[SOLVED] Upwards rotation on planet, knowing only latitude and longitude?

[Rahjital]

I'm creating a new ship through ProtoVessel.CreateVesselNode. I managed to place it correctly on the ground and got rotation to work properly, which I tested by using data from vessels saved in persistent.sfs.

The next step is to get this working for any point on the planet, and that's where I got stuck. No matter how I try, I can't get the ship to point upwards like a proper rocket should. How can I calculate the rotation quaternion to point the ship upwards for any latitude and longitude on a celestial body?

Edited November 13, 2016 by Rahjital

[Boris-Barboris]

https://docs.unity3d.com/ScriptReference/Quaternion.SetLookRotation.html

current position - planet position = up vector

view vector doesn't really matter for rocket case, pick any orthogonal to up vector.

Edited November 12, 2016 by Boris-Barboris

[Rahjital]

Thanks! I've already tried that, among other things. This is how it looked:

Vector3d upAxis = FlightGlobals.getUpAxis(planet, planet.GetWorldSurfacePosition(latitude, longitude, altitude));
Quaternion rotation = Quaternion.LookRotation(upAxis);

(FlightGlobals.getUpAxis does exactly what you said, and then normalizes the vector.)

And this is the result ingame:

Spoiler

 

I suppose the vector could be somehow manipulated to yield the correct rotation, but I'm at a loss how to do that correctly...

[Crzyrndm]

That's KSP's vessel rotations at work. Always remember that vessel.transform.up is the direction your vessel is pointing in (lets call it vessel.forward) . On the other hand, the default "no rotation" quaternion indicates vessel.transform.forward (vessel.up * -1, aka vessel.down)

Any time you're dealing with vessel rotations, the following transform becomes very handy

// NOTE: Quaternion maths is not commutative. You can't change the order of operations and get the same result!!! (x * y != y * x)
Quat vesselrot = upRot * Quaternion.Euler(-90, 0, 0); // rotate the direction 90 degrees about the x (right) axis. May be 90 or -90, I haven't checked

 

Edited November 13, 2016 by Crzyrndm

[Boris-Barboris]

13 hours ago, Rahjital said:

And this is the result ingame:

If you would examine the function prototype, you would see that the way you do it assigns upVector to view. It is not what you need.

Edited November 13, 2016 by Boris-Barboris

[Rahjital]

Got it to work, thank you both! Turns out that apart from having to fix the LookRotation, rotation for landed vessels is relative to the planet's transform, rather than global. The solution ended up being this:

Quaternion rotation = Quaternion.Inverse(planet.bodyTransform.rotation) * Quaternion.LookRotation(northAxis, upAxis);

 

Edited November 13, 2016 by Rahjital