3d Modeling

[george]

Is there some sort of introduction to "polygonal modelling", or "wireframe"? Maybe even a simple book. I've downloaded the trial version of Silo. I'm definitely a beginer(although I've been interested for years).

[dana_swift]

George- look in the books written for 3D computer game programming. I suggest you do this at a bookstore, as 95% of the books have no useful information in them.

You might learn all you want to know while standing there and thumbing the chapters, and may save the cost of the book.

3D modeling is rarely based on polygons.

3D models are usually made in one of several ways:
1) Topographical relief.
2) Geometric shapes
3) Triangular fascets
4) algebraic models (bezier and nurbs)

The topographical relief idea is the "altitude" of a surface is specified in a grid of X-Y points. This can only represent one surface of an object, but for relief carvings that is all that is needed. This method is used in Autocad for "mesh" defined surfaces. Other programs call this method "surface maps".

The geometric shapes method (like sketchup) allows simple shapes such as boxes and cylinders to be added and subtracted (drilled out) of each other creating very complex shape definitions. Languages such as VRML are often used to specify models built from these concepts.

The ultimate definition of a surface can be broken down to little triangles in space called fascets. Each fascet has a "front" and a "back", so logical concepts sucha s "inside" and "outside" are defined. However triangles in space do not represent curved things well, so the solution is to use LOTS of them so the approximation of the desired surface is close enough for the application. This is the method used with point clouds. Files such as STL use this method, but get HUGE to represent a complex object.

The algebraic method is manipulated with graphics saving us poor humans from having to do all the underlying math, and can define elegant smooth curved surfaces. The method was created by a mathematician named Pierre Bezier who needed to define the shape of a Renault automobile so early NC machines could be used to cut the shapes. What he did was come up with a method of describing shapes that artists could understand, and computers could easily convert to toolpaths. This method is so popular it has spawned many "improvements" including nurbs, splines, bsplines, and the entire family of Bernstein polynomials.

Commercial 3D modeling packages support some combination of these methods and sometimes others. Each one favors one method over another, and usually can generate topo models, or fascet models.

Once a geometric primitive or algebraic model has been converted to topo or fascets, it is very difficult to be converted back, often impossible.

Whatever method a given software package uses internally to represent the object being modeled, they usually convert the model to the fascet representation for toolpathing by some external software package.

Some packages generate toolpaths directly from algebraic or geometric models, as they give the highest quality results, but cost the most money.

George, the only difference between a beginner and an expert is the point at which they become confused!

Good luck-

D

[acb]

Great little overview, Dana!

[george]

Dana, I'm off to the bookstore and the public library. I'm a cartoon fan, by the way. I want to learn how to turn what I design in the "real" world into files. I would never model a chair seat without carving it first. I could measure that. I also picked up the term "polygon mesh" from the Wikipedia. I designed and built this chair with my crude CNC education in mind. I don't see how it could be produced any other way. Hope this helps explain my intentions, and thanks.

Contemporary Windsor Chair

Contemporary Windsor.psf (45.2 k)

[myxpykalix]

Here is some elementary 3d instructions and some of it is specific to lightwave but if you get to the part with "Lightwave modeler" it should start off with some elementary stuff. Much of it you can skip because these are most surface attributes that we aren't concerned with when creating our 3d objects like color, luminosity, duffusion, tranlucency, reflection, ect.. You could google "3d tutorials" and you will find more info online that will be appropriate for you than going to the bookstore.
I get a newsletter for DAZ (although i have never really checked it out) some of the models (human figures) look like real women and men and some of the architecture pieces (buildings) look almost like a photo the are so realistic. That might be a more up to date and easier program to make use of for your purposes. What file format it outputs I don't know but its worth a few minutes looksee:
http://www.daz3d.com/

http://www.lyzrdstomp.com/index.php?...&Itemid=86

[Forum Admin]

Windsor chair image

34512.jpg

[bill.young]

There have been a lot of postings recently about using Sketchup to design and model Windsor chairs on the "Design, Click, Build" blog on the Fine Woodworking website.

http://blogs.taunton.com/fw-designforum

Bill

[george]

I've made templates for everything, including the turnings(I'm a copy lathe operator). The seat takes me twenty hours. I think I'll find a faster way when I call about Shopbot training.

[myxpykalix]

George,
I know i have seen a dxf somewhere of a windsor chair and seat, the profile of the seat part was something i recall as being specific. Maybe it was just an article i was reading. The whole idea is obviously making it in 3d to cut on the bot so you don't first have to hand make your "master".

[george]

Mr. Jarvis, you strike a note. I didn't ask the right question. My chair took over two years, and multiple prototypes. It is the result of a lot of feedback from my suffering friends and family - and now the patient Shopbot forum as well. I have to face up to getting my feet wet, and jump in to the CNC thing. Incidentally, the chair was my primary effort for this year's International Contemporary Furniture Fair.