Even experienced CAD users may be uncertain about just what direct modeling means for the operator. With this blog post we want to focus more specifically on the hands-on differences to a user that direct modeling CAD can make. (We have a webpage dedicated to "What is Direct Modeling?" that describes the principles in a more general way.) So, to help explain that perspective on the differences between direct and parametric systems in more detail, here is a list of seven reasons a user can benefit from direct modeling.
1. No history/feature tree
The difference that users notice right away is that direct modeling doesn't rely on feature-trees to build a model. If you're used to parametric modelers like SolidWorks, you know model geometry is continuously rebuilt from the top operation in the tree to the bottom — the history. With large models this method creates complex dependancies that sometimes cause trouble, particularly over time. You may be familiar with elements of the interface such as rebuild errors and red Xs populating your tree: the model which was working great a few years ago “stops working.”. Direct modeling doesn’t have those features. A direct model is the final geometry, not a recipe to create geometry.
2. Simple changes are still simple
A CAD user getting familiar with direct modeling often wonders right away: "How do you make changes if you don't have a feature-tree?" For a simple example, to edit the size of a through hole in a block using a parametric modeler, the user typically selects the hole item in the feature tree and edits the diameter value. The system rebuilds the model with the new parameter value and the user sees the resulting change — simple. In direct modeling the user would typically select the cylindrical face of the hole, run an edit command, and type a new diameter value. The system offsets the cylindrical face, retrims the surrounding faces, and the user sees the resulting change — simple. Both modeling approaches also allow for a diameter dimension on the hole to be used to drive that simple change quickly and intuitively.
3. Never start over from scratch
The primary purpose for parametric modeling is to construct models that can be reliably and quickly edited, even in sometimes complex ways, within a specific set of parameters/conditions. Its primary weakness is what happens when the foundational set of conditions change outside the boundaries the model was designed to handle. The answer is that it is often more productive to start the model over from scratch — commonly days of work! With the direct method, the model is never locked to assumptions made at the start. Even if some of the geometry needs to be torn apart to make radical changes, the new parts can then be merged back into the rest of the model.
4. Design freedom
Without needing to worry about the future impact of each move, direct modeling users can experiment quickly without getting boxed in. It is simple to create alternative portions of a model and organize them with layers, like in 2D CAD. Direct Modeling can also be as simple as cut and paste. If you want to remove an entire piece of the model and place it elsewhere, copy the feature or set of features and with a few simple moves, place it where you want it. No digging around in a feature tree to recreate the steps. If you are always asking yourself "How am I going to make this one little change without messing up the rest of the model's history?" it will be worth your time to try a pure direct modeling CAD. With direct modeling, you can access the geometry you need without affecting other elements of the model.
5. Direct access to all models
With direct modeling, if there is geometry in the CAD file, you can work with it. Regardless of whether you created the geometry or received it from someone else — regardless of what platform they use — you can always make changes or quickly build new parts based on the imported content. Simply put, direct modeling can be used like digital 3D sculpting tools: whether you changed your mind on your work, or a revision was called for from elsewhere in the process, direct modeling allows you to alter exactly the geometry you need to, regardless how it was originally constructed. The feature trees of parametric modeling systems are very difficult to translate between different systems, and often they don’t transfer at all. In that case, modern parametric systems typically fall back on an incomplete set of direct features that can make some simple changes. Users often need to start the model over from scratch in order to get control of serious edits to “foreign” models.
6. Direct Modeling = Full Featured CAD
CAD users who are familiar with direct modeling as a limited feature-set within a parametric platform may be surprised that a full-fledged, complete pro-level CAD can work exclusively through direct modeling. There are several decades-proven, full-featured CAD software platforms that meet the needs of contemporary users across all manufacturing sectors. (Ours is KeyCreator, if you didn't know.)
7. It's intuitive to learn
Direct modeling is an easy transition for someone who is already familiar with 3D CAD. For people who already know how to program a parametric system, you'll probably be up and running within a couple working days, depending on your skill level. For 2D CAD users, direct modeling is much more intuitive to learn than trying to master the concepts of feature history dependencies needed in parametric modeling. Finding the instances where direct modeling can be more efficient as a user will become especially clear to those who need to make modifications to files from outside sources, or those who frequently develop all-new designs.
Not every CAD user is working in an environment where direct modeling provides an obvious, distinct advantage. But if the differences we've cited here sound familiar to you, it's worth your time to consider how direct modeling might be a valuable tool to include in your process.
NOTE: This blog post was updated in January 2024 to reflect ongoing developments in the CAD marketplace since its original publish date in 2014.
