# How does Rhino decide which direction is positive or negative rotation?

I run into this little issue all the time of trying to rotate geometry a specific degree, and inevitably the 20 degrees I want to rotate is the wrong way! It’s never intuitive to me which direction it will decide to make positive or negative. Is there an easy, logical method to follow so I don’t have to input my rotations twice all the time?

Hello - for Rotate, the CPlane Z axis is the axis and + rotation is in the counter-clockwise direction. For Rotate3D, the axis goes from first point to second point and that vector becomes the equivalent of the CPlane Z in Rotate , so + rotation is counter clockwise if you are looking down that axis from its end to its start…

-Pascal

perfect, thanks for the explanation. I appreciate the quick reply!

May I know what do you mean about looking down that axis from its end to its start? Could you please help post an image here to explain it? thanks a lot.

Rhino uses the “right hand rule” for coordinates.

Hold your right hand out straight vertically…that’s the direction of the X axis.
Rotate your thumb so that it’s pointing 90 degrees from your other fingers. That’s the Y axis.
Close your fingers and make a “thumbs up”…the thumb pointing up is the Z direction, and the direction you rolled your fingers to close them is “positive rotation.”

Thank you so much Jim

So both rotate and rotate3d commands follow the positive rotation is counter-clockwise?

Yeah…of course predicting which way is going to be +ve on a rotate3D still takes some practice.

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