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Michael Nicholson
Maya character building problems
on Nov 22, 2005 at 8:52:49 pm

Hi everyone

I'm ploughing through the book 'Maya 4.5 Savvy' and have arrived at the section 'Hands On: Building a Character 1 (Advanced)'. I find myself stuck at this point because I don't have much experience with Maya and find character building hard to grasp. The instructions in the book are very vague so I was wondering if there was anyone here who has read the book and could provide me with a few pointers on how to get through this section of the chapter (Chapter05)?

Any information would be most valuable. I would skip this section but I really do want to learn, so skipping it would be pointless.

Thank you in advance

Mike


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Sean Fennell
Re: Maya character building problems
on Nov 22, 2005 at 10:34:12 pm

I think I've looked through the book but I don't own it. Perhaps with a short background and the particular problem you're having we could still help out.


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Michael Nicholson
Re: Maya character building problems
on Nov 23, 2005 at 10:00:52 am

Ok, cool. Here goes;

The first instruction is;

1. Start with a sphere, with 14 sections and about 16 spans. Cut out the front-the front will be the mouth, and the back will be the top of the head. Shape the sphere into a rough figure of a human head as in Figure 5.51.

I guess what I'm really stuck on here is knowing what method to use to cut the mouth shape out and also any tips on editing the CVs to get the shape of the head. For example, are there certain groups of CVs I should move at any one time to keep the proprtions correct?

I've had a go at trying to replicate the images in the book but I can't seem to get the isoparms to follow the contours that they do in the image.

Hope all this helps and thanks very much again for your input. If all this is too vague and it's not possible to help then please don't worry. I'm sure I'll figure it out eventually.

Cheers

Mike


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Sean Fennell
Re: Maya character building problems
on Nov 23, 2005 at 5:55:01 pm

That's a perfect description. I fear I could write a book right here about what that book is telling you, and what any industry professional would tell you to do instead of what the book is telling you. I will Try to cover some main points for the example from your book, and then give you alternate techniques:

Usually when anyone uses "cut a hole" and "nurbs" in the same sentance they are referring to what Maya and other software calls Trimming. This is where you create a curve, project it onto the nurbs sphere, and use the Edit Nurbs -> Trim tool to create a fake hole in the surface. There are even a couple of ways to get the curve onto the nurbs surface for trimming, which are good things to know so I'll talk about both:

Projecting curves
1. With your sphere already created, create a Nurbs Circle.
2. Position the circle so it's facing the nurbs sphere where you would like the hole to be made. Like the picture.

3. Perform the Trim by selecting the curve and the sphere and using Edit NURBS -> Project Curve on Surface. This tool will project from a particular camera view, so you should look in a view that has your shape curve visible over the sphere (front view probably).
The curve will be built onto the NURBS surface:

4. This method of projecting will create a curve on the front and back of the sphere, so select the curve on the back of the sphere and delete it.
5. Now Trim the hole out by selecting Edit NURBS -> Trim Tool [options box]. There are few options but important ones. The Mode will determine whether the part on the NURBS surface that you click will be kept or discarded. Only closed curves on surfaces will create regions that allow you to designate to keep such a region or discard it. Leave it at Keep and click anywhere outside the circle shape on the sphere. Hit enter and you'll have created a hole in the sphere.

As you can see from my image, which has the CV's shown on the trimmed sphere , trimming nurbs geometry does not change the underlying CV distribution at all. This means that animating a mouth using this technique would be difficult if not impossible. You could animate the mouth using the circle curve that was used to create the trim, this is because the history is in tact and if you scaled or moved the curve right now (try it out) the hole on the nurbs surface will update to reflect the changes.

I'll show one more way to create that curve on the nurbs surface because the technique of getting a curve on surface is quite useful sometimes. Then I'll talk about the cons with the technique the book is trying to demonstrate, and some things you can do to make it easier:
1. In a new scene create a sphere and select it.
2. Click the Make Live button which looks like a magnet on the tool bar (next to the snap icons):
3. This will turn your sphere green and wireframe, this is live mode and it allows you to snap objects all over the surface of geometry. It also allows you to draw curves and, on NURBS surfaces, they will become curves on surface. Select Create -> CV Curve and start creating points on the surface.

4. You can use most Edit Curve tools on this curve, especially Open / Close Curve, which is usefull for creating a closed curve for trimming.
5. You have to deselect everything and the Click the Make Live magnet button again to convert the sphere back to regular mode so more modeling can be done to it.
6. Use the Trim tool as above.

Now that I've shown all that let me comment on this technique in particular and offer insight as to some other techniques. First thing, about technique, its always easier to draw up a character model sheet and bring Side and Front views, and bring them in as Image Planes into maya for modeling on. I'm not sure if the book shows how to do this, but it is the industry standard for modeling characters, even simple ones. Second, about the excerpt where the book says: "Start with a sphere, with 14 sections and about 16 spans", I don't agree with this, as do very little people in the industry. It's my opinion that working with less resolution to begin with and then adding spans when you need them is far more efficient and tends to lend higher quality surfaces that adding all the spans you think you might need at first and then having to deal with too many points. There's a NURBS modeling video from Alias called Nurbs Patch Modeing for Visual Effects which the instructor states this, then goes to prove how true it is.

The idea is to create the nurbs surface with the lowest number of spans possible to acheive the basic broad shapes and volume of the character. In addition you would place the detail on the geometry where the amount of curvature change is highest over the contour of your character. Hard to understand by me talking, so here's a simple image:

Please excuse the crap image that I drew with my mouse in about 2 seconds. But what I'm trying to illustrate is where large curvature change is. The spans that are Red signify where detail spans should be at a large curvature change in the character drawing. The blue lines are areas where there is very little curvature change, these blue lines you would not create as detail in your first blocking pass of adding detail. Other things that you don't put detail right away on is noses, ears, lips. Get the basic structure of the character's volume represented first. Then you can start adding the appendages. One more thing to note is how the red lines (and the blue ones) follow a flowing direction through the drawing. That is to say the span is oriented to the direction that the volume flows in the drawing. When modeling a character, if you keep all of your spans completely horizontal and completely vertical, you wont be able to represent the shape detail properly, and your deformations will fall apart later when you try to rig or animate. Model detail flow is very important!

Thirdly, and finally, using trims on any character is pretty much a no no. Especially in maya. Trims are just not efficient or easy to work with. Characters that have been made with trims will inherently run into some sort of functional problem, unless the trim is specifically art designed and technically designed into the model on purpose, you can be pretty assured that it will cause problems later. For rigid type of machinery and stuff that doesn't have to deform, trims are fine. But once you get that thing deforming, the shape is very hard to control.

Hope that helps.


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Michael Nicholson
Re: Maya character building problems
on Nov 23, 2005 at 8:27:15 pm

Thanks very much. That's a great help.

I'll get cracking on it and see if I can get this character built.

Thanks again


Mike


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