Christopher Sean Morrison <brlcad@...> writes: > > > Hello Qiang, welcome! > > > I really like the idea of drawing with simple command. But I read a post on > > freeCAD forum comparing the two programs. It says that it is very hard or > > impossible to do the following in BRL-CAD: > > offset on non trivial geometry, fillets and chamfer on non trivial geometry, > > draft angles on non trivial geometry > > You’re undoubtedly familiar with a feature based editing approach, as those are feature operations you > listed. We will eventually add intrinsic support so they are preserved as parametric operations, but > currently they are handled like any other modeling operation. If you want a chamfer, for example, you > subtract. Offsets are a trivial surface and/or object move. > > None of them are impossible but it is true that some of those operations can be a challenge, depending on the > geometry involved. For some (non-trivial) shapes, it can actually be easier to perform an offset or > chamfer operation in BRL-CAD. For others, it can indeed be difficult. The solid modeling construction > methods in BRL-CAD lend themselves more to a different approach in general. > > Basically, our systems come at the problem from separate ends of a spectrum. We focused a LOT on core > solidity concepts — on solid fidelity, ray tracing evaluation performance, correctness, > representation flexibility, numerical robustness, etc., and only recently towards adding boundary > representation support, parametric features, and usability/GUI. This is a foundation that is heavily > centered around a specific domain of computer-aided engineering (CAE) for analysis purposes. > > That means there is almost certainly a way to create and evaluate any shape you want, however complex, but > there is a proficiency learning curve. > > > Are these all true? If so, what should we do to model all these real life > > things that are not composed of simple primitive shapes? > > With incredibly few exceptions, nearly every complex shape can be decomposed into combinations of more > primitive shapes. If you check out our gallery, you’ll see plenty of more complex examples ** that were > composed from simple primitive shapes (including complete vehicles with chamfers, fillets, etc). > Here’s an example model included in BRL-CAD's installation: > > https://www.youtube.com/watch?v=xzaKWzntnmc > > More here: > > http://brlcad.org/gallery/renderings > > Cheers! > Sean > > ** Alas, hundreds of the most detailed examples of BRL-CAD models are not available to the public. > > ------------------------------------------------------------------------------ > Monitor Your Dynamic Infrastructure at Any Scale With Datadog! > Get real-time metrics from all of your servers, apps and tools > in one place. > SourceForge users - Click here to start your Free Trial of Datadog now! > http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >
Thank you Sean. I always find your post very informative. But how can an offsets be a trivial surface and/or object move? If the curve is not straight, an offset will need some shape changes. A dilation of an ellipse is not an ellipse anymore(just to illustrate my point, I could be wrong), then will BRL-CAD automatically generate new primitives to represent the new geometry? I see nurb and spline are still missing, so I guess we can only approximate very irregular surfaces like a computer mouse or tea spoon with polygons patches, it would be disastrous to change all these small patches one by one if I want modifications. In my opinion, command line and keyboard are more attractive than fancy GUI and mouse interactions, it gives us more precise control and less eye strain. Lastly, I find the model share page(http://more.brlcad.org/popular-models) is still broken. Maybe a repository on github is a better place for those files. Qiang ------------------------------------------------------------------------------ Monitor Your Dynamic Infrastructure at Any Scale With Datadog! Get real-time metrics from all of your servers, apps and tools in one place. SourceForge users - Click here to start your Free Trial of Datadog now! http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 _______________________________________________ BRL-CAD Users mailing list brlcad-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-users
