3D modelling vs CAD


  • Anonymous


    I am a complete amateur. I know what I want to draw, but I don't know whether I need a 3D modeler like AoI or a CAD program like FreeCAD. Honestly, I don't truly understand the difference between these two types of programs: I know that "artists use 3D modelers, engineers use CAD", but that doesn't tell me enough.

    Anyway. I am an astrophysicist. I want to draw a model of a space colony idea that I have been working on.

    1. On the one hand, I don't just want to draw a pretty picture. I have been thinking seriously about a design that is as realistic and as plausible as I can make it. I have notes regarding safety design, evacuation procedures, temperature control, natural lighting, etc. This makes me think that maybe I need a CAD program because… you know, "that's what architects and engineers use".

    2. On the other hand, I am not an architect or engineer. Though the colony is meant to be more realistic than most well known designs, its construction still lies well in the future (late 21st to 22nd century). I have no intention or ability to design every detail like plumbing, exact choice of materials, circuits, etc. This makes me think that a CAD is *not* what I want… Maybe I really do just want to draw a picture.

    In addition, I have no intention of becoming an artist or architect. My day job is to do astrophysics and this is just a fun project that I'm working on on the side. I would prefer a program with a relatively easy learning curve (e.g. I'd pick AoI over Blender).

    Based on this information, can anyone make a recommendation or give me any general advice as to what software I need?


  • Harald G
    Harald G

    I´m working with CAD and don´t know to much about that kind of concept design you´re going to make.

    But as often: You need to plan. And CAD is not a good choice here, because you´re not looking for absolute precision
    (I assume).
    So usually from concept to "art" in this case you need to make sketches.
    You can use a computer here, but usually you might be faster just with a pencil and a sheet (or many sheets) of paper.

    After that AoI is your friend - especially the PME for future design "hard egdes".


  • Peter Eastman
    Peter Eastman

    It sounds like you want an art program, not a CAD program.

    Here's how you can understand the difference.  Suppose you draw a circle.  What if it isn't really a perfect circle?  Is it ok if the radius actually varies by one part in a thousand?  To an artist, that's just fine.  No one will ever notice the difference.  To an engineer, that's totally unacceptable: their circular post needs to rotate freely in its circular hole, and even a 0.1% error will mean it doesn't fit quite right, leading to unwanted friction.

    Art programs and CAD programs look similar, but they're really very different.  Art programs let you create images that look the way you want, and try to make it as quick and easy as possible to get them.  CAD programs are for creating mathematically precise plans that can be sent directly to manufacturing.


  • Bill French
    Bill French

    I agree with Harald -

    Cad would be useful if you had to design all the wiring, plumbing, etc.. But as  you say, all you really need is to show what your concept is all about. That is exactly the point of AOI ;)

    It has a very quick learning curve, and a lot of people both here and on FriendlySkies that will always help out if you get stuck on a way of accomplishing a task. That - you will not find on some CAD forum !!

    With AOI you will discover that you can go from concept to actual 3D buildings in a very short time. Then also keep in mind that you will also have the ability to go on a walk through of your outpost ( inside and outside) !!!!!

    Good Luck -

    ---> Bill

  • Marc

    (Not really a) plug: Check out the new featured images gallery over at friendlyskies.net/aoiforum. If the precision looks good enough to you, I would try Art of Illusion for your project. CAD adds a lot of complexity that can really slow you down if you don't need it.

    You can also make a quick mockup in AoI and keep that version around for testing things like animations or scenery/environment, etc. I know some like to separate interiors and exterior shots into separate files, too, which might be a good idea.

    Also AoI has grid units which aren't tied to any particular measure, but I think we found that they work best at 1 grid unit roughly equaling 1 meter. I say roughly because you don't have to use it that way, but it works pretty well and allows freedom in moving the camera through space, etc. Could be remembering incorrectly; someone correct me if I'm wrong.


  • Anonymous

    Thanks for the help. Those were extremely useful replies.

    Now that I understand better what CAD is for, I know that it's not what I want (Peter's example with the circle and friction was very instructive). As Bill said, I want to show a concept design, so I'll use AOI.

    Thanks again.


    PS: The examples in the image gallery are impressive. I see several mechanical objects like tanks, cars and bicycles. I don't think I'll ever draw something as intricate as those tanks.

  • I'll add my 2c to give (yet) another perspective.

    Instead of asking what the different programs were intended to do, ask yourself what is the output that you want.

    CAD programs produce DXF, DWG, and similar types of files, which represent lines (plans and elevations) or full 3D models, in a way that would enable someone to build what you have drawn.

    3D modelling programs produce JPEG, PNG, MOV (quicktime movie) and similar files which represent what you have drawn in a way that enables someone to see what your model would look like, without necessarily enabling them to build it. In fact, most 3D modelling tools allow you to bend the truth enough that someone could never build what you have drawn - this is part of the fun btw :o)

    So, if you want to model something that you will subsequently build, then a CAD program is (usually) a better choice; and if you want to generate (render) images of what it would look like if it were constructed (possibly with "artistic embellishment"), then a 3D modelling program is (usually) the better choice.

    As in all things, there is a grey area where either, or both, or a hybrid, is/are beneficial.

    There is a DXF importer to AOI, but it is very limited.

    There are renderers for many CAD tools, but they tend to be relatively limited (compared to AOI, Povray, Blender, etc)

    Sketchup sits in the middle - it understands CAD files pretty well, and can draw 3D models quickly and well.
    Overall, the renderers I've seen for Sketchup are still more limited than those in the 3D modelling world - but I've not tried all available renderers for Sketchup.

    Getting back to the output: A number of these tools can also generate STL files (or similar) which would enable you to send your 3D drawing to a 3D printer, so you could create a (usually plastic) physical model of your drawing.

    The renderers for most of these tools will also allow you to create a movie that features your 3D model. The CAD tools usually have limited features for animation that support a "fly-through", but not much else.

    The more artistic tools usually support greater animation options (eg morphing, CGI, etc) which allow far more imaginative movies to be created.

    For example, you would not attempt to create the Shrek movie in a CAD tool, whereas with Blendar or (in theory) AOI you could.

    So, back to my original question: what type or types of output do you want?
    Once you have that decided, then select the tool or tools that best support your desired output.
    Only then worry about the compromises that might be inherent in those selected tools.



  • Anonymous

    Heh… Well, let's put it this way: I'm not planning to send my design to a shop so I can build my own space colony. That said, I've heard that AOI can output to STIL. I know of at least one project (http://reprap.org) that is actively using AOI to design a 3D printer that can print the components needed to make the printer (very cool). They use AOI and apparently export to STIL files somehow.


  • They use AOI and apparently export to STIL files somehow.

    Follow these steps:
    0. Use the Scripts and Plugins Manager (SPManager) to install the STLTranslator plugin (one-off task)
    1. open your scene, and optionally select the obejct(s) you wish to export to STL
    2. Select "File | Export | STL" and follow the prompts.


  • OniOid

    I would also add how much, or at least what kinds of, precision and control you want as you model.
    In CAD programs, there are features that make some kinds of modeling very easy, fast and precise, such as, for example, re-aligning the grid or coordinates to a certain angle relative to the object or element on it and then modeling relative to that.

  • James

    Peter, might I ask if there have been any developments, or more thoughts, over the past few years, since 2007, as to some kind of basic dimensioning in AOI?  Above, where Komatta mentions that "AoI has grid units which aren't tied to any particular measure", is that something that can be displayed?

    And, is there a way to form a template-group of objects, along with some internal "length" value, in explicit "grid units"?

    So, for instance, if there were drawn a thin cylinder with cones on the ends, to represent a line and arrowheads, and perpendicular to this double arrow, another pair of "lines" , cylinders with their axis just crossing at the apex of each "arrowhead" cone, to represent the dimensioning lines, is there some way to automatically display the length of this  double arrowhead "line", this long thin cylinder with cones, in "grid units"?  Or in "scaled grid units", where some arbitrary "scaling factor" multiplies the value of "grid units" to form a displayed value?

    And then, if the length of this "double arrow", and its displayed "length", could be "slaved" or "linked" to the internal dimension of some other displayed object, that would be very convenient.

    I haven't looked at AOI lately - maybe there is already some straight forward way to do these things?