

"clipka" <nomail@nomail> wrote:
> "JayWiz" <nomail@nomail> wrote:
> > The normal lathe uses straight lines to connect the "dots". If a curve could be
> > used then the polyline object from autocad (or TurboCAD which I also use) could
> > be easily translated. The other lathe types are not really condusive to the
> > objects I use.
>
> "Curve" is a bit vague, as all the quadratic_spline, cubic_spline and
> bezier_spline would fall into that category.
>
> I just googled for what type of spline AutoCAD's "polyline" actually is,
> mathematically, only to find that it's not a classic spline at all...
>
> From a geometric point of view, a polyline lathe should be representable as an
> (albeit possibly nontrivial) CSG object composed entirely of linear_spline
> lathes and tori, and a polyline prism as a CSG object composed entirely of
> standard linear_spline prisms and cylinders.
>
>
> So that might be a point for the ToDo list: Implement a new spline type,
> defining a path made up of straight lines and circular arcs.
>
> Question to you as someone familiar with AutoCAD: How's a polyline actually
> defined in AutoCAD? Is it basically a polygon, with corners rounded using a
> standard radius? Is it a polygon with corners rounded using different radius
> for each corner? Or a free intermix of straight lines and arcs?
A polyline is defined using both straight lines and arcs.
AutoCAD uses radial as a default. The user can then redefine the curve by moving
the endpoints, start angle, end angle, and radius. It also has a center point
and a direction. With this information AutoCAD makes a corner. The corner can
be stretched (made eliptical).Perhaps for a general description, the curve
could be an elliptical curve with a circular curve as a special case. AutoCAD
stores the curve as a true curve but when it is extruded it uses a user defined
number of straight faces with smoothing normals to appear curved, which is why
AutoCAD renderings seem of low quality.
I will post a binary view of a sample rendering (with a low resolution) in the
binary newsgroup.
Jay
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