So, why do you need a single arc for circles?
I have been running this software for over ten years now and have not had the need to force a circle to a single command.
One thing you mentioned is that you are "exporting" the drawing. This would imply that you are using another piece of software in some manner to manipulate that circle. Consider that Vectric produces their software as a CAD/CAM package. The intent is to be able to draw and toolpath without the need for exterior software. That said, I typically use Corel for all my designing because that is what I have used for years and years. Interestingly enough Corel also exports circles with four nodes. So it is not unusual for this to occur. Vectric is obviously not the only one doing it. My guess is that Corel is not going to change.
The more I think about this, the more it makes sense to NOT create a true circle entity. By using four bezier arcs the circle can be stretched into an oval. A true circle entity would not be able to do that since there would be no handles to manipulate it other than radius, and I am not sure that is possible in EPS format.
I have need of generating vectors from various mathematical calculations, external to Aspire, and then loading them into Aspire to create tool paths.
Upon export from Aspire, I'd like to see the exported file contain the vectors I imported, not some close approximation to the vectors.. but the same vectors.
A 360 degree arc (a circle), which becomes a 4-segment Bezier will NEVER match the original circle, as the Bezier is a cubic function, and can NEVER ever fit a circle. It can hit the circle at a few points on the circumference but elsewhere will always be in error.
Better than importing a programatically generated vector file would be that Aspire provide or expose a COM-type automation interface, or document as such, if it is already provided. By that manner, the import/export need would not be needed, as Aspire could be controlled externally, via capabilities that simply are not provided in the interface. LUA script (a gadget) would be an internal corollary to an external COM- automation, however I see no easy way to interface a database (CTree+) which is built into my own generating software.
The simple EPS circle, generated by "arc" contains three parameters: X, Y, Radius (the other two parameters are begin angle, 0, and end angle, 360)
The close approximation to Bezier requires a moveto, then four curveto commands, where two of the parameters (x,y) pairs are locations of the Bezier control points.
If you look at a "circle" created by four Bezier vectors, you'll find that the calculation to locate the "radius" of the "close circle" really isn't one number.. it is a function which produces an infinity of "radii", hence, there is no real circle with the provided implementation.
The best one may do is to calculate a bounding box that contains the four Bezier curves, however, there is no guarantee that the given Bezier curves are aligned on the x- or y- axis. They could be aligned on any angle, and the calculation for the bounding box produces a bounding box with width/height that differs from the expected "circle" diameter.
A simple "arc" of 360 degrees or 0..2PI or true circle is neded for my purpose.