How is circle orientation determined?

Alejandro_Ogata1 · July 30, 2019, 5:50am

I am working on a “foldable geometry” piece and I am trying to understand how I can determine the orientation of a circle. (meaning, where is the start point of the curve)
When drawing a circle by center/radius it appears to use the world XYZ with the starting point at the 3 o’clock quadrant and then moving counterclockwise.
Since the geometric basis prevents me from using a Circle by points (presumably one of those points would be the origin), I thought that the circle by Plane Radius would make the circle inherit the plane orientation.
On the example (and image) attached, it appears to do so for the first couple of circles. But then on the fourth & fifth circle it appears to ignore the plane orientation.
Any thoughts on how else I could control the orientation of the circle, knowing that it will be rotated in 3 dimensions?

circleOrientationDyn.dyn (84.2 KB)

Mostafa_El_Ayoubi · July 30, 2019, 5:50am

Hi @Alejandro_Ogata1 , you should counsider using Coordinate systems and Transform

Also, you can get the context coordinate system of each circle like this:

Alejandro_Ogata1 · July 6, 2016, 10:10pm

That worked great! thanks

Vikram_Subbaiah · July 30, 2019, 5:50am

Alejandro_Ogata1 · July 30, 2019, 5:50am

Thank you Vikram and Mostafa.
Both solutions worked great. (see attached if curious what this was all about)

Now, despite the fact that my problem is solved, I remain interested in understanding how a circle derives its orientation at creation point.
Some of my basic testing shows that the orientation does respond somewhat to the creation method (in this case circle by plane). Meaning that it does derive some data from the plane. However, it appears that the info is not the exact coordinate system of the plane,
Furthermore, as the circle is rotated off-plane, there is an abrupt change in the orientation. See difference between flat circle set (0 degree rotation) and rotating circle set (5-degree rotation, off-plane). Also note, that the abrupt change only occurs when shifting from planar to off-plane rotations. (changes become predictable at all other rotation angles)