3d doubt

Periodic curves, those great unknown…what are they? Any interest? (why would anyone want to make a curve periodic?)

because… they don’t have anything better to do?!?

Are you ok?

i’m very ok.


reminder: answer the question if able. be polite. minimize sarcasm. cant do that? stay in the Unregistered sections.

ONO: check PM.

What is PM? :neutral_face:

Private Message

aw, ykh, didn’t your mother teach you to share?!

anyway, periodic curves have the end and beginning connected. alias tools sometimes call them closed. periodics make many cad systems unhappy, particularly solid modeling apps. the stitch tool has a fuction that breaks periodic curves to make them more palatable when exported to foreign 3d apps.

two reasons tbh. first, generic question meant generic and technically confusing answer (for me too). second is i wasn’t (and still am not) sure of my answer. so rather than post confusion, i kept speculation private. but it was this -

periodic curves are just repeating functions. waveforms (like sound). and they’re accurate. expect CAD actually prefers a straight mathematical formula. but bc its rigidly defined and not an algorithm, its not quite as flexible. but still pretty good. Fourier showed really complex waveforms can be broken down into simpler sine/cosine functions.

but there is an issue now i think about it and didnt mention in PM (and i’ve seen similar issue occur in Pro/E w simple patterns using angular variables): CAD needs defined limits for periodic functions. bc periodics are sine/cosine, if you go from 359deg to 0deg, most CAD will probly freak. function wants to repeat itself (periodic). overlap. CAD wont like that. which is why i suspect you “break” it before you export it to CAD. from Alias website:

some CAD systems experience issues with the importing and handling of periodic geometry. To address these issues, enable the Periodics option found in the Check Model Parameters chapter of the Check Model Settings option box. Surfaces and curves of a revolutionary character may be considered periodic geometry. A method for changing their behavior is to detach the geometry from the items and > create a beginning point and an ending point.

i’d like to hear a mathematician explain it in layman’s terms. no doubt i’m still missing something.