If you haven’t had calculus, and you’re interested in understanding CAD topology on a deeper level, I recommend taking a crash course in Calc I.

http://adam.theoherns.com/2010/03/10/simple-graphic-trainer/

As for degree, just stick with 2 or 3 unless you have some specific reason for going higher. Use degree-2 when you want a purely-convex curve or surface, and degree-3 when you need more complex curvature across the curve/surface. Most spline tools default to degree-3. Many CAD tools only support degree-3.

CAD packages all really do the same things mathematically. There are some relatively important mathematical differences (e.g. is a cube defined as an origin, width, height and depth, or is it defined as six individually-defined planes?), but in reality the differences in CAD packages have more to do with user interface preferences than actual math. Mathematically speaking, a spline is defined as a polynomial, and solved for display using basic 3D calculus. From the user standpoint, however, a spline can be defined a million different ways. You just have to choose the method that works best for you.

Good luck!

As for my “true” NURBS comment now that I wiser and more educated I probably wouldn’t have made it. Although now that understand what makes up a NURBS curve better you can see where some programs,like Autocad, have a spline tool, and if you look at the help menu it says “Create splines, which are NURBS curves, with SPLINE” but don’t allow you to control the degree of the curve like other NURBS packages do.

Your question about the difference between G1,G2 etc and degree 1, 2, etc is valid. “G1″ refers to the relationship between two different curves at a point (i.e. they have the same direction at said point). “Degree 1″ refers to the interpolation method by which a given curve is drawn. ‘G’ values refer to relationships between curves or surfaces, where ‘degree’ values refer to how a curve itself is drawn.

The two concepts (‘G’ and ‘degree’) are related, but not in any easy-to-explain way. It is theoretically possible for two degree-2 curves to have G3 continuity at the point of intersection (albeit highly unlikely). It’s also easy to have two degree-7 curves that end up with only G0 continuity at the point of intersection.

As for the definition of a “true” NURBS modeler, I don’t buy into those kinds ill-defined labels. Any modeling package that utilizes Non-Uniform Rational B-Splines in 3D space is a NURBS modeler. You’ll choose the tool that’s right for you depending on what feature/interface/price trade-offs you’re willing to make.

Don’t become a victim of the “more is better” mindset when it comes to continuity. I use good ol’ tangency with good ol’ degree-2 curves whenever I can possibly get away with it. I’ll only add geometric complexity (i.e. higher order curves or G2, G3, etc) if I absolutely have to in order to achieve the desired visual result. KISS method!

I’m actually going the opposite direction with it; my next trick will be to make a moving target speed, so that you have to pay attention. That way you can do hills and intervals, and the timer reset thing is just incentive to keep at it. If you have any other ideas for how to motivate me to keep going strong, I’d love to hear them!

Sounds like you’ve got a pretty cool rig going. You should document it sometime and post it up on the web somewhere. Maybe when I do my next release of the software I’ll add a photo tutorial as well.

I also made some minor modifications to the processing code (basically stripped out the target speed functionality).

I’ll let you know if I fix the issue and may play with it a bit more later this week.

Steve

As for your issue with stopping, for some reason I’m not able to replicate it on my end. If it stops getting signals, the graph should drop. Hmmm… unless… could you do me a favor and try swapping the poles of the reed switch on the Arduino for me? Theoretically that might do what you’re describing I think, but I thought I’d tested for that already.

Do let me know what you figure out, and I’ll take a closer look later today as well.

Adam

Works wonderfully. I hadn’t used processing before and was foolishly trying to write a display for my speedometer using Perl/Tk!
This is a much nicer solution.

I have noticed an issue where the software isn’t detecting when the wheel stops turning – try pedaling really fast and then slam on the brakes, the speed will remain constant even though the wheel has stopped moving.

Steve

Eric