Direct editing is being introduced into history-based CAD systems now to simply provide another option in history-based modeling for the editing of 3D models. With good direct editing we can be somewhat less dependent on a well-structured feature tree. However it does seem that some parametric history-based purists consider direct editing within a history-based CAD tool as somewhat of a risk. Perhaps they are concerned that it provides a way to “corrupt” the design intent. I find this a little strange in that if in fact the design intent (feature structure and definition) is already pure and perfect, there would certainly be no need for direct editing. Unfortunately this is rarely the case.
In reality direct editing in a history-based tool is just another parametric modeling feature. And like any parametric modeling feature, there needs to be clear best-practices and modeling standards associated with it. If used correctly, direct editing can be one of the most powerful parametric modeling features you may have in your CAD toolbox.
I want to try to highlight some of the potential power of direct editing within a history-based model in the video below. In this case I will be using Creo Parametric. PTC added direct editing to Creo Parametric with what they call “Flex Modeling”. Mature direct editing requires tools for geometry selection, methods to define the transformation (edit), and robust predictable results.
So having another method; direct editing, for creating an intelligent and ordered parametric feature can be very powerful when used correctly. It should be nothing to fear, but rather leverage when and where it makes sense – as with any parametric modeling feature.
PTC has done a nice job integrating the necessary functionality with a robust kernel to make their direct editing (Flex Modeling) very capable, predictable and robust. The same can be said of Siemens and their direct editing (Synchronous Technology) in both NX and Solid Edge. But as you consider direct editing, pay close attention to these three things:
- There must be good geometry selection methods including feature recognition, geometry rules and the ability to add and remove from the selection
- There must be intuitive methods for defining the transformation including dynamic handles and dimensions. AND, you should be able to make multiple transformations in one edit.
- You must get stable, predictable and robust results. In some cases there may be multiple results to a given transformation. The system should provide the possibilities and allow the user to select the appropriate one.