Re: [brlcad-users] Creating an Ogive shape in BRL-CAD
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From: Christopher S. M. <br...@ma...> - 2014-10-14 03:34:48
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On Oct 13, 2014, at 11:08 AM, Cook, Kathy <kat...@lm...> wrote: > I am looking for suggestions on the best way to model a nose cone section that is formed as a tangent ogive (or any other ogive shape for that matter). It entirely depends on the level of accuracy you require. If an approximation is acceptable but you want it be analytically fast to evaluate, you’ll get pretty close to a tangent ogive with an elliptical paraboloid (epa). You could also (fairly easily) generate an approximation with an ARS [1] but you’ll have to manually calculate your surface points (and repeat the process for the interior subtraction). I’ve also seen people use sets of cylinders (rcc or tgc). [1] http://brlcad.org/wiki/BRL-CAD_Primitives#ars If you want an *exact* tangent ogive, the only solution currently available is to model it in another CAD system (e.g., Rhino) and import it (via our step-g or 3dm-g importer) as a NURBS entity. > So, what would be the best way to go about this and get a relatively smooth surface? Our revolve primitive (where you revolve a 2D curve about an axis) is yet *another* way and probably the second best way if an approximation is acceptable. That primitive currently only supports linear line segments (hence, another approximation), but it’s easy to construct. If sketch curves were working, this would also be an exact solution. As for how with sketches, you’d model one curve for the exterior, one for the interior, and create a revolve using that sketch. It’ll automatically result in an empty interior and give you the ogive. Regardless, an epa with an interior epa subtracted is probably the easiest overall to construct (and will be fast to evaluate). Cheers! Sean |