I think what he was looking for was that drawing program type node where all the "points" are actually "on" the curve, and they each have "2 handles" (points) that pull out and away from the point to create the curvature. These points can be broken up so the handles work symmetrically, asymmetrically, or "converted to corner point", where they then are allowed to break curvature....

It really is a mess though when trying to work.

Hi Burr,

> I think what he was looking for was that drawing program
> type node where all the "points" are actually "on" the curve,
> and they each have "2 handles" (points) that pull out and
> away from the point to create the curvature.

Yeah that is what is called a "Piecewise Bezier" curve type structure.

It's not very good to use for things involving surfacing though, because that kind of a curve is not very smooth - it's made up of a bunch of little 4-point curves that are touching one another and each of those curve pieces are only tangent (G1) to one another and not curvature continuous to one another.

It tends to be harder to see this lack of smoothness when you are only looking it as a 2D outline. Once they are used as a basis for building a surface where the normals are more apparent through shading or reflections the curvature breaks can become more visible.

The NURBS curve method that MoI uses was basically invented specifically to solve this problem and to get a higher quality and smoother type of curve, where there can be more than just 4 points in a single smooth curve piece.

Personally I think the NURBS method is a lot better for 2D curve drawing as well though, because it behaves in a more predictable and uniform manner, the Bezier drawing method involves a kind of strange "bulge things out while drawing" type method while the NURBS curve drawing method lets you move more kind of forwards point by point as you are drawing.

- Michael

Hi Michael,
I was actually just responding to a guy in another forum who is having difficulty with "Corel Type" geometry in a Cad/CAM software.

It becomes apparent there as the calculations of the machining break down on the imported geometry with regard to "connectivity of the defined curves and tolerance settings of some contour functions".

Thanks for the info....

Hi Burr,

> I was actually just responding to a guy in another forum who
> is having difficulty with "Corel Type" geometry in a
> Cad/CAM software.

That may actually be due to a different problem yet.

One other thing that is not too unusual with 2D drawing programs is to make one of those 4 point curve segments be set up with the first 2 points stacked up right on top of one another.

That somewhat degrades the mathematics that is operating behind the curve definitions, and that kind of "stacked up" / duplicated points can cause problems with various CAD/CAM programs that want to do some more sophisticated processing of the curves.

It may be due to a choice by the user making the 2D drawing data to use a particular node type on the starting node of a curve like "collapsed start" or "collapsed end" maybe something like that. They might want to avoid that kind of node type and instead make sure they have a visible tangent handle on every spot.

- Michael

Thank you. Very good information.

Hi Michael,

Just back online - Your discussion with Burrman all seems logical. I understand the limitation with point bezier lines so your suggestion of picking a node and making it a corner is good for me.

Thanks, Matt