Cadalyst - March 2008 - (Page 36)

mcadmodeling History, Nonhistory, or Both? Modeling methodologies offer many choices to meet your needs. By Mike Hudspeth, IDSA hen you import a model from someone else’s CAD system, what do you expect to be able to do with it? Most people want to work with it and incorporate it into whatever they are doing. But depending on what software you are using, your expectations of the actual usefulness of that imported model will change. Why? Because of something called history. No, it’s not about dates and places or somebody in old-fashioned puffed-out pantaloons. It’s about modeling history. If you’re using a history-based modeler, you’ll see imported geometry slightly differently than someone who uses a nonhistory-based modeler. W It’s All History What is history-based modeling? Simply put, it’s the methodology of building your model in a particular order. When built that way, many features in your model will be dependent on those that came before them. Say, for example, you are applying some blends (figure 1). If you have them going around a rounded corner that is too small, they might not fit. The model could self-intersect, and most modeling programs would raise a failure notice. Likewise, if you make changes to your model that violate a relationship, your modeler isn’t likely to allow it. So why use historybased modeling then? Because creating relationships between features in your model also has an upside. You can build intelligence into your model that will be flexible for things such as what-if scenarios. You can organize your models so they make sense and are easy to change (figure 2). Hard-line purists would tell you that you should always use history-based modeling. They see nonhistory-based modeling as a liability. After all, you can’t change it, right? Not necessarily. Figure 1. With a history-based modeler such as SolidWorks, the order in which you add features makes a difference. With a nonhistory-based system, it doesn’t. No History Here I have to admit that using a nonhistory-based modFigure 2. In a history-based modeler such as Solid Edge, you eler is pretty liberatcan group features in organized ways. ing if you’re used to parametric modelers. It can be a lot you’ve created up until now. It hasn’t of work to establish all the relationchanged in years and most likely ships that a history-based modeler won’t in the future. I’ve worked for requires. Sure, history-based modelers companies that have sold the exact have their advantages, but it’s so nice same part for 30 years — and it’s to be able to just do what you want been almost that long since a change to do without regard to what came was necessary. first — the chicken or the blend, er, Sometimes you need parts from egg. When you import geometry into other companies that control their a nonhistory-based modeler, you’re devices. They don’t want you making essentially generating its topology changes to their stuff, so they sup— the general shape of the data, the ply you with what some call explicit, outside envelope. Usually little or no or nonparameterized, data. You know additional information is included. So how it is. I’ve done the same thing, how useful is it? Plenty! and I would guess you have, too. Nonhistory-based geometry has Then there are purchased parts. You many practical considerations. There can download them from all over the is legacy data, which is the stuff Internet — motors, electronic compo- In this article CoCreate www.cocreate.com Kubotek www.kubotek.com Siemens PLM Software www.plm.automation.siemens.com SolidWorks www.solidworks.com 36 March 2008 | cadalyst | www.cadalyst.com http://www.cocreate.com http://www.kubotek.com http://www.plm.automation.siemens.com http://www.solidworks.com http://www.cadalyst.com

Table of Contents Feed for the Digital Edition of Cadalyst - March 2008

Cadalyst - March 2008 Contents Editor's Window CAD Central Thicker than Water Safe Keeping — Backup Software Secures Your Designs AMD’s ATI FireGL Graphics Cards AutoCAD Civil 3D 2008 — Surveying, Civil Engineering, and Land Development Software Cool Software Utilities for Your Job History, Nonhistory, or Both? In the Eye of the Storm Builders’ Information Modeling CAD Cartoon Issue Indexes CAD from the Streets

Cadalyst - March 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.