# Thread: Rotation of major and minor axis? (circle)

1. ## Rotation of major and minor axis? (circle)

Hi guys, say a circle (let's assume it's a perfect circle) was rotating in the exact same spot in two point perspective. Since, I heard all circles are ellipses in perspective... would the major and minor axes change? :0 Or would they stay the same? ._. assuming it's a perfect circle...
And if the axes do indeed change, how would I go about replotting the circle? O_o

I skimmed through the loomis successful drawing perspective section and didn't see a part for axis rotation .0.

2. Do you know why a circle is an ellipse in perspective? If you know this, then you will know that an ellipse stays the same shape in the same orientation when the actual circle is rotated.

Take a piece of paper, draw a circle on it. Lower your head to the plane of the paper. Rotate the paper. Did the ellipse change major and minor axes? The circle has rotated, but it would still look like an ellipse with the major axis perpendicular to your line of sight. In fact, any circle in front of you is an ellipse with the major axis always perpendicular to your line of sight.
Last edited by Vay; November 11th, 2012 at 11:39 PM.

3. Hey Vay! I was racking my head over it trying to imagine how it would be :0 I know if it were uneven for sure it would change, but the circle confused me. Thanks for the clarification, explained it in a way I hadn't thought of

The circle appears to be an ellipse because the plane appears to be tilted or something xD

the Major and Minor axis of an ellipse simply represent the length and width of an ellipse, respectively.

Long clunky version--In the context of ellipses, a circle is a 90° ellipse, when its plane is seen perpendicular or 90° to your line of sight. The Major Axis of an ellipse represents the diameter of the circle it represents. The Minor Axis represents the foreshortened length of the diameter of that same circle, when the circle is rotated to less than 90° in relation to the line of sight. The Minor Axis equals the sine of the angle, rotated from from 0° (a circle edge on to your line of sight, appearing as a line), multiplied by the circles diameter.
Last edited by bill618; November 12th, 2012 at 03:21 PM.

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