non-organic A chair...!

[veyron]

I'm fairly new to 3DS Max and doing 3D work in general, so I figured my first "real" project should be something nice and simple, yet something with potential if I wanted to take it further. Since I've always liked photorealistic interior renders, I decided to go for a common element in those - a piece of furniture. The simplest I could think of was a chair. I searched Google images till I found a suitable model (located here).

I then made some blueprints making heavy use of windows calculator (possibly overkill, but hey I'm a beginner)



I figured the hardest part of the modeling would be filling it out to look "plushy" so to speak, or billowy, or cushy, or pillow-like, whatever. Turns out I haven't even gotten that far before running into an issue =(

My problem is that I'm already getting mesh errors from this *really* simple model. They're only visible from certain distances when doing a clay render... But I'd still like to know why they're there and what I can do about them. I'm pretty sure it has something to do with the chamfered edges (I constructed the whole thing out of chamfer boxes so I wouldn't have to chamfer individual edges later)... What can I do?

The wireframe:


The problem:


Note that when zoomed in on one of the problem areas, the mesh appears clean. Also note that the middle two "cushions" are clean, while the back and side pieces have problems along their narrowest edges.

I also just noticed that the problem might only be when using a skylight, I just tried a direct spot and couldn't see anything wrong... might have been washed out though, and I'm definitely not going to test every single light in Max when I'm sure the answer is much simpler >_<

My guess? It's a bug relating to Final Gather/GI... No clue how to fix it though.

[geldslaw]

I'm curious to the type of texture you used to cover the chair, was it procedural or bitmapped? You identified a possible problem area, chamfered edges but noted that the problem didn't occur with the middle cushions.

One of the things you can do is to do a test render, that is, select a small area of the image to render befoer doing a final and complete render.

Try converting your boxes to editable meshes rather than just primitives, there may be more object property details available to the rendering engine to do the appropriate calculations for a complex object/simple structure?

hope that helpds

I'm sure the others will correct me if I'm wrong; but global illumination and final gather are only for calculating 1. highliight - light from a surface facing the source of light, 2. diffuse light, - all surfaces apart from black, unless black is under a reflctive surface like a varnish, will reflect light and finally 3. ambient light from surfaces in shadow and not in direct light, look at shadows in your room you can still see colour under the shadows are used to calculate light for photorealism.

[veyron]

The texture is the standard material, the only thing I changed was the ambient/diffuse color to something clay-like.

Converting between mesh/poly/patch didn't have any effect. You're right my initial guess concerning FG/GI is probly wrong... It really does seem to be the skylight. I'm currently just making do with different lighting setups with no problems... but its really annoying me that the second I add a skylight and press F9 there are problems.

[Jelmer]

hmm it may also depend on the renderer you're using, you can either use default scanline with advanced lighting>light tracer with the skylight you were talking about. Or you can use mental ray (which is far better, in my opinion, but a bit more complicated) with Final gather (FG) and optionally global illumination (GI).

I'm not sure if the skylight is causing the problem, you could probably fix it by just starting out with a box and chamfering that. Most of the time these errors occur when you have triangles or 5+ sided triangles with subdivision.
So if you use subdivision always try to have quad polys (4 sided, 4 verts).

Although i'm not sure if you're using subdivision already i do recommend it especially if you're going for for something like a chair which has many smooth, curved surfaces. I would get rid of the chamferboxes, make one box, delete one poly in the middle and apply symmetry. Because the chair is symmetrical it will save you a lot of work and you're sure everything is lined up correctly so it is actually symmetrical and not 'nearly' symmetrical.

You can chamfer edges by convering your box to editable poly and afterwards you can get rid of the triangles by cutting and welding vertices.
To make a side of a box bulge out a bit i would try to inset the poly and then move it out a little, then don't forget to apply subdivision either by using nurms subdivision from the editable poly modifier or by applying a turbosmooth modifier.

btw, it's good to create reference like that, it will save you a lot of time later on, because you're sure you have the right shape and proportions.

[geldslaw]

jelmer is right, I also tried repeating the process of using chamfer boxes but couldn't recreate the error using scanline or mental ray, but I'm using version 9 of 3ds max trial version, albeit a bit buggy its cool.

Ramplayer
you could also use the ramplayer, to do comparisons with renderings to see how the different settings pan out.
Scanline

Mentalray render

[CU441ES]

Or maybe for some reson the vertecies arent welded, thats happened to me a few times. /just pick a verted near the problem area and move it, if theres a gap the vetecies arnet welded, just use target weld to fix that

[veyron]

Recreating the artifacts: 1)new scene 2)create a box 3) create a skylight 4) zoom in on box to a view similar to the below renders 5) turn on Final Gather and render 6) view artifacts with a unpleasant expression on your face

At least that happens with my default settings, if your default settings are different in some way you probably won't see them.

I figured something out by randomly clicking things in the Final Gather rollout. Turns out that the problem had something to do with "Interpolate over X FG points", because when I changed it to "FG Point Interpolation over X radius", the mesh/lighting (don't know what to call them) artifacts disappeared. Just as a note, I started a completely new scene to test this, and the artifacts showed up on a primitive box (conversions have no effect), again with a skylight and FG.
Interpolate over radius:

Default FG points: (150 I think)

1000 FG points: (highest spinner will go)

I'm not really sure which is the most accurate, considering skylight conditions are unrealistic anyway... Soooo basically, I just have no clue what to make of those results. Any opinions or ideas?

Concerning the modeling:

Originally Posted by Jelmer

Most of the time these errors occur when you have triangles or 5+ sided triangles with subdivision. So if you use subdivision always try to have quad polys (4 sided, 4 verts).

Now that is an interesting piece of info, thanks. Uhhh, does that mean that I shouldn't have more than four lines connecting to a single vertex, or that all faces need to be 4 sided?

Originally Posted by Jelmer

Although i'm not sure if you're using subdivision already i do recommend it especially if you're going for for something like a chair which has many smooth, curved surfaces. I would get rid of the chamferboxes, make one box, delete one poly in the middle and apply symmetry. Because the chair is symmetrical it will save you a lot of work and you're sure everything is lined up correctly so it is actually symmetrical and not 'nearly' symmetrical.

I'm assuming you mean for smoothing; I was using NURMS subdivision at some points but not in the render provided. The smoothness increase was marginal and actually only served to throw off my alignments (albeit slightly). I will of course be smoothing once (if >_<) I get a working model..

Originally Posted by Jelmer

To make a side of a box bulge out a bit i would try to inset the poly and then move it out a little, then don't forget to apply subdivision either by using nurms subdivision from the editable poly modifier or by applying a turbosmooth modifier.

I just tried that, it works pretty well with ~2 render iterations and nurms subdivision. I'm a little worried about the creases that showed up, but I'll worry about that later I guess.

Here's what I have so far trying what Jelmer suggested; it's all a single ummm element, formed from a box with different segments and cut out to reach that shape. It does have the symmetry modifier so there is a seam going down the middle. The problem I think I'll be facing next is that I can't turbosmooth or nurms subdivide specific faces, and when half of it is smoothed and then mirrored, it looks ridiculous. I need the smoothing to leave everything touching the left side of the model completely alone on the X axis so the seams meet perfectly, is there any way to do that?


Sorry for the length, I've had this reply open for like 7 hours adding stuff to it...

[WolF]

I need the smoothing to leave everything touching the left side of the model completely alone on the X axis so the seams meet perfectly, is there any way to do that?

Actually, yeah. After applying a smoothing modifer (NURMS, Turbosmooth) select the vertices on the edge you need straightened, and just scale it on the X axis. That is 'deleting' the X plane for those vertices, therefor they are all lined up straight on one single plane. I don't know which plane those vertices are in, so just play with the scaling tool on different axis' for them. Hope this helps...maybe Jelmer or someone can explain better than I if it doesn't make sense.

[Jelmer]

hmm yeah wolf is right, that's the trick, but i'm not sure what you're problem is with smoothing, one thing that can cause problems is having polys on the actual line of symmetry (so on the inside of the model, you can't see them when the symmetry is on) the problem is, once you apply subdivision it will adjust the mesh to that so there's an opening in the middle, here's an image to explain it:

[veyron]

Ahhhhhhhhk. That should do it, thanks