# Surface vs. solid modeler: the differences ?

Hi all,

I tried searching high and low for older posts regarding this question, but I don’t think I found anything so I apologize if this has been asked before. I just took Alias last semester and now I found out that we also offer Solidworks too at school, so I want to take that as well eventually. The professor once tried explaining to the class the difference between them (wasn’t too successful) and I have since learned on here the words “surface” and “solid” modeler, but I was wondering if anyone could explain the difference between the softwares in common layman’s terms?

Thanks!

The short easy answer is that with solid modeling, forms are built-up by drawing outlines and protruding them into forms, as well as using other protruded outlines to cut forms. Often these shapes are more geometric overall, and solid modeling is usually used to create the internal details of products. SolidWorks is a solid modeler (but can create surface forms too)

Surface modeling develops shapes by stretching a “surface” between 3d curves that you individually create. With it you build forms by creating one small surface at a time, slowly creating the complete shape. The intersections between the surfaces are very controlled so they can be very very smooth or crisp like a crease. Usually the shapes are more freeform and sleeker than an object that was created with solid modeling, but some people are very good and the lines blurrr… Alias is a surface modeler, but Solidworks can create shapes with surfaces too

there are some other differences like parametric history and assemblies as well that make Solidworks a worthwhile software to complement your Alias skills…

The math in both is the same. Here is the progression of CAD.
2D CAD>3D wireframes> Surface modelers to show changes in curvature within the 3D wireframes>Solid modelers to automate a lot of the manual surfacing techniques.

Essentially solid modelers and surfacers are offshoots of the same nurbs technology. Solid modelers were developed for engineers, while A-class surfacers were developed to create intricate surfaces.

This means that solid modellers are typically built with more robust engineering tools, while surface modelers are built with more of an emphasis on creating aesthetic external surfaces typically for automobiles, then trickling to mainstream products.

The lines really are blurred. Rhino has solid modelling capabilities while proE has superb class A surface capabilities. It comes down to how you think. Though they are very similar under the hood, surface and solid modelers are configured to two different psychologies- engineering and styling.

I always explain this type of question by first telling users that there are three types of modelers out there.

1. Surface modeler. NURBS and BSPLINE;, Solid modeler like solidworks and Pro/E are subsets of the surface modeler family but very specific sub sets. Parametric - solids .

2 Polygon modeler -

3 Sub’d modeler - T-splines i suppose would fall under this category. Maya does all three, NURBS, Polygon and Sub’d.

Now that is out of the way let me emphasis that alias has specific continuity and control over a curve which drives surfaces that Pro/E and Soldiworks will lack. Those parametric tools are stuck in the 3rd degree … that is y=x^3 type spline geometry from your Algebra equations from high school. Alias Auto Studio can generate curves up to the 7th degree i.e. y=x^7 without isoparms or knots as it is referred to in software programming for CAD.

As far as proving form in one tool over another. Pro/E and soldiworks with work around can do non-proportional scale like Alias or Rhino, and offer a more solid package for a designer. (pun not intended)

Search Google for: NURBS, Sub’D, and A-Class Surfacing.

That is why Alias is used to mock-up design auto and auto interiors … a designer gets more control over the curve. I spent 15 years trying to understand exactly what that means BTW. Which is why when I teach a G2 workshop in Pro/E part of the class is spent showing alias studio tools and what more control actually means with examples.

Now… which is better for you? I would suggest the solid modeler first because that would be the easiest way to get employment… then later specialize in the other. I always suggest to our students to get the basics then specialize in order to differentiate from others that don’t take the luxury too take classes. Also engineers often control the budget so I suggest learning the tool that the engineering team uses then later learn the sexier surfacing tools.

man Design-engine, you might have gone a little over layman’s terms with that one

Its a recession… Im board.

Thanks guys for taking time out to write about this subject and clarifying the differences. I highly appreciate all your knowledge. One thing I have noticed, when I look under job requirements for ID jobs on Coroflot, it seems most of them ask for Solidworks experience, so I plan on definitely learning the program for sure before I graduate. Alias, I can practice some more at my own pace.

Thats the smart thing to do- check and see what the market is asking for. Design-engine is right. Solid modeling is bread and butter. Surface modeling can be more specialized.

I think Travisimo’s got it right for the layman. I describe it similarly:

Solids modeler: Starts with a solid object. You add and subtract other solid objects to it. If you cut into it, you’re left with your solid object minus what was cut out–just like in the real-world. It’s all very rational.

Many solids modelers are “parametric” meaning you can go back and look at the list of commands you’ve executed since the start of your model (the “construction tree”) and change anything (hoping your model doesn’t “break.”) Very useful!

Pro/E and Solidworks are the most popular.

Surface modeler: A bunch of infinitely-thin membranes defined by boundary curves. If you want, you can connect one membrane to another, creating a “water-tight” form that looks solid, but if you cut into it, it would be hollow and you’d have to patch the missing cutout piece (intersect tools are typically used to automate this.)

Surface modelers generally aren’t parametric. There is no construction tree. It’s very hard to change something you did and expect the rest of your model to update.

Why would you use a surface modeler then? Because it’s more freeform, and historically, the tools have allowed you more control over the shapes of those “membranes” than if you were using a solids modeler. And because designers have been attracted to this, the user-interfaces tend to emphasize the freeform more than the solids-modelers, which cater to engineers.

Alias and Rhino are the most popular.

what about exploration or getting exactly what you want in solids? do you guys find that you can explore form, transitions and graphics while working in solids?

working along side solid modelers in the past I found that they always would produce something that was close, but not always what they/I wanted. there would be a jacked up blend here and there or all the spacing was rounded to convenient numbers and often emotionless.

I got a bad vibe for using a solid modeling package to finesse and discover the subtleties of a product. no way to cheat something to see what it would look like really fast. I like the fact that im forced to create each patch and shape in a surfacing package. I like seeing and feeling(rp) several variations as I go. not sure, maybe im just a control freak.

I choose Alias over Rhino because of this discovering aspect. I can move curves, surfaces, CVs and watch the shape come alive and see the difference. To me, Rhino and solid packages for that matter, are awesome to get 1 thing done, but lack the ability really drive variations and chooses which for me is the fun part of design.

ciao gotta go surfin’

um… have u heard of grasshopper or scripting?..

True. Grasshopper is super cool. have not seen it in the ID process yet.

maybe not specifically ID, but deff in the concept phase for arch. do some googling or PM me for specific sites.

In a program like Pro/E you can use both methods on the same model for some really cool results. I often use surfaces to slice away areas of a solid. Or I’ll start with surfaces, turn it into a solid and poke holes in it or whatever I need to do. Also, the surfaces in Pro/E are very parametric. You can tweak them to an insane degree if you build them right. Ask Design Engine for a demo on that one.

I keep refering to Pro/E because I don’t know Solidworks. Alias has some really cool features but there aren’t nearly the amount of jobs as there are for Pro/E and Solidworks. More companies use those. Hell if you have time and money learn all of em!

OMG You’re a 3D software teaching guru and you needed 15 years to fully master the intricaties of 3rd level or 7th level surfaces ?
I doesn’t make me feel I’m close to knowing everything about surfaces !

PS : Would like to live in the US to follow your courses !

Why not the best of both worlds?

Solidworks has been working very hard to improve their “surface” modeling since the 2001 revision. The current revision has very good surface construction AND you get to use solids in the same part/assembly. Hard to beat that. Designers AND engineers using the same program?? Get out of town!

Oh, and it is dimension based!