3d curve anyone?

anyone know how to draw a 3d curve, or have a lisp that might do so?

MKH

 

not very complex.
I have a drainage swale that is going to be cut around a round water storage
tank and I was wanting to draw it in 3d. Makes it nice when you want a spot
elevation at a certain place. Just id near it.

Mike

 

Sounds like what you need is a spiral. A "real" spiral is continuously
curving in two directions at once, and I don't think AutoCAD can do that.
You could approximate it with a 3D polyline, whether with short arcs or line
segments.

It probably wouldn't be too hard to program something to generate a
spiraling series of points (basically like a circular array with
successively changing Z coordinates), and you could then connect them with
3D polyline segments. Would that work for you?

 

yes that would work. I'll google and see what I can find.

Mike

 

Come to think of it, it would be just as easy to program something to make
that 3D polyline (or series of 3D lines) directly, and skip the points.
Specify things similarly to the options for an arc that involve a center
point, plus angle between calculated points (or number of points), vertical
increment between points (or total vertical differential), and direction in
which it rises (or falls). Use (polar) from the center point for successive
points, using a constant distance and incrementing the angle and the Z
coordinate each time.

 

Start with a 2D arc, then ToolPac > Convert > Arc > To 3dPoly.

Terry

 

Dang Terry.......you got me again! Toolpac is awesome.

Mike

 

If the thought here is to convert a single 2D arc into a single arc segment
of a 3D polyline, and then raise one end of it (similar to drawing an arc in
a skewed UCS), then you're not going to get a spiral out of it. In your
drainage swale example, if it goes halfway around the tank, and it's defined
by a single skewed arc or 3D polyline arc segment, it's going to have zero
slope at the ends, and the steepest slope in the middle, and gradually
varying slope in between. If you want anything like what a drainage swale
should really do (slope equally all around), you need an approximation of a
real spiral, with multiple short arcs (or even lines if they're short
enough, like small-increment Sketch), whether independent or as segments of
a 3D polyline.