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yakul
03-04-2007, 07:15 AM
Lets say I model a mesh with MetaNURBS or SubDivide.
Now I have the NURBS form of the model (before I subdivide it), and I want to add to the model some bumped lines/curves/stripes.
However, it is a difficult task to achieve, because I might ruin the flow of the model when suddenly adding to a big triangle some very small and detailed triangles to model the bumped line.
Also, all sort of hazards may happen.
I think that just knifing the model and then smooth shift the stripe is not very good. I wont get a nice flowing curve.
If you didnt understand, I want the stripes/curves to be modeled in the geometry and not by a bump map texture.
Do you have any suggestions on how to achieve this?
I work with lightwave.
Thank you.

glib
03-04-2007, 07:30 AM
I'm not sure I follow, the language barrier is getting in the way. I think you're saying you have a nurbs surface, and you want to model stripes on it, but don't want to have bad edge flow after you convert it to sub-d? Use separate objects for your stripes, move an isoparm to where you need it on the surface, extract it to a spline, create the profile of your object and birail it.

yakul
03-04-2007, 08:21 AM
I'm not sure I follow, the language barrier is getting in the way. I think you're saying you have a nurbs surface, and you want to model stripes on it, but don't want to have bad edge flow after you convert it to sub-d? Use separate objects for your stripes, move an isoparm to where you need it on the surface, extract it to a spline, create the profile of your object and birail it.
What is an isoparm?
Do you mean that I will create the stripes seperatly, by first drawing splines and then using rail extrude or something similar on them?
Ok, now I have the stripes. How do I connect them to the main mesh?
I dont want to just copy paste them into the mesh, because they need to be smoothly merged into the mesh.
Or did I not understand your explaination?

kirigoi
03-04-2007, 10:57 AM
Hi glib!

Yakul, an isoparm is a term used when NURBS modelling in a NURBS package like Maya. It is analogous to an edge in SubD surface modelling. Lightwave does not use NURBS surfaces however (it has good SubDivision Surface capabilities, but they are not the same thing), so you might have problems doing what glib suggests as there is no easy way to cut a curve into Lightwave subPatches. Lightwave's MetaNURBS surfaces are rather badly named as they don't really do the same thing as what other people would refer to as NURBSs.

The problem with incorporating small pieces of geometry into a curved surface is that you need to create a flow of edges around the object you want to create, then incorporate this into the larger mesh without introducing pinching from having too many non-planar polygons or points radiating too many edges (called high-valence vertices). Can you show a screenshot of what you want to achieve?

http://www.skylight3d.com/images/CGTalk/screens/curve_vents_03_B.png


One of the general techniques I use most often use is to create the detail and position it in the right place. Then I extend an edge out from the sides of the detail geometry (so that I have an edge loop around the detail) and work this into the original piece. This isn't always necessary as sometimes it's easier to build the detail by adjusting and extending edges on the original mesh. It's something of an artform to know how best to create topology that does this correctly, but if you post a screenshot of what you're trying to achieve I might be able to give more specific hints. I've already done something similar here (http://forums.cgsociety.org/showthread.php?p=4084114#post4084114)to show how to cut holes into a curved surface like the one above.

There's also an interesting thread here (http://forums.cgsociety.org/showthread.php?p=4084089#post4084089) that discusses many of the problems you're suggesting, for example, here's a pic of a way of incorporating a sharp rectangle into a sphere. Note the way I've kept an edge around the detail, then worked this into the sphere polygons.

http://www.skylight3d.com/images/CGTalk/screens/edgeloop08.png


Here's a couple of other basic examples:

http://www.skylight3d.com/images/CGTalk/screens/edgeloop01.png



http://www.skylight3d.com/images/CGTalk/screens/edgeloop02.png


Again note the edge loop around the detail. This allows the surface to curve smoothly into the detail and not pinch.

I've been meaning to create a Subdivision surface primer as many of these questions come up quite often, but there are plenty of tutorials if you know where to look. Feel free to ask more questions about your specific example, but I'll probably need a bit more information to know exactly what to suggest.

M

yakul
03-04-2007, 12:46 PM
Thank you mark, your post contained valuable information for me.

Unfortunently, I do not have a copy of lightwave on my computer. But I will soon have.
And when I do, I will revive this thread and post what I want to do.
Thanks.

newellteapot
03-05-2007, 08:55 AM
Yakul, Hi!

I'm a poly enthusiast, try and use polys instead, they make your life simpler :)
Hope this helps :)
Please don't hesitate to drop me a line or write here again for more information.
Monica

yakul
03-05-2007, 09:20 AM
Yakul, Hi!

I'm a poly enthusiast, try and use polys instead, they make your life simpler :)
Hope this helps :)
Please don't hesitate to drop me a line or write here again for more information.
Monica
I am sorry, I dont understand what do you mean by that?
What do you mean use polys instead?

yakul
03-07-2007, 07:44 AM
Double post

yakul
03-07-2007, 07:44 AM
I am sorry if bumping this thread is not appropriate.

I have installed lightwave9 trial and created the model I have planned.
I have also created splines which represent the stripes I want to add to the space ship.
My question is how to add these stripes to the space ship before the subdivide, so that the stripes will integrate smoothly into the model.
I have another question, since this is going to be a model in a game, I would like to know how should I create the low poly of the model. The model that its geometry is actually going to be used in the game. The high poly is going to be used for the normal map.
Here are the images:

http://img206.imageshack.us/img206/985/stripesmetaia3.jpg

http://img148.imageshack.us/img148/7734/stripesjy8.jpg

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