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View Full Version : The Bane of my Existence: Non-Planar Poly's



AmbientRevo
05-08-2010, 04:02 PM
I enjoy sub-d modeling, however lately, I have been doing a large polygon modeling project. It is reaching 200,000 polygons in total, and I have come across many non planar poly's that seem to pop up even from performing the simplest of operations (move, stretch, etc.)

Often times I can get rid of the polygons by cleaning the mesh better, lining things up, etc. Sometimes I have to resort to Tri-ing the offending polygons in order to remove render artifacts.

The following is the result of a simple stencil on a surface, then multishifted in:

http://img341.imageshack.us/img341/10/screenshot20100508at307.png (http://img341.imageshack.us/i/screenshot20100508at307.png/)

after tweaking the non planar poly on the right, I was able to eliminate this problem, however now i require a smooth shift operation at the bottom polygons of the following mesh:

http://img707.imageshack.us/img707/8632/screenshot20100508at359.png (http://img707.imageshack.us/i/screenshot20100508at359.png/)

As you can see these non planars are on an angle, i produced them simply by moving down the end vertices, How can I go about solving this problem or do I have to resort to the ugly tri method again (most likely will make UV'ing absolute hell)

Thanks for any advice :)

-AmbientRevolution

Exception
05-08-2010, 05:41 PM
That's a puzzle. In fact, I'm quite surprised you're getting these non planars so easily. I wonder if you've hit some odd condition where modeler's not actually being as precise as it should. Are your objects very big with tiny details or something? You might be running into some float rounding issues.

In any case, I don't know if it's much help, but there's the flattener tool on the detail tab, that might help flatten some amount of your non planars in some cases... there might be a plugin on flay that does this a bit better... hmm... will check.

Salv8or
05-08-2010, 06:15 PM
I always try to model things without getting in to thouse situations. Trying to keep things as quads as far as you can is always the simplest way, at least in my experiance.
Would it be very excpensive for you (polygonvise) to make that bevel to consist of only quads? (select 2 points where you want an edge and hit "ctrl+L)
And use "add point" tool if you to add a point on a edge, if you dont have a enought points to connect up to a quad.

And as Exception says, if its a very large object modeler looses the precision. To prevent that, if possible make a piece of that perticular part and center it in modeler and move it to the correct position in layout.

Hope it it helped you on your finalizing.

probiner
05-08-2010, 07:09 PM
Ways to get around non-planar issues, in order in order of easiness:

1-Normal Corrector LScript. Select the Non-PLanar polys, run the script and voilá, it tells you how many it corrected.
http://www.lwplugindb.com/Plugin.aspx?id=20e5fbf4

2-Triple them, merge them back

3- If there is one really stubborn you can go with cplane to crush the points into the plane. http://www.ats-3d.com/cplane/cplane.htm
http://i153.photobucket.com/albums/s202/animatics/Lightwave/cplane_exp.png
Cheers

AmbientRevo
05-08-2010, 07:32 PM
Normal Corrector did nothing, in fact if I run it on this part of my mesh it ADDS a single non-planar to it.

Trippling and Re-Merging does nothing.

Haven't tried the last one yet.

To put this in perspective, My entire mesh is 200,000 polygons, 30,000 of which are nonplanar.

I've gotten none planars from operations simple as rail extrude. To tiny little cubes with just a few small vert tweaks to them. However so far it has been rendering fine, this is the first time i've had serious problems with this.

Thanks for any additional help you can give, more pictures will be up soon, to show my problems.

-AmbientRevolution

probiner
05-09-2010, 06:10 AM
AmbientRevo

Those tips were not to make them planar. But to correct the normal which is what normaly gives issues in render time ( which i thought it was your problem in the first post).

Non-Planar polys will happen all the time with mesh editing. They only become annoying when the normal is badly calculated, resulting in some unexpected results with a modeling tool or in a render.

So run Normal Corrector again, make a render and if it renders fine you don't need t worry about having Non-Planars in the model so much, because from what you shown, they are not that steep non-planars.

If you want you can handle me a model and i'll se what i can do about reducing the non-planars.

Cheers

PS: Flatten is nice, Exception, i forgot about this one. But if the normal is wrong so it will be the flattening operation. So Normal Corrector and then Flatten work nice.

BeeVee
05-10-2010, 01:12 PM
Also, if your final destination is SubDs as you state in your opening post, then you don't really need to worry about non-planars - the amount of twisting that you apply to control points to make SubDs sharp enough can often result in non-planar polys, but it doesn't matter so much as soon as you hit TAB...

B

david_scotland
05-30-2010, 01:24 AM
Also, if your final destination is SubDs as you state in your opening post, then you don't really need to worry about non-planars - the amount of twisting that you apply to control points to make SubDs sharp enough can often result in non-planar polys, but it doesn't matter so much as soon as you hit TAB...

B

I agree with this, TAB to sub-d and all non-planar polygons vanish.

cresshead
05-30-2010, 03:16 AM
looking at the example image there's no way he'll hit TAB right now...it'll just go to mush if he does...

simple fix is just to trianglulate it...

Captain Obvious
05-30-2010, 06:20 AM
Okay, first off, let me point out that I've done significant amounts of research regarding Lightwave's ability to rendering different kinds of topology.


edit: that render error in your first post is from a concave n-gon.

As long as a polygon has four sides and is not massively distorted, Lightwave will render it fine. A four-sided polygon that's any sort of shape you could achieve by holding a rectangular piece of stretchy cloth will pretty much always render fine. If it's horrendously nonplanar or concave (http://en.wikipedia.org/wiki/File:Convex_polygon_illustration2.png), it might still cause problems. But generally, anything that's roughly rectangular in shape and has four sides is fine. Don't worry about it.

Polygons with MORE than four sides are fine, as long as they are reasonably planar AND convex (http://en.wikipedia.org/wiki/File:Pentagon.svg). A concave n-gon will usually render fine as long as it's perfectly planar, but the more non-planar it is the greater the risk of it rendering like a miserable mess.


Triangles always render "fine," but Lightwave tends to produce smoothing errors on triangulated meshes, and they use more memory and take longer to render than n-gons and quads, and it can be tricky to perform modelling operations on triangles.


So, to sum things up:

1: Use quads as much as is practically doable.
2: If you have n-gons, then manually split it up into convex quads.
3: If you have heavily distorted quads, try to change the topology by rotating edges and the like so you end up with nice quads. Here's some examples: BAD (http://dl.dropbox.com/u/3149840/random%20stuff/NTForums/Topologylessons/Quads/bad.png) and GOOD (http://dl.dropbox.com/u/3149840/random%20stuff/NTForums/Topologylessons/Quads/good.png)

GraphXs
05-30-2010, 08:41 PM
I say go the Sub-D route. Even try using CC's with edge weighting CC's allow for n-gons. (make sure ya only edge weight after your happy w/the base mesh) Or if ya model with quads and LW's normal sub-ds. Add a lot of tight edge loops to the mesh. (look for TrueArts swift edge loop tool, works great for adding/editing/removing edge loops.

Good luck!