Parametric vs Direct Modeling: Which is better?

When someone talks about CAD (Computer Aided Design), they can mean different things even with the same word. There are significant differences between CAD programs, the tools they use, and how they approach generating three-dimensional models.

The two most common paradigms in CAD are:

• Parametric modeling
• Direct modeling

These two 3D modeling approaches offer different benefits and drawbacks.

What is the difference?

In both cases, models are created by using sketches from which bodies are generated using modeling functions. The key difference is how this creation happens and to what extent the result can be adjusted later.

Parametric modeling

In parametric modeling, computer models are created by drawing curves in 2D sketches and building surfaces from them using modeling commands by specifying parameters to capture modeling features.

Basically, you create mathematical relationships (called modeling features) between the sketches (2D drawings) and the final body. These relationships are built on each other over time so they get connected. It means that modifying something (like changing the length of a line or a curve) that was created many steps earlier, can have an influence on another relationship that was created much later. This connectedness has many benefits and drawbacks as well.

To adjust a design you have to modify the parameters of the modeling feature you created (like changing the length/angle etc) and the changes will happen automatically to the model.

If you change a few values, you can update the model instantly. It’s also possible to adjust multiple areas of a model at the same time with a few changes. This is why parametric modeling is very popular amongst engineers during the manufacturing process.

However, take a very complex model that was created by hundreds of modeling features (relationships). If you want to modify such a design, you need a deep understanding of how it was built, so you don’t break it when you change a parameter. The geometrical relationships can get extremely complex, and if you don’t understand the build logic behind the model, you can easily break the model.

But it can easily happen with not so complex models too if the relationships contradict each other.

That’s why it takes years of practice to master parametric modeling. With all its advantages, the complexity and time to learn are serious obstacles for many people to successfully use any parametric modeling software.

In contrast, direct modeling offers different benefits.

Direct modeling

In direct modeling, computer models are created by drawing curves in sketches and building bodies from them using modeling commands.

• The difference to parametric modeling is that no modeling features are captured in direct modeling. It means that no complex geometrical relationships are created.
• This is a huge advantage, as you are able to adjust the model wherever and whenever you want to, as there are no connected relationships to break.

To adjust the design you can directly manipulate the model. No need to update the sketches or the relationships.

You are able to quickly adjust the design geometry. It makes direct modeling a very effective process when you want to explore ideas and design variations.

This is why direct modeling is very popular with designers during the creative phase of a project.

Direct modeling with solid models even allows removing geometrical details which were added in previous steps.

An additional benefit is that with direct modeling you can easily adjust models that were created with parametric modeling. Just import the cad model into Shapr3D and start directly manipulating it.

In a direct modeling environment, you don’t need to know the complex feature relationships that was used to created the imported model because during the export process every CAD application removes the captured parametric data and saves only the raw geometry into a file format of your choice such as STEP or IGES which can be imported into Shapr3D.

Where can Shapr3D be used and for what?

As a direct modeler Shapr3d can be used in a range of areas such as industrial design, architecture, toy design, furniture design and more where the designer wants to use direct modeling strategies starting with quickly exploring concept ideas and ending with refining the manufacturing model.

It is also possible to export design from Shapr3D to be imported into other CAD application where with a parametric workflow the design will be rebuild if needed or further adjustments are added.

Integrating parametric and direct modeling

It is possible to:

1. Do parametric modeling first
2. Import the final output to a direct modeling tool and
3. Continue working with direct modeling

However, it's not possible to do direct modeling first, import the model to a parametric modeler and continue modeling there.

When somebody else creates a parametric model, first they need to learn how it was built to be able to adjust it. That is the main reason why the parametric workflow is so complicated.

Both direct modeling and parametric modeling can lead to the same CAD result and can both be used to create concept models for ideation or a final prototype model for manufacturing. Direct modeling is just easier to learn, and have many advantages over parametric modeling in terms of workflow integration.

The workflow

Shapr3D fits nicely into a designer’s workflow, because:

• You can create models directly in Shapr3D and modify them later
• You can import models that were created with a direct modeling tool and modify them
• You can import models from a parametric modeling tool and modify them

So, Shapr3D is very useful in a meeting room with clients, because you can directly edit or showcase models. It’s also handy in general for exploring ideas fast with using the Direct Modeling workflow. When a final design is identified, you can export it to a different CAD app to rebuild the design if needed.

You can use Shapr3D for rapidly creating concept models, manufacturing models and explore ideas fast where traditional parametric models are very slow and complicated.