Area moment of inertia...which axis is which?

[dgilmoreJNGSW]

I'm trying to determine the area moment of inertia for a long beam with constant cross section. What Inventor returns is values for "Ix" and "Iy". But it is extremely confusing which principal axes these refer to. I realize they pass through the centroid, but which axis is x and which is y?

Maybe it follows the main, colored axes? Nope. In my example, the y axis comes perpendicularly out of the page, which would be meaningless. So the Iy refers to some other axis. 

Maybe y is the vertical axis relative to the way the sketch is shown on the screen? Nope. If I turn the sketch 90 degrees and re calculate, I get the same values in the same order.

When I look it up online, they say that the "larger" area moment of inertial is given first, as Ix. Well...which axis is larger? For a simple part it might be obvious, but what about a complex part where it might be ambiguous which axis is producing the larger moment of inertia? 

In my case, I think I know which axis would be the weaker one, but it is still sideways to how the sketch is oriented. The larger moment is listed as "Ix", but the stronger axis appears to be the vertical one. How am I supposed to know which axis is which in the answer?

[dan_inv09]

Since you are using Region Properties then it is probably related to the sketch rather than the 3D model's coordinate system. If you go to the iProperties for the whole part then you can see inertia related to x, y, and z. (I must confess that I have never even see, let alone used, the region properties in a sketch.)

There is allegedly some logic to where horizontal and vertical are assigned for a sketch. You could probably try placing a horizontal constraint in your sketch to see where the x goes (or vertical for y).