CircularArc() in 3D

rgoldrich shared this question 1 year ago
Answered

The CircularArc function works well and according to the documentation in the manual. And you can get either the <180 deg or >180 deg arc based on the order in which the points are entered (Geogebra draws the arc counter-clockwise).


In the 3D view, however, the order of the points seems to have no effect, i.e. CircularArc(O,A,B) gives the same arc as CircularArc(O,B,A). In my case, I am trying to get the >180deg arc, and have not figured out a way to do this.


Whether this is a bug or by design, might I suggest that the direction of the arc in 3D should be based on the right-hand rule? (This is equivalent to how it works in 2D). It would bring consistency to the function and would give the freedom (for people like me) to choose either arc.


I am using Geogebra 5.0.625.0-d.


Thank you for such a wonderful program.


R. Goldrich

Comments (5)

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1

in 3D the right hand rule does not ever work. Search the hair sphere theorem.

you can try curve as in attached

Files: foro.ggb
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1

Sorry, excuse

problems found in previous attached

other attached

Files: foro.ggb
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1

Yes, you are correct, of course. I was looking at this all wrong! And thank you for the work around.

Perhaps it makes sense to overload the CircularArc tool for 3D to allow for an additional argument which specifies the desired arc. It would clean things up quite a bit when doing spherical geometry diagrams. (In the meantime, I can make a custom tool for this).

Many thanks again!

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1

do you mean CircularArc(O,A,B,1) or CircularArc(O,A,B,2) ?

with 1 by default?

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1

Yes, exactly something along those lines.

The last argument (optional) would indicate a < or > 180deg arc. Exactly how the last argument should "behave" (like your example 1 or 2) I would leave to people who have a better feel for what fits into the Geogebra philosophy.

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