Hi,
here’s an example of creating Bezier curves in Tcl (sorry, the comments are in
in French).
Just copy and paste this script into a .tcl file, then select load it via the
menu: File -> Load Script.
Cheers,
Philippe
---------------------------------------------------------------------
# Nom: square2.tcl
# Base : square2.g
Z
kill bez0.sk
# Mettre le grid en mm
# A {1 0 0} B {0 1 0} = x,y Top
# A {0 1 0} B {0 0 1} = y,z Front
# chaque x, y mesure une unité
# O 0 : counter-clockwise, O 1 : clock-wise
# L 1 : left of line (inside box), L 0 : right of line (outside box)
# R : rayon du cercle
# pour les bezier, il faut que la valeur de D soit inferieure de un, au nombre
de points
put bez0.sk sketch \
V { 0 0 0 } A { 1 0 0 } B { 0 1 0 } \
VL { \
{ 0 0 } { 1 0 } { 2 0 } { 3 0 } { 4 0 } { 5 0 } { 6 0 } \
{ 6 1 } { 6 2 } { 6 3 } { 6 4 } { 6 5 } { 6 6 } \
{ 5 6 } { 4 6 } { 3 6 } { 2 6 } { 1 6 } { 0 6 } \
{ 0 5 } { 0 4 } { 0 3 } { 0 2 } { 0 1 } \
{ 1 1 } { 5 1 } { 5 5 } { 1 5 } } \
SL { \
{ line S 1 E 5 } \
{ line S 7 E 11 } \
{ line S 13 E 17 } \
{ line S 19 E 23 } \
{ bezier D 5 P { 0 4 8 10 14 18 } } \
}
B bez0.sk
---------------------------------------
Le 14 oct. 2014 à 05:34, Christopher Sean Morrison <brl...@mac.com> a écrit :
>
> On Oct 13, 2014, at 11:08 AM, Cook, Kathy <kathy.c...@lmco.com> 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
>
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