Heading of my Y-axis at 90° pitch?

[Zatnikitelman]

It should be clear by now that I stink at coordinate conversions . Again, I'm having trouble with knowing how to convert. This time, I need to find what heading my Y-axis is pointing to while my Z-Axis points at the Zenith. Orbiter has the HorizonRot() function, but I'm not exactly sure what that would give me. How do I find the heading of my Y-axis when the ship is vertical?
Thanks for any help,
Zatman

 

[ar81]

Imagine the universe flipped right and left. This is the universe of Orbiter and DirectX.

 

[SiameseCat]

I think you could use

VECTOR3 v;
HorizonRot(_V(0, 1, 0), v);
double angle = PI-atan2(v.x, v.z);

The HorizonRot function will convert the y-axis vector to horizon-relative coordinates, so v will be in the xz-plane. Then, you can use atan2 to get the angle between the vector and the x axis. If you're heading is 00, the y-axis will be (0, 0, -1) in the horizon frame, so you need to subtract the result from 180 degrees to correct for this.

The code above should work, but I haven't tested it, so there might be a subtle mistake (i.e. signs) somewhere.

 

[Zatnikitelman]

Thanks SOOO much SiameseCat! I had to multiple by Orbiter's DEG, then subtract 180 from it and toss in an If statement to get heading from 180 to 360 properly so the final code looks like this:

VECTOR3 v;
HorizonRot(_V(0,1,0),v);
double angle = (PI+atan2(v.x,v.z))*DEG-180;
if(angle<=0)
   angle+=360;

Again, thanks so much for the help. Eventually, I'll figure this stuff out.
Thanks!

 

[SiameseCat]

You can change the third line to

double angle = atan2(v.x, v.z)*DEG;

Adding Pi and subtracting 180 degrees will cancel each other out (taking into account radian to decimal conversion).