Thursday, August 13, 2009

Editing 3D Geometry (Introduction)

While history-based systems are learning how to interact directly with geometry and are becoming more “explicit”, history-free systems are learning how to drive geometry indirectly, or “parametrically”.

So what’s involved with editing 3D geometry? When we use a 3D CAD tool for design purposes we are basically describing and transforming 3D geometry in a virtual environment. Today this process is done “directly” or “indirectly”. Indirect describes the typical methods where structure and intelligence is defined and later modified to drive 3D geometry. Direct describes the “explicit” methods of interacting directly with 3D geometry. Interestingly enough, today both of these interaction models exist whether the 3D CAD system is history-based or history-free.

This article turned out a bit long so I’m going to break it up into a few parts. With these posts I want to specifically review the details of how 3D geometry is edited and modified in a 3D CAD system. I think that as we CAD users learn more about what is going on in our CAD systems and why, it can make us better users. I hope this discussion will help.

In the next two posts I will discuss these two technologies in detail. We will first take a look at how “indirect” editing works in the history-based environment and how it works in the history-free environment. Then we will take a look at how “direct” editing works in each of these two environments.

Watch for the following two posts in the near future. You can click on the follow-me link on the right side to be informed when they are posted.

Editing 3D Geometry – Indirect

With indirect editing, parameters, dimensions and other intelligence is added to the model that will define possible transformations and relationships. In a history-based system this intelligence is captured in the history-tree at the time the model is being created. With a history-free system the intelligence is captured in the B-Rep model during or after model creation. In either case this intelligence can be used for maintaining geometric relationships and for specifying geometry transformations.

  • Indirect Editing; History-Based
  • Indirect Editing; History-Free

Editing 3D Geometry – Direct

Direct editing requires no intelligence to be assigned or managed. This technology provides the ability to interact directly with the 3D B-Rep geometry. Directly manipulating a B-Rep model is not trivial but we are getting much smarter at it. As the edit is being done directly, geometry must be selected to edit and transformations must be explicitly defined.

  • Direct Editing; History-Based
  • Direct Editing; History-Free

At the end of these posts I will provide a quick summary and review of how these technologies can impact your product development process. Hopefully you will have a better idea of where these technologies can provide value.


Part 2 = Editing 3D Geometry - Indirect Editing

Part 3 = Editing 3D Geometry - Direct Editing

Part 4 = Editing 3D Geometry - Summary

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