Hi,

Guest

JB

Jordan Brown

Fri, Apr 23, 2021 11:24 PM

On 4/23/2021 4:17 PM, Jordan Brown wrote:

On 4/23/2021 4:03 PM, Sayandeep Khan wrote:

How can we extract such faces from a shell given some conditions?

I'd be happy to cook up a demonstration, but I don't have time right now.

Here's the basic theory...

Have you looked at how you build a polyhedron? You define a bunch of

points, and then you connect groups of those points into faces that

all add up to being the polyhedron.

The idea here is that you're going to build a polyhedron that mostly

looks like a cylinder a bit bigger than the cylinder that you're going

to cut, except that the top of this polyhedron is wavy, using your

Bezier curve.

[ And on autopilot I hit Ctrl+Enter and sent the message when I wasn't

ready to... ]

If you have N points in your Bezier curve, you're probably going to have

3*N, or maybe 2*N+1 faces:

- Your top surface is a bunch of triangles with their outside vertices

along the Bezier curve that's wrapped around the cylinder, and the

inside vertex at the center of the cylinder at some

middle-of-the-road Z value - The shell is a bunch of quadrilaterals with those same outside

vertices as the top vertices, and the bottom vertices being those

same X/Y values and Z just below the base of the cylinder to be cut. - The bottom surface might be a set of triangles similar to the top

surface, but all with that same just-below-the-base Z value, or

maybe you can do it as one big N-gon.

Doing this is a bit intricate, but isn't all that *hard* once you get

the pattern down. Mostly it's a bunch of list comprehensions, and some

light trigonometry to walk around the circumference of the cylinder-like

polyhedron that you're constructing.

On 4/23/2021 4:17 PM, Jordan Brown wrote:
> On 4/23/2021 4:03 PM, Sayandeep Khan wrote:
>> How can we extract such faces from a shell given some conditions?
>
> I'd be happy to cook up a demonstration, but I don't have time right now.
>
> Here's the basic theory...
>
> Have you looked at how you build a polyhedron? You define a bunch of
> points, and then you connect groups of those points into faces that
> all add up to being the polyhedron.
>
> The idea here is that you're going to build a polyhedron that mostly
> looks like a cylinder a bit bigger than the cylinder that you're going
> to cut, except that the top of this polyhedron is wavy, using your
> Bezier curve.
[ And on autopilot I hit Ctrl+Enter and sent the message when I wasn't
ready to... ]
If you have N points in your Bezier curve, you're probably going to have
3*N, or maybe 2*N+1 faces:
* Your top surface is a bunch of triangles with their outside vertices
along the Bezier curve that's wrapped around the cylinder, and the
inside vertex at the center of the cylinder at some
middle-of-the-road Z value
* The shell is a bunch of quadrilaterals with those same outside
vertices as the top vertices, and the bottom vertices being those
same X/Y values and Z just below the base of the cylinder to be cut.
* The bottom surface might be a set of triangles similar to the top
surface, but all with that same just-below-the-base Z value, or
maybe you can do it as one big N-gon.
Doing this is a bit intricate, but isn't all that *hard* once you get
the pattern down. Mostly it's a bunch of list comprehensions, and some
light trigonometry to walk around the circumference of the cylinder-like
polyhedron that you're constructing.

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