C4D.

Tomorrow I'll double check your file to verify if this is the case or not. If it is, then I'm not really sure what I can do about it - it would really depend on C4D improving their triangulation mechanism to not create degenerate triangles in situations like this. I guess I could try to avoid creating this kind of shape, but that would probably mean slicing out points that are needed to make the polygon outline appear curved within the angle tolerance...

- Michael

Hi Michael,

sorry for posting here bit by bit, but i have to correct myself. The last to shots from the lefthand side and from the righthandside are both n-gons.
From one side the ngons are working correct. From the other side not.
Sorry, i`m really no expert here.
The other ways you`ve mentioned above don`t work for me. best thing is just to delete these points.
But if it is some Maxon-related problem i would like to tell them.

Greetings
Dirk

Hi Dirk,

> It seems Moi or c4d uses a whole triangle for the edge of the fillet.

MoI is making an n-gon there, there are no triangles involved at MoI's export time (unless you set that option of course) - it just happens to be an n-gon that has several points that are near to being colinear with one another as they follow some curvature.

C4D will take that n-gon and then break it into triangles for display and rendering purposes, and it's that triangulation process that is probably not going quite as well as you would want.

The way that would be good to triangulate it would be like this:



That gives triangles that kind of more gradually spread across the n-gon, instead of the previous case that I showed where you get 2 big triangles and one degenerate one. But unfortunately it looks like you are getting that bad case in C4D's n-gon triangulation.

- Michael

Hi Michael,

your were to fast with your reply ;)

If there is no workaround, i can live with that.
I would like to tell maxon about this problem, but i`m not sure if i can explain this issue well enough to them to make them understand.
Well, i will try it and direct them to this thread here.

Thanks for your effort Michael

Dirk

Hi Dirk, I took a look at your OBJ file, and it does look to be the problem that I was describing - the triangulation that C4D created is not so good and is following the example I showed above where it pulled out large triangles during the initial stages of the triangulation process and left a degenerate one along the side there.

Actually on the one side where it is showing black, I think that triangle actually got created in the wrong orientation, facing backwards - that's why it is black.


One workaround is to export from MoI as quads & triangles - that will end up using MoI's triangulator which won't do that.

I think it is also possible to manually edit the triangulation of an n-gon in C4D if you want to change how the n-gon is being diced up, there is something in C4D under Tools / N-gon Triangulation, I'm not quite sure how it works though.

One other thing to mention - it is pretty hard to see the triangle problem in an actual rendering, it is much more pronounced when you're zoomed in and looking with the real-time view.


I may be able to try and reduce the creation of this kind of shape in the future, but it is actually a proper n-gon, I mean it is not technically messed up or anything like that. It would be good if C4D would create a better triangulation for it.

It may be pretty difficult to describe this to Maxon, but I hope that the step-by-step triangulation illustration that I showed above may help...


Also, one other note - there is a setting you can tweak in the moi.ini file to change how MoI will produce a triangulation for things like that, by default it will do a kind of radial triangulation when possible, adding an extra point in the center of n-gons like that. It is possible to turn off that style and instead only use points along the outside of the n-gons, let me know if you want more info on that.

- Michael

Hi Dirk, just one other comment if you want to submit this to Maxon as a bug report, I would suggest deleting all the other polygons except for just one single one that has the black thing on it (but before yanking the points around), and then sending a file in with just that one n-gon in it as an example of the triangulation problem.

It helps a lot with bug reports to have the most simple data set possible that shows the problem.

It may not be a very easy thing to fix though, it can take a pretty big re-working of the triangulation mechanism to make one that does not back itself into a corner like this.

- Michael

If you're having problems getting OBJs into C4D, I recommend you try the RipTide plugin:
http://skinprops.com/riptide.php
http://skinprops.com/fr_rtdocs.htm

C4D is known to have quirks and limitations to its OBJ importer hence the reason why RipTide was created...

-Will

Thanks Will,

i`ve just tried Riptide, but unfortunately it doesn`t work in this case.
By the way, is it possible to direct someone directly to this thread?
The url in my browser just says: http://moi3d.com/forum/index.php?webtag=MOI


Greetings Dirk

vinced, middle mouse button new tab.

http://moi3d.com/forum/messages.php?webtag=MOI&msg=1620.1

~Danny~

Usually all the way at the bottom of the page there's an "All" link or "1-nn" link, those will also take you to the first post of the thread you're in. ;-)

-Will

Hi Dirk, also if you look in the upper-right corner of a message there is a link up there, like this one should say something like "1620.21 In reply to 1620.18"

Those little links are "permalinks" to an individual message, you can right-click on it and copy that address to the clipboard to give to someone else. If you want to give a link to the whole thread, go to the first message and grab it's permalink.

- Michael

"i`ve just tried Riptide, but unfortunately it doesn`t work in this case."

Sorry to hear it didn't work out for ya - Keith is presently tuning up his plugin and he's taking input from this thread here:

http://forums.cgsociety.org/showthread.php?f=47&t=624337

You may want to pop in and mention the problems you had or if you have some suggestions etc.

-Will