Is SolidWorks really a solid modeler?

I have been teaching Computer Graphics this semester. I am using Bertollini's book which might be a very handy reference to have around if you can afford it. He has a listing of all possible graphics types of which a very small group is called solids. Aside from prismatic solids the other major group consists of things like tetrahedra, dodecahedra (based on the pentagon), icosahedra (based on the triangle), etc. I have never found it easy to model these solids in SolidWorks or any other solid modeler because they tend to work off of sketches.

Perhaps we should call the current crop of software Prismatic Solid Modelers or Bounded Volume Modelers instead.

Reply to
P
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How about "Sheet-Knit one, Pearl two" software. Heh, just kidding!

Mike

Reply to
Mike J. Wilson

Is SW a solid modeler? If it isn't, then nothing is. If the book is about computer graphics, then the focus would likely be more on rendering, not on modeling.

This goes to the heart of the question: "What is a solid?". One math professor told me the difference between a solid and a closed surface boundary is that the solid has normals defined for all of its faces that are all in the same direction relative to the enclosed volume.

In previous jobs, I did plenty of CAD modeling that was not "feature based". It was all knitting and trimming of sculpted surfaces into solids. Sometimes the surfaces were parametrically controlled, sometimes not.

Reply to
That70sTick

Volume definition with a density attribute gets my vote. It is sort of interesting, void lumps and all.

Bet if you look around a bit you can find someone that thinks there's something inside the "solid". (Wul, 'course there is. Just bore a hole thru it. See?)

8~)
Reply to
Jeff Howard

Before I started teaching the class I was pretty much of your opinion. Funny what a change a little reading can do. I am speaking from Bertollini's classification system. Different people classify the kind of stuff we construct in different ways. I have posted the chart of which I spoke at:

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What I am saying is that SW is limited to a certain class of solids called prisms and knit surfaces. Regular solids and pyramids take special effort to construct and some types of regular solid are extremely difficult to construct even though they have all flat faces. The kinds of solids of which I speak are the ones the Greeks wrestled with thousands of years ago. See:

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Try to make some of these things and see what happens. I have frequently run into dead ends.

Even some of the warped surfaces in this classification are a bit of a trick.

Patran 2.5 was a real solid modeler in that it not only defined the outer surface of a volume, but every point inside. Patran 2.5 was designed for creating finite element models where it was necessary to know something about the inside.

Bertollini, BTW is a book on drafting, but he calls it by the fancy name "Technical Graphic Communication" in order to encompass the broader range of uses that companies with products like SolidWorks engender.

Reply to
P

If you look at an Iges file, there is absolutely no difference between an enclosed surface and a solid. The only difference is how the modeling software handles the data when adding new features. You could make an enclosed surface in "surface only" software, export to Iges, pull it up in SolidWorks, and it would be a solid .

Surfaces have normals just like solids. On solids, the normals are all pointing the same way. The same condition can exist on an enclosed surface. The only difference is how the modeling software handles it.

Extrudes and cuts are just trimming and knitting the new geometry into the existing body. Even fillets are just creating a new face, trimming the surrounding faces to make it fit, and then knitting it all back together.

The way I think of it is that surfaces and solids are the same thing, but solids follow a set of rules which make them act more "intelligently". Sometimes you can use the intelligence to your benefit, and sometimes it's too much overhead. That's why solid modeling usually saves time as compared to surface modeling, but when you need extra control or the automated "intelligence" gets in the way, then surface modeling offers the face-by-face/trim/knit functions you may need.

matt

Reply to
matt

created a dodecahedron using surfaces planes and mirrors and one knit. 20 min

Corey

Reply to
Corey Scheich

Interesting thread and discussion. I like to think of solid model's definition as: Solid models are a means to an end to actualize a physical model, therefore it (solids) needs to understand volume. There is another world that runs parallel to our mechanical engineering one and that is the graphic post-production industry. They is not concerned about this goal (physical model) but rather their means to an end is a graphic representation only. Because this is their goal, they but aside NURBS, CSG (constructive Solid geometry) techniques in favor of Polygon mesh representation which is faster and more economic (need not be burden with addition information like manifold and non-manifold volumetric data). We also have a form of this polygonal mesh in order to render OpenGL and PhotoWorks data called a tessellated or faceted model, but that is hidden from the SWX user. I wish the there was not a divide between these two worlds because both have something valuable to offer the other. We need better rendering and animation techniques that MAX, Maya and Lightwave have in our Solids world and they could use the ease-of-use and straight-forward metaphor of Solids modeling to build in their world.

Reply to
Mark Biasotti

Do you mind posting that dodecahedron.

I tried (again) a tetrahedron in the 3D sketcher. By definition all the points of a regular polygon lie on a sphere and all the edges are equal. So I should be able to create a series of equilateral triangles assembled into a bigger equilateral triangle and then put coincident relation between the vertices and a sphere. First of all, I can't put equal relations on 3D sketch lines and second when I try attaching vertices SW will choke.

I attempted a dodecahedron by creating a pentagonal surface and then mating them edge to edge. After about 5 or six pentagons had been added to the assembly I started getting mate errors. I didn't use mirror to get my figure. Not only did I start to get mate errors, but I started to get could not save document errors (and I wasn't saving the document) when I was in the mate manager.

Reply to
P.

I think Bertollini's definition of a solid has to do with multi-dimensional constructs that have specific mathematical properties in a sense similar to those that triangles, rectangles, pentagons, etc. have in a plane. For example, he classifies a hyperpolic parabaloid as a surface even though it takes up 3D space, but a tetrahedron, right prism or right pyramid are solids in that there are special relationships between faces, edges and vertices.

Like you say, some people think there is something inside a solid made by a

3D modeler, but of course there isn't. The 2005 "Select Other" method makes this obvious. 3D modelers just enclose a volume because that is relatively easy to do.

My concern at the moment is modeling regular solids of the tetrahedron, dodecahedron flavor as parametric parts. Right now it seems the 3D sketcher is not up to it because of the limited set of relations available. Assemblies run into other problems and limitations.

The use of the word solid as you have stated can get >> ... heart of the question: "What is a solid?". ...

Reply to
P.

I was able to make a tetrahedron in 18 minutes. One 3D sketch. No surfaces, no knitting.

I made a dodecahedron by assembling some extruded pentagons. Then I made a incontext part from that assembly. No surfaces, no knitting. I had to use vertices zero distance mates and some of the pentagons show in the assembly that they are not fully defined but in all reality they are and can't be moved. They all have 3 vertices mates per part. When I measure the resultant edge line lengths and angles from each face they are all equal to 8 decimal places. I also ran the part in cosmos express just fine.

If you want to see the parts send me your e-mail address.

Dan at bovinich d o t n e t

Reply to
Dan Bovinich

This stuff is way over my head (I'm severely mathematically challenged and not very swift at geometric conceptualization, either), so this is just for fun, airing thoughts, I learn from voicing dumb suppositions and being set straight ...

Takes up 3D space (is non-planar, requires a "bounding box" to enclose it), but it doesn't define a volume? (Or can it?)

Tets are mult-surface groups that do define a volume? (Tet meshes for FEA just satisfy the need for an orderly internal node distribution, connect the dots for stiffness matrix?)

I think it might just be that surface topology is all that's required to satisfy the requirements, for most purposes, where a "solid" description is required?

Interesting. What's the application (if you're free to say)? Do any of the "Golden" concepts (rectangle, ratio, ... ) apply or help with the layout? Is using "3D" tools the best way to go or would setting up planar relationships be more appropriate (dunno, not familiar with SW and don't really grasp the concepts)?

Yes, there are aspects that require assumptions, "fudge factors". Where they won't work they must be treated as assemblies, specialized entities (laminate elements), etc., but that all goes beyond the topology considerations.

Reply to
Jeff Howard

I created a surface and assembeled it as you did but I only assembled it to figure out the angle between faces. Once I had this angle I started mirroring over planes that were defined by selecting the surface and one of it's edges and using the angle I found in the assembly. Once I had all the sides put in I knit the volume and there you have it a solid.

Reply to
Corey Scheich

Just because it is more difficult to create certain 3D (solid) shapes in SWX doesn't mean it is not a solid modeler. As others have shown here, it is possible to create these solid shapes in SWX; it just requires some creative contruction methods.

SWX really is a 3D solid modeler, but its interface and modeling style just doesn't lend itself to certain types of shapes as well as others.

Reply to
Arlin

I tried to assembly all the surfaces which would be a prerequisite to making a parametric model. If you try this, you may find SW starts to choke or get confused on mates. Ideally one could mate the vertices to the surface of a sphere much like an circumscribed pentagon's vertices mate to a circle. Then the circumscribing sphere diameter could be the parameter (or inscribing).

It would be tedious to have to do all these intermediate steps especially when triangles, pentagons and hexagons might be combined to make the solid (of course then it wouldn't be a regular solid).

Reply to
P

I agree Arlin. In the real world, where companies like SolidWorks have to make money, why would they make it easy to model these polygons? Survey SW users and ask them how often they have a need for modeling these shapes (probably .0001% of users.) I never before made those shapes and in just a little time I was able to do it (see my previous post.) I'll bet you if SW had a need for making these weird solids that they would make a module (like their sheetmetal or mold modules) that would make every one of them in a few mouse clicks.

Dan

Reply to
Dan Bovinich

I miss these newsgroup modeling challenges.

I got the basic dodecahedron as a single part in 4 minutes, with four features (two extrudes and a couple of delete faces). But, of course, it wasn't initally precise because I didn't know the angle for the sides.

I eventally (20 minutes) worked out how to get a layout sketch to give me the angles and depths - being lazy, I did it with a couple of lofts whose sections and planes were driven by the layout sketch because I didn't want to mess with equations, plus the same delete faces. It would only take a minute or two now to get the layout to drive the simpler tree. But as it stands, it is a beatifully parametric (and stable!) dodecahedron, and you can define it however you want - by the length of an edge, the circle inscribed or circumscribed around a face, or the sphere it must sit inside or circumscribe.

Anyone beat four features plus an equation? ( I'm counting the equation driven version that I didn't get around to finishing - two extrudes, two delete faces, and one sketch that carries all the magic + a derived version of that sketch)

-Ed

Reply to
Edward T Eaton

The reality is that SolidWorks is just a shortcut for making individual faces then knitting them together into a solid. Up unitl know they have focused on useful shapes (cylinders, cubes, etc) that pop up in real world products. If they could recapture the investment, they could pretty easily make code for more involved shapes (my proof of this point - remember how they added n-sided polygons into the sketcher a while back? Ever use display/delete relations to see that process they used to make those n-sided polygons was essentially what regular folks used to do manually when they needed to make n-sided ploygon sketches before the feature was added?)

Cubes are a pain in the ass to model if you have to model each face individually, but cubes are useful so a coder at SolidWorks made a shortcut for us. If fashion shifts and dodecahedrons, tetrahedrons, and other dungeons and dragon dice shapes become essential to industry, Solidworks (or a third party vendor) will automate that junk in a jiff. But as long as the ancient greeks remain ancient, a lot of these 'poetic' shapes will stay from being a button press away.

-Ed

Reply to
Edward T Eaton

Dan,

Sometimes I get a bit philosophical about things which has its place. Asking a question like why would SW make it easy to model regular solids is a very good question. It doesn't really have to do with marketing, more with capability. The capabilities needed in the software to make regular solids may be more important than you think. Everyone who has made these shapes here has not been able to make them parametric in the sense that polygons are parametric in the sketcher. These kinds of abilities extend past regular solids and into real world problems that are contstrained in 3D space instead of 2D space. If you try to make a tetrahedron by making the vertices coincident to a circumscribing sphere it can possibly be done, but you cannot make the edges equal by relationship. If you try to make a tetrahedron or dodecahedron by mating faces in an assembly you will get into trouble with overconstrained mates (and in my case causing SW to CTDT). Hmmm. And there is a difference between making something that looks like a dodecahedron and something that is a dodecahedron (i.e., carries with it the parametric/mathematical properties of a regular solid). So for example, are you saying that only .0001% of users could use an equal relation in the 3D sketcher or the ability to make features in sketches and sketch plane definitions simultaneously related?

As far as reap> I agree Arlin. In the real world, where companies like SolidWorks have to

Reply to
P.

This is fun...

One layout sketch, two extrudes (one cut), two equations (Why can't I drive a linked value with an equation? Why can't I link to a driven dimension?) I'm pretty sure I could adjust the layout sketch to be driven by edge length, diameters, face width, whatever.

Reply to
Dale Dunn

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