Pitch Gauge

Hi everyone,

My new vehicle is almost ready for sale, but there's just one thing I haven't been able to figure out. Since it is a mouselook vehicle, and sometimes you get confused when piloting and end up pointing up in the sky, with no ground frame of reference, I added a graphical pitch gauge.

The problem is the math, of course

Right now, in one of the root prim scripts, I have the following code:

vector rot = llRot2Euler (llGetRot ());
float pitch = rot.y;

Unfortunately, this works fine when the vehicle is facing east, but it is backwards when facing west. I understand what the problem is, but I don't have enough gut feel for how quaternions work to know how to fix it. I want a value, in degrees or radians, that represents the vehicle's pitch with respect to the world axis, independent of heading.

Does anyone have a solution to this?

I will give a free copy of my vehicle (the Marlin XS-1, which has a $500 price tag) to the first person who posts a solution that works...

Thanks,
Jon

It's not a full solution (and I can't get in world), but if facing east gives you the right pitch I guess you need to look at the z component of the Euler (I don't understand quaternions well enough either).

If that's between +/- pi/2 on the positive side then use the straight formula, if it's outside that range just multiply by -1.

Best bet, probably, cos of the z angle. Mutliply by the sign of the cos - that works out to be the same.

I've not tested this at all btw, the way SL converts quaternions to eulers might mean this doesn't actually work, but the maths is sound enough.

That fixes the east/west problem, but it still goes flat when facing north and south...

I'm going to try a variation, I'll let you know.

- Jon

Still nobody with any ideas???

- Jon

There must be a simple answer to this, but I'm just not seeing it.

I can suggest a kludgy one though -

If you're between ±45º or ±135º around z use the angle around y and the sign (±) of the cosine of the angle around z. From 45 to 135º and -45 to -135º around z use the angle around x and the sign of the sine of the sin around z.

You might have to play with the signs of these and you will probably find it jumps a bit as you swing past the 4 semi-cardinal points but it should at least give you an element of control and feedback.

It's nights like this that make me remember why I never took to 3D geometery! I have a sneaky suspicion that either quaternions give you a dead easy way to calculate it, or you've got to do something with a x product of the vectors.

This was writen by another scripter in this forum a while ago.

vector getRollPitchHeading(rotation test)
{
    vector v=llRot2Fwd(test);
    float heading = llAtan2(v.y, v.x);

    float run=llSqrt(v.x * v.x + v.y * v.y);
    float pitch = -llAtan2(v.z, run);

    rotation y=llEuler2Rot(<0, pitch, 0>);
    rotation z=llEuler2Rot(<0, 0, heading>);
    rotation x=test / z / y;
    vector tmp=llRot2Euler(x);
    float roll=tmp.x;

    return <roll, pitch, heading>;
}

i would make this change, because we know v is a unit vector.

    float run=llSqrt(v.x * v.x + v.y * v.y);
to
    float run=llSqrt(1 - v.z * v.z);

Strife -- you got it...

I've dropped your reward into your inventory. Enjoy!

- Jon