Angle from xy plane definition

[MJLM]

When I draw a line from 0,0,0 to -3,-4,-5 and checking for the "angle from XY plane" through the list command, I get 315 deg instead of 225 as I would expect. When I draw the line from 0,0,0 to 3,4,5, I get as expected 45 deg. Can somebody help me understand how this 315 angle from XY plane is defined?

 

Thank you.

[BIGAL]

Look at UNITS one option is direction anti or clockwise, another is the 0 direction. Depending on end picked angle will be 180 different also.

[SEANT]

12 hours ago, MJLM said:

When I draw a line from 0,0,0 to -3,-4,-5 and checking for the "angle from XY plane" through the list command, I get 315 deg instead of 225 as I would expect. When I draw the line from 0,0,0 to 3,4,5, I get as expected 45 deg. Can somebody help me understand how this 315 angle from XY plane is defined?

 

Thank you.

Why would you expect 225? 

 

Another way to think of 315 degrees is -45 degrees.  

[MJLM]

Thanks but I was under the impression that the angles are measured such as this. That s why I was expecting 225.

[MJLM]

It still to me unclear what is the reference point for this 3D angle. That is, what is the starting vector or axis.

[SEANT]

The vector listed in the " Angle In XY Plane" is used as the base vector.  Think of it as the reference "X axis".  In the default setup for AutoCAD, the X axis is the base for angle measures, and the positive direction is towards the positive Y quadrant.

[SEANT]

similarly, the positive direction is towards the positive Z direction (Counterclockwise).

[SEANT]

Like this.

[CyberAngel]

Here's another way of looking at it. When AutoCAD calculates the "angle from XY plane," it only looks at the endpoints, and it ignores the X and Y coordinates. The first line, from (0,0,0) to (3,4,5), has one end at Z=0 and the other 5 units away at Z=5. That's a right equilateral triangle with both sides at 5. The other line, from (0,0,0) to (-3,-4,-5), has one end at Z=0 and the other 5 units away at Z=-5. It's the same geometry only in reverse. If you draw a line from (3,4,5) to (0,0,0), you get 315 degrees also.

 

Visually, imagine the line as lying on a plane that is orthogonal to the XY plane. The angle is measured on that plane, with the start point as the origin. If that line happens to lie on the XZ or YZ plane, it's easier to see how it works.