Direct Modeling Use Vs. Parametric Aerospace or Any Product Design

Hi Guys, I am an aerospace engineering junior year student. Our school teaches us NX and Catia which I believe are mostly used software in the CAD world for aerospace and automotive engineering.

So, personally, I loved Shapr3D because it is on iPad which is portable and uses a pencil, and is easy to use. My professor says direct modeling is not used because it doesn’t provide the accuracy necessary for the strict design. Now, I am confused in what way can shapr3D be useful for me as an Aerospace engineer? Also, what is the aspiration behind the shapr3D development if direct modeling is not useful to make a strict and accurate design? I still love the shapr3D, but I am not sure if this will be useful for me in the long run. I need some expertise guidelines without any biased answer.

Hi @Krish

This is simply not true. Although direct modeling is indeed less popular than history based modeling, but this is due to two reasons:

  1. Modern direct modeling is just 10 years old while history based modeling is almost 40 years old
  2. Because of this there are very few proper dm cad systems on the market, but actually nowadays every CAD system provides direct modeling functionality, including NX, CATIA, Solidworks, etc. These direct modeling features are used in aerospace too, eg. offsetting a face is a direct modeling operation too.

The confusion might come down to a misunderstanding of the term direct modeling, where many people associate dm with push pull interactions, but these are two different things. A history based modeler can also use push pull interactions, it’s just a more intuitive way of setting the parameters of a modeling operation, instead of entering numbers.
In terms of accuracy, direct modeling is exactly as accurate as history based modeling. If you do the same operations in NX, or Solidworks or Shapr3D, the resulting geometry will be the exact same geometry, with the same accuracy, simply because all of these tools are running on the same geometry engine: Parasolid.
Actually even NASA is using direct modeling tools, and although direct modeling and history based modeling are a bit different, the difference is not the accuracy of the models they create, the only major difference between the two is how they let you modify geometry. History based modelers will let you edit the history (modeling steps) of your design, and “replay” the later steps, while dm works directly with the 3d geometry and lets you directly manipulate features, faces and edges.

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Thank you so much for the reply. So if that’s the case can you please elaborate on detail on what way direct modeling is better than parametric modeling and why still designers in engineering prefer parametric modeling over direct modeling ?

Sure, we have an entire article about it: What's the difference between parametric and direct modeling? – Shapr3D Help Desk

Basically the advantages of direct modeling are:

  1. faster, no feature regeneration, etc.
  2. there is no “design intent” in the model, so it’s easier to respond to unforeseen changes in the design
  3. easier to modify imported models: history based tools without direct modeling have limited options to modify imported geometry, while direct modeling works exactly the same for imported geometry. You can easily move a hole for example, or offset a face using DM operations.
  4. no feature dependencies: in history based tools, by design you need to create dependencies between features. This very often leads to a broken feature history, that often needs to a complete remodeling of a part or even an assembly. In direct modeling this does not happen, because of the lack of these dependencies. This is particulary problematic when you are working with a part that was designed by someone else. This is actually considered to be so risky, that often CAD designers rather redesign a part from scratch instead of modifying someone else’s design history, because it’s can be so hard to figure out how and why the feature tree was designed in a certain way.
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Furthermore to Istvan’s comments. I can hand my iPad to my wife, a friend, a child, and tell them to draw a circle, then make it a cylinder. The intuitive nature of Shapr3D, allows them to create these objects easily. I’m on the BoD of the Discovery Cube in Santa Ana, Ca. We have young children there learning about STEM. We use iPads and Shapr3D for them to learn, because direct modeling is far more intuitive. We use to use TinkerCad there. But even it’s methodology is inferior to the direct modeling of Shapr3D. It’s a bit of old school thinking vs new school thinking. I’ve been using 3D modeling since 1979 with ComputerVision in Aerospace. I’ll take Shapr3D any day.

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What he said, modeling since 1983… It’s also more fun.

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Many times when using Fusion 360 in history mode I’ve made changes to early operations that complete broke the history timeline. You really have to carefully plan when using historical modeling whereas direct modeling doesn’t care when in the process you created a feature: you can tweak it to your heart’s desire in-place.

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I appreciate for making me clear about the concept of direct modeling and parametric modeling. I think you guys are doing great with examples videos and webinars related to mechanical engineering and crafting work. But what I believe is if you want to diversify the use of Shapr 3D in other fields like vehicle design, Plane design and much more you should bring more concrete examples of the design approach for those kind of advance design. I have seen some examples of water pump design and I have learned a lot from it. But what I want is to learn more about the approach for design process for advance vehicles, since this product is new some real good examples related to diverse field will attract students like us who are eventually the engineers and leaders of upcoming decades.

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Something @Istvan_CEO_Shapr3D mentioned when I asked a similar question is that Direct Modelling does not appear to allow you to alter aspects of a design that were created early on without completely messing up the model. If that is true that would be a pretty big impediment.

As an example, let’s say you’ve got a gear model, and you want to change the gear pitch or diameter. I don’t know of a way to achieve this in DM.

I am VERY happy to be proven wrong.

That’s a two-sided coin. There’s no guarantee that changes you made since creating the object won’t interfere with parametric resizing. I’ve run into that several times in Fusion 360 and ended up having to fix a bunch of interim steps every time I resized.

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