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View Full Version : How do I get rid of this artifact?!



VWTornado
04-09-2003, 10:51 AM
I am modeling a bunch of characters for an animation and game I'm making. Everything looks good except I keep getting this artifact when using Balls and then hitting TAB to make them subdivision surfaces. :(

Here's a simple example of what I'm talking about:

http://vwtornado.baked.net/PICs/Artifact.jpg

And a Close Up of what I'm talking about:

http://vwtornado.baked.net/PICs/Artifact_CU.jpg

mfegley
04-09-2003, 12:14 PM
that's caused by 3 point polys being nurbed. to smooth it out a bit, you can "merge polygons" by selecting 2 of the 3 point polys and making them in to 1 four point poly. the "bumps" will be less apparent. BUT, to get rid of it, create your characters by creating nice bands of 4 point polygons. that's the only real way to get around it. i'll do a little test to try and explain myself.

mfegley
04-09-2003, 12:42 PM
ok... here's my example. mind you, it only took me a few minutes (while at work!:D ) to show you what i mean. i know its not a perfectly round circle but it could be and not give you lumps. theres a total of four 3 point polys so it keeps it smooth. try it out. it may work for you. but, if you need it to be a perfect sphere and really want to go the other route, make that the top of the head and slap some hair on! pretend it's his soft spot or something!

ChandlerL
04-09-2003, 12:45 PM
If poly count isn't a concern (and mfegley's advice is great), here's another option.

Tesselate the ball (triangles) rather than the default quads/triangle mix. (When creating the ball, hit 'n' to bring up the numeric panel and click the Tesselation button)

Here's a tessalated ball prior to subpatching (Tab key)
http://www.myny.us/Tessalatedball.jpg

...and with subpatching (Note no smoothing artifacts)
http://www.myny.us/Tessalatedball_sub.jpg

...I still think mfegley's advice is better, though (Less polys)

Elmar Moelzer
04-09-2003, 12:50 PM
Make a segmented cube and use spherize to turn it into a sphere that will subpatch without any artefacts.
CU
Elmar

VWTornado
04-09-2003, 12:54 PM
poly count really isn't a concern here. they aren't gonna be THAT complex, not near as crazy as some of the stuff i've seen on this and other 3D forums. to give you an idea of what one of my characters looks like here is a shot of the players character in the game. (the reason poly count doesn't matter to me is they are all being rendered to 2D images for use as sprites in a 2D game making program.

http://vwtornado.baked.net/PICs/Robot_Render2.jpg

He isn't done, needs textures and some little detail, but this gives you a good idea.

VWTornado
04-09-2003, 01:00 PM
Originally posted by Elmar Moelzer
Make a segmented cube and use spherize to turn it into a sphere that will subpatch without any artefacts.
CU
Elmar

See, the problem with the suggestions so far is you are assuming I am just modeling a perfect, simple sphere, which isn't the case. I posted one of my characters above so you could get a better idea of what I'm doing. The problem on this model is on the front of his mask between those 2 breather tubes. thats where I'm getting that weird artifact on this one. same problem with all my other models so far also, wherever the sphere comes to its point is where it happens. is there any other way to do this w/o remodelling the parts that are getting the problem? that would be really discouraging if i have to start over. :(

heres a view of the character from Lightwave:

http://vwtornado.baked.net/PICs/Robot_Hero.jpg

ChandlerL
04-09-2003, 01:03 PM
Originally posted by Elmar Moelzer
Make a segmented cube and use spherize to turn it into a sphere that will subpatch without any artefacts.
CU
Elmar

When you spherize it, how can you be sure to get a sphere rather than something that resembles a square capsule?

Creating a square box then spherizing gets me this:
http://www.myny.us/capsuleeffect.jpg

ChandlerL
04-09-2003, 01:04 PM
VWTornado,

Did you try the tessalation idea? I noticed that you weren't creating a perfect sphere which is why I provided an example using an imperfect tessalated sphere. (it's thin like yours)

Re-shown here:
http://www.myny.us/Tessalatedball_sub2.jpg

mfegley
04-09-2003, 01:07 PM
well, honestly, i can't see the artifacting in the image you posted so... unless you are going to have it real close, i don't see a problem. also, if he will be textured, that leaves even less worry! my only suggestion from here on would be to stay away from spheres and cones and such if you are going to nurb them or use it for characters. i tend to build with boxes or create polys by placing points. use as many 4 point polygons as possible and keep the tri ones AWAY from each other!

your dude looks good, man. keep up the good work!

robewil
04-09-2003, 01:22 PM
Guys, Here's what I believe is the best way to approach this:

Start with a disc.

http://www.legal-lgt.com/SpSphere\SpSphere01.jpg

Select the points on the right side without including the top and bottom points.

http://www.legal-lgt.com/SpSphere/SpSphere02.jpg

Delete the points leaving a semi-disc.

http://www.legal-lgt.com/SpSphere/SpSphere03.jpg

Move the object 1mm to the left

http://www.legal-lgt.com/SpSphere/SpSphere04.jpg

Use the Lathe tool and rotate the object around the Y axis at X=0, Z=0. for -360 degrees

http://www.legal-lgt.com/SpSphere/SpSphere05.jpg

Select and Delete the polygons that are vertically along the Y axis.

http://www.legal-lgt.com/SpSphere/SpSphere06.jpg

At this point, all polygons are 4 sided. Press the Tab key.

http://www.legal-lgt.com/SpSphere/SpSphere07.jpg

VWTornado
04-09-2003, 01:25 PM
thanks.

you can see the artifact up close...i dont have the model here at work so i can't post a close up right now. but one of my other characters shows the artifact pretty bad up close...luckily for the game they are only gonna be like 100x100 pixels at most, so you won't see it there. But I'd like to animate them also, and that means some possible closeups. Plus it just bothers me not knowing why its happening. And I hate using triangles for modeling, it just seems old school to me. :D But if that fixes the problem then so be it, I'll use triangles! (or whatever i need to for the models to look perfect)

VWTornado
04-09-2003, 01:34 PM
robewil, doesn't using the lathe tool like that still cause the same triangle/square polygons that just making a Ball does? :confused: could you render a closeup of the tip of the ball where its coming to a point, with subdivision turned on?

robewil
04-09-2003, 01:42 PM
If you follow my instructions, they are all 4 point polygons. The key to this is the 4th step of moving the object slightly off the center but lathing it around the center. Yes, it's a slightly imperfect sphere this way and you could probably move the object less than 1mm and get an even more perfect sphere.

Here's the closeup of the top.

http://www.legal-lgt.com/SPSphere/SpSphere08.jpg

Elmar Moelzer
04-09-2003, 01:44 PM
ChandlerL, here is a step by step- tutorial especially for you.
Create a box like this:
http://www.mediastudio-graz.com/images/spherize_tutorial/box_sphere1.jpg
When you hit the spherize - command you get a sphere like this:
http://www.mediastudio-graz.com/images/spherize_tutorial/box_sphere2.jpg
VWTornado, here is what I would do(not seeing where the artefacting is exactly at the moment): Either simply merge the traingles 2 by 2 until they are all quads. Then some spin- quads might help to get you further. Or go out of SP- mode for the part that is causing trouble, merge all triangles so that you have got a flat plane at the end. Then use a bevel with a small shift and an inset big enough to get an aproximation of the bulge at the end. You can do this a few times until the disc at the end is so small noone is going to see artefacts anymore (though to be honest I dont see them now). Then simply collapse the disc, Subpatch again and you are done.
Hope that helps.
CU
Elmar

ChandlerL
04-09-2003, 01:51 PM
Aaaaaah. Of course, of course. I was hitting right arrow and up arrow to increase the segments and completely overlooked the amount of my Z segments. doh!

Thanks for the insta - tute, Elmar! :)

VWTornado
04-09-2003, 02:42 PM
elmar, how to I merge the triangles to make them squares?

thanks

Elmar Moelzer
04-09-2003, 03:33 PM
Select two adjacend triangles and hit [Shift+z] or [Z] to merge them.
CU
Elmar

VWTornado
04-09-2003, 04:08 PM
elmar, i tried merging the triangles and it reduced the problem by half, but the artifact is still there. looks like that tessalation idea when i create the original sphere is the way to go. thanks for the help. i wish i could fix his helmet though...i really dont wanna model that again.

woah, i just tried the idea of making a segmented cube and spherizing it, that works pretty well also. thanks everyone! just sucks that ill have to remodel parts of the characters, oh well...i want them to be good, so ill take that time. :)

Elmar Moelzer
04-09-2003, 04:41 PM
As I said you wont need to remodel it. I mentioned other techniques to get by the problem. You could also select all triangles and smoothshift them, then scale them down, making the artefacts smaller.
CU
Elmar