polygon edges appear smooth

# 1 20-04-2012 , 11:44 AM

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Posts: 13

hi guys,

i have a problem: i'm modelling a car at the moment, i built the rough surfaces in nurbs and then converted them to polys. sometimes a strange thing happens: after i combine two patches and merge the verteces together, the edge is rendered smooth in the viewport. in the pictures below, you can see that sometimes it only appears partial as well... i know it has to be a problem with the normals, because when i average them, everything appears smooth, but thats not what i want...the face normals all point in the same direction.

do you have any clue? maybe its a stupid problem, but i'm quite new to maya...

thanks a lot!

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# 2 20-04-2012 , 12:43 PM

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Join Date: Feb 2004

Posts: 2,988

Hi poogle,

Is this for a game? If it's for a high resolution render, you'll want to put tight bevels on the areas that you want to keep sharp, then smooth your object.

If it's for a game, you can automatically make certain edges over a given angle hard. Go to Normals>Set normal angle, and play with this value. Looking at your image, I would start around 50 degrees.

Imagination is more important than knowledge.

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# 3 20-04-2012 , 12:53 PM

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thanks for your reply!

the model is for design visualisation purposes... the next step would be to insert edge-loops to the edges that should remain tight. the problem is, that the viewport doesnt show smooth mesh preview but normal polygons...and also i didnt mess around with subd proxy or anything like that. plus it only concerns some edges, not all. then why are these edges smoothed out in the viewport?

appreciate your help!

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# 4 20-04-2012 , 01:00 PM

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It doesn't show smooth mesh preview? Have you tried pressing 3 on the keyboard?

Imagination is more important than knowledge.

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# 5 20-04-2012 , 01:04 PM

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thats exactly the problem, i'm sure it doesnt, because i switch back and forth between 1 and 3 to check the surfaces. and some of the edges do appear hard, as they should...if i press 3, it gets even smoother...

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# 6 20-04-2012 , 01:26 PM

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Of course, because the edges with the hard normals are creased in smooth preview, and the one's that aren't are smooth.

I wouldn't worry about this until you get further along with the model. Playing with normals while modeling is usually a waste of time. I model about 90% of my stuff with every normal set to hard, as then the normals don't distract me.

Imagination is more important than knowledge.

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# 7 20-04-2012 , 01:54 PM

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if that just affects the way it is displayed in the viewport and i can change it at any time, then i can live with it...it just makes me feel insecure, i always think it has to do something with the geometry itself, because it only happens in some parts and not the whole model.

makes me wonder, why this happens...i'd rather know the real reason for this and how i could change it.

anyway, i'm very thankful for your support!

if someone else has something to contribute, it's still welcome...

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# 8 20-04-2012 , 02:03 PM

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Edge normals (hard and soft) should have absolutely no effect on smooth preview mode. When you switch to smooth preview mode (3-key) ALL the edge normals are softened and the model is subdivided 2 times (by default).

So there is no creasing as a result of hardened edge normals. The only reason edges would appear sharp would be if surfaces have reversed normals, there are co-resident edges, or other non-manifold geometry.

Do the following things...

First just simply harden all the edges (select the object and normals > harden) so in unsmoothed mode you can see all the faceted poly edges and all the open gl shading artifacts will go away. I hate modeling with softened edge normals because you get all kinds of open gl render artifacts and it's hard to visualize the actual poly surface.

Then do the following things...

1. Under lighting uncheck two-sided lighting. All surfaces with reversed normals will turn black.

2. Go to display > polygons > soft/hard edges. This will display softened edge normals as dashed lines and hardened edge normals with solid lines. Once again edge normals do not affect edges in smooth preview mode.

3. Go to mesh > cleanup and fix non-manifold geo, faces with zero surface area, and edges with zero length.

If you wish you can save the model out as a .ma change the .ma to .txt and upload it and I will be happy to look at it.

When merging poly surfaces Maya will always soften / harden edges in the combined parts using the default 30 degree angle to determine whether to soften or harden an edge normal. I like to keep the normals > harden, soften, and set angle tools on my shelf and harden all the normals as I am modeling so I can see all the poly edges clearly as I model.

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Last edited by ctbram; 20-04-2012 at 02:58 PM.

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# 9 20-04-2012 , 02:40 PM

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By the way the reason you are seeing some edges hard and some soft in unsmoothed mode (1-key) is that maya applies a 30 degree smoothing angle to the object when you combine poly surfaces and so some edges are getting softened.

However the default poly edge display mode is standard so you see all solid lines when you look at the wires and the open gl renderer displays all kinds of shading artifacts. This is why I harden all my poly edges as I am modeling.

Hardened edge normals will not cause creasing when you go into smooth preview mode because all the edge normals are softened after the model has been subdivided 2 times. So the only creasing will be as a result of either bad geometry or edges that are very close together.

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 20-04-2012 at 02:45 PM.

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# 10 20-04-2012 , 03:06 PM

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ok, that gets me closer...but i dont quite get it.

- when displaying soft/hard edges it is true, the soft edges are dashed (nearly all of them, just not those that were the edges between two merged patches)

- shouldn't polygon edges be hard by default?

- if i select the whole patch and go to normals -> harden edge it works, but the whole thing looks even "harder than normal", it looks as if you turn on flat shade all only for this particular part...

but as long as it has no effect on the final result, it doesn't bother me that much.

really, i appreciate your help guys!!!

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