I recently downloaded the new build of Rhino for Mac. I believe I have found an issue with the Analyze Angle command. I was measuring both interior and exterior angles and noticed that the sum of the angles does not total 360 degrees. I was able to accurately measure the interior or smaller angle by drawing 2 lines that started from the center origin of the angle.

My problem arose when I tried to measure the exterior or larger angle. I chose to Analyze Angle and started my measurement lines from the outer edge of the radius into the center origin. The resulting analyzed angle seemed to be 180 degrees less than the true measurement. Is this assessment correct?

I’ll have to get out my Mac and test, but just to be sure:

Analyze>Angle with four points is actually measuring the angle between two vectors, the first vector is determined by the first pair of points you click, and the second vector is the second pair. The angle will never be more than 180° or less than 0°. The ORDER in which you pick the points is important, it will give different results if you invert the pick order of one pair.

You can imagine it graphically this way: the first two points determine a line, with the first point as its start point. The second pair makes another line whose start point is the first pick on that pair (the 3rd point pick). Both lines are then translated so their start points are at the origin and then the angle is measured from there…

Hi Mitch,
Thanks for the explanation of Analyze>Angle. I am almost positive that the Mac Analyze>Angle is off by 180 degrees. Give it a try and let me know what you think.
Eli

OK, after having downloaded and installed the latest build (487) I made a few lines and measured the angles between them… It appears to act exactly like the Windows version… I cannot make it find an angle of less than 0° or more than 180°… Perhaps you can post a file with instructions on how to reproduce what you’re seeing?

This is why the analysis does not match your expectation. You are defining two vectors, both with different origins. Rhino will nevertheless analyze the angle between them as vectors, i.e irrespective of the origin, which result in an angle 180 degrees less than what you expected.

Now that I read your post and went back and re-read the original, your analysis is most likely correct… What Eli is seeing is the complement of the angle (180-angle) rather than the angle itself. If the pick order is inverted, the angle should be correct…

But it then will be the interior angle. As you said, Rhino cannot measure angles > 180 deg. (since the angle between two vectors cannot be more than that, i.e. pointing in opposite directions)

Yes, I guess I just didn’t read the terminology right - if by “exterior angle” one means the angle more than 180°, then yes, you can’t get that with the Analyze>Angle command, only with a dimension object (which you can pull either way to go “interior” or “exterior”)…