Basic 3D Modeling Concepts

MonkeyLek · March 4, 2003 9:19 am

In the real world, the art of sculpting consists in two main approaches: Remove matter. Add matter. In 3d modeling, you can work both ways, simultaneously! You can start with a basic shape and add details with geometry created apart using blend tools and remove geometry using boolean operations or trim tools. You can also give birth to new geometry from an existing one using tools like bevel, extrude, smooth shift and others. Each method has its own approach to create geometry. Graphic595.jpgGraphic594.jpgNURBS, or Non Uniform Rational B-Splines, are splines. They have "control points" located off the curve that controls their shape. NURBS also have edit points right in the curve, giving much more control. However, "edit points" are a curve tool, so once the surface is created you have only control points available. Surfaces in NURBS are defined with UV coordinates. A UV coordinate is an exact point in the surface. UVs are used to apply textures and insert isoparms on the surface. Isoparms are a visual feedback of UV coordinate and control points. They are also a great feature allowing you to easily add control points over the surface. The space between isoparms is the "patch". NURBS have the ability to create and edit curves. With them, you can draw profiles, surface them and precisely blend, trim, merge and match surfaces together in a very intuitive way. These surfaces have infinite resolution as well. Adding details in a NURBS surface is as tricky as it is with spline patches. You often end up with too many control points off the isoparm. so it is difficult to locate the right point. But, you can always create an object in NURBS and then move to polygon modeling to add details on the mesh. Mixing methods significantly speeds up production. Graphic597.jpgGraphic596.jpgPOLYGONS are used to create an object. Polygons are flat, so to create a smooth shape such as a ball or a human head, you would need a lot of polygons if we didnt have Subdivision Technology. Subdivision calculates a curve between the polygon vertices, smoothing the shape. If a vertex is close to another, it will have a "creased curve." Polygonal modeling associated to subdivision technology is good for creating low-resolution models which can later be converted into high resolution meshes. Low-resolution models allow you to add details to the surface quickly and but wont drive you nuts with a large number of control points. You can also concentrate detail in only a tiny part of the mesh to keep the poly-count low. Polygons are great for characters with many details but it lacks precision and infinite resolution curves. If you want to show a perfect sphere in your scene, and its made with polygons, dont get too close or everybody will see the polygons. SPLINE PATCHES are editable curves controlled by "control points" and handles. By moving the control points (located off the curve) you can deform the shape of the spline. The handles (or beziers) change the influence the point will have over the curve. It is a very intuitive method allowing you to draw the profiles of objects, then PATCH the splines to create a complex 3D object. A spline patch needs four intersecting splines and it is like a four-sided polygon except it is curved. For example, if you want to model an arm, you draw the profile sections and then you define cross section curves to create four spline intersections over the arm to patch it properly. Graphic599.jpgGraphic598.jpgAlthough you can create straight lines with splines, its main feature is the ability to create flexible and editable curves. Also, these curves have infinite resolutionno matter how close you get to the object, the curve remains smooth. Adding details in a spline patch mesh is more complicated than with polygons because any detail you add will be smooth too. When talking about wrinkles and bumps, smoothness is not what you want. It is not impossible, but you end up with thousands of control points, sometimes impossible to manage. UV mapping is one of the best ways to texture NURBS surfaces or polygon meshes. A UV map is based on UV coordinates which can be implicit or explicit: IMPLICIT UV COORDINATES - NURBS surfaces have implicit UV coordinates. A NURBS surface is a grid, where a set of curves running in an U direction intersects with another set, running in a V direction. Each point in that grid has its own and fixed UV coordinate. The texture you apply in this grid will follow these coordinates, implicitly. EXPLICIT UV COORDINATES - Polygon meshes are a free structure, created by 3, 4 or more-sided polygons. They dont need to be a grid to exist. Because of this, a polygon mesh uses an explicit, or assigned UV map. That means you determinate the UV coordinate of a point and apply your texture over it. Each approach has its use and its own set of tools to deal with and each software has its own tools and approaches to work with textures and UV maps.
Graphic587.jpg About loganarts: Loganarts' artistic career started at the early age of twelve by copying drawings from Todd McFarlane's Spiderman. Growing from these early drawings, loganarts moved on to attempt hyper-realism work as inspired by Ingres and Velazques. However, it was during his search for true self expression that loganarts returned to his naive style and was re-inspired by artists like Matisse, Schielle, Bacon and Freud. Loganarts' involvement in CG art was entirely brought on by pure need. Survival from producing traditional art in Brazil is virtually impossible. So, he bought a computer and started to sculpt, using tools such as Rhino. With the great help he received from people like Spike and Teyon (from Renderosity's Rhino Forum), loganarts was able to adapt his traditional art skills to CG quickly. After being active on the Brazilian CG scene for 2 years, loganarts has reached the highest point in his career so far - He was recently hired by the largest CG studio and finish house in Brazil! Loganarts will soon have his first motion picture FX credit! Loganarts' main goal for the near future is to work in personal artistic projects such as a short movie or a series of images representing his personal language to the world.
The Magazine Interact Forum's Back Room is the place to go for editorials, magazine excerpts, discussions, and plenty of surprises. Also, if you haven't done so yet, you can subscribe to the magazine or buy single issues. To find your way there, go to the Magazine Interact Forum, and click on the link to the Back Room at the top. Every couple of weeks, we'll be highlighting an article, review, or editorial from past issues of the magazine. Our second feature is an article from Issue #1, "Basic 3D Modeling Concepts." You can view this article in all of its original pdf glory by going to the Magazine Interact Forum Back Room and going to Special Features.

Article Comments


Guillermo ( posted at 12:00AM Tue, 04 March 2003

GREAT!! Thanks a lot Loggie ;-)

marinke ( posted at 12:00AM Wed, 05 March 2003

Okay! :) This is helpfull, like a guide you always keep by your computer, just to look when you forgot how it was again :) Thanks very much! -marinke-

Moebius87 ( posted at 12:00AM Wed, 05 March 2003

Very informative and a really good article, from one of the really good guys! Thanks very much, loggie. :o) - M

Mad_Wookie ( posted at 12:00AM Wed, 05 March 2003

Nicely written Loggie! Hope to see more of your stuff. MW

Renderbrant ( posted at 12:00AM Thu, 06 March 2003

Thanks alot Loggie :o) Very nicely done ;o)

loserbert ( posted at 12:00AM Thu, 06 March 2003

I'm always glad to see you post something loggie, it keeps us noobies motivated. By the way, is that a self portrait?

zapper1977 ( posted at 12:00AM Thu, 06 March 2003

really great i like it very informative thanks

billy-home ( posted at 12:00AM Thu, 06 March 2003

Cheers loggie, nice article matey