The benefits of 2D parametric design

Written by Guillermo Melantoni

Published Wed 17 Jun 2009

Figure 1 (above),Traditional scenario before the release of AutoCAD 2010. If a user changes the position of the depicted grip the only line that changes is the one which has been selected. Figure 2 (below), After quickly generating a number of constraints on the geometry the same action as above has a quite different result in AutoCAD 2010, providing very powerful editing possibilities for 2D drawings.

People often believe AutoCAD is an application that produces only points, lines and arcs, some even saying that it produces just “dumb” points, lines and arcs.

This thinking no doubt stems from the perception that AutoCAD applies no discipline-specific information attached to the objects, or that the entities inside AutoCAD don’t have any type of persistent relationship that can be maintained after changes.

But the relevancy of the first perception is debatable, since part of the power of AutoCAD relies on the fact that it produces generic content. This enables maximum flexibility for both drafting and design. If users need discipline-specific components and workflows, applications such as Revit or Inventor support those needs. Given that AutoCAD is bundled with these apps, users should hopefully feel they have the best of both worlds: discipline-specific content to enhance productivity, and generic content to enhance flexibility.

Also, with the introduction of AutoCAD 2010, the second perception is no longer accurate thanks to the new Parametric Drawing tools. Both design and documentation workflows can benefit from the associative framework introduced in AutoCAD, that now contains both geometric and dimensional constraints. Parametric Drawing adds intelligence to the drawing, by controlling design intent with two different types of constraints. Geometric constraints ensure that specific relationships between entities (parallel, perpendicular) can be maintained when altering one of the elements. Dimensional constraints allow users to drive the geometry with dimensional values and formulas.

A key benefit of Parametric Drawing is that it allows users to make more changes with fewer edits, ensuring design intent is maintained throughout the revision process. When objects with constraints are amended AutoCAD automatically updates related objects based on rules defined by the user, saving a lot of manual update time (see Figure 1 and Figure 2).

Before diving into the details of the functionality, it’s important to understand the goals that this feature had to meet to be considered successful.

Firstly, establishing relationships had to be optional, with very clear feedback on which objects were affected by these constraints. Parametric Drawing amounts to much more than a single extra feature added to AutoCAD, and it requires a change in the way that users manage their drawings. Therefore, if the application of constraints in entities was not based on the intention to do so, and the results made clear somehow, users could end up with drawings that would not react in predictable ways to changes, or not react at all (due to the fact that they could be fully constrained).

Figure 3: The AutoConstrain tab in the Constraint Settings dialogue allows users to change criteria for generation of constraints. By modifying order and maybe removing some specific results may vary dramatically. This adds quite a lot of power for better control of the drawing

While inferred constraints are a fairly widespread method for applying constraints, AutoCAD 2010 allows users to add constraints actually after making the geometry. This doesn’t result in a loss of productivity. The AutoConstrain feature can be applied to any selection in the drawing, and it will infer constraints according to a set of rules previously defined by the user (found in the AutoConstrain Settings – see Figure 3). This provides for maximum flexibility, since Auto Constrain will react differently according to particular user settings.
As mentioned previously, feedback on the nature and location of the constraints is of paramount importance. The visual language adopted in AutoCAD is very similar to the one available in Inventor, so anyone familiar with that application will find a lot of familiarities. Not only the constraints can be shown on a per selection basis, but AutoCAD also highlights all of the affected entities. This becomes even more important when a colleague needs to work with a file that has constraints. Users can quickly understand what’s happening either with the whole drawing or with the part of the drawing in which they need to work (Figure 4).

Figure 4: When the mouse is over the constraint lables, in this case the collinear constraint is highlighted in the lable, and is also highlighted in the lable at the bottom of this image. The lines affected by the constraints are also highlighted.

Another aspect of the Parametric Drawing feature is that the user can override the constraints at any time by using the Ctrl key. Doing so will relax the constraint. If the user wants to delete the constraint, it’s as easy as right clicking on the label, and removing the selected constraint. The addition of Parametric Drawing to AutoCAD will also help users move to more advanced products such as Autodesk Inventor, Autodesk Architecture, and Revit since AutoCAD users will start to learn a new way of understanding design and even drafting using parametrics. Once the drawing is constrained, the behaviour when making edits to a sketch should be similar in the three applications mentioned (Figure 5).

Figure 5: The Parameters Manager allows the use of formulas and user variables. Whenever the name of any variable is edited the change populates both the drawing and manager.

It’s also important to realise that most of the parametric packages for mechanical design deal with constraints in more controlled environments, for example, the part environments. AutoCAD can deal with a huge amount of constraints, since they are applied in the drawing and not only in the block editor. That’s why a task dialogue warning may appear if users try to AutoConstrain an entire drawing with hundreds and even thousands of entities.

If we now move on to looking at dimensional constraints – these allow the user to apply values and formulas in order to control the design intent. Once a dimensional constraint is added, it can be managed either in canvas by double clicking on the text, or by the Parameters Manager, where users can also add expressions and user variables. User variables may not be applied to any specific entity in the drawing, but can be used in the formulas. These concepts can be traced to apps such as Autodesk Inventor and Revit, making it easier for AutoCAD users to get up to speed on those.

Another interesting feature is that any dimension existing in the drawing can be converted into a dimensional constraint with a single click. This is a great addition to the feature set, since not only can the user AutoConstrain the geometry, but they can also select specific dimensions already applied to become parametric (see Figures 6-8).

Figure 6: From a traditional dimension...

Figure 7: ...Into a dimensional constraint...

Figure 8: ...And adding an expression in two clicks.

Parametric Drawing has also brought some interesting changes to Dynamic Blocks. These blocks were previously managed with actions and parameters. Users now have the ability to add constraints in the block editor environment, and have a much clearer view of the block.

Using an example with an I Beam, this same block before AutoCAD 2010 would have contained a significant number of parameters and actions in order to drive the changes in its design. Now, once the user defines some basic dimensional and geometrical constraints, they can add a link to a spreadsheet that contains all the different values and get the whole job done in a couple of clicks (Figures 9-12).

Therefore, instead of having many different views defined and changing the visibility, users have just one element with different potential sizes managed by a table that can be pasted from a spreadsheet. Not only does the whole experience of visualising a block become much better, but it becomes a smarter way of managing the amount and size of parts.

Autodesk received extensive feedback on the Parametric Drawing tools during the ‘Gator’ (AutoCAD 2010) beta programme, and much of this has been incorporated into the final functionality. Users have reported a dramatic change for AutoCAD, and not only are they finding the application easier to use, they are already noticing significant productivity gains during the design, drafting and revision process.

With simple, flexible tools to apply constraints and predictable results when updating constrained objects, AutoCAD 2010 delivers an intuitive user experience for Parametric Drawing - allowing users to save critical time when revising designs.

Figures 9-10 (Top): Beam inside the block editor. Constraints are clearly represented and the whole block is much more understandable. Figures 11-12 (Bottom): Showing the Block Table and the final result.