Position Vessel loaded from ProtoVessel

[allista]

I'm working on a plugin in which I need to spawn a Vessel from a previously saved ProtoVessel, but with the new orbit position and rotation.

I've tired to change these parameters on a spawned vessel with no effect: position and rotation stay the same as they were in the protovessel, no matter what.

If I try to set them on the protovessel itself, position is set correctly, but rotation, when I load the protovessel, changes again in a pattern I cannot understand.

Could anyone explain to me how to correctly set the precise position-rotation-orbit of a vessel? Any help is highly appreciated!

[Yilmas]

You shouldn't need to set the rotation directly... Have a look at Orbit and OrbitDriver...

Set the orbit and use:

vessel.orbitDriver.pos = vessel.orbit.pos.xzy;
vessel.orbitDriver.vel = vessel.orbit.vel;

[allista]

Thanks, I'll look into it.

Yet, this sets the position and velocity, not the rotation. But I also need to tell the vessel where is FRONT and where is UP.

[Yilmas]

Rather than telling it directly where to look, I recommend you to mess around with the orbit of the vessel, when setting an orbit for a vessel, you automatically set its position and rotation...

http://en.wikipedia.org/wiki/Orbital_inclination#mediaviewer/File:Orbit1.svg

[allista]

I'll do as you recommend.

But I still can't understand how the orbit describing the movement of a point object which does not have a direction, may describe directions of the axes of the 3d-object which this point represents. I mean, the vessel's head may be directed anywhere, and the orbit will stay the same. Thus you cannot derive this direction from the given orbit. Am I missing something obvious?

[xEvilReeperx]

But I still can't understand how the orbit describing the movement of a point object which does not have a direction, may describe directions of the axes of the 3d-object which this point represents. I mean, the vessel's head may be directed anywhere, and the orbit will stay the same. Thus you cannot derive this direction from the given orbit. Am I missing something obvious?

No, you're right: the vessel's orbit doesn't have any meaning to the vessel's actual orientation. You can use Vessel.SetRotation to orient it in a particular way. Can you show a snippet of code demonstrating what you're trying to do and describing how it's wrong?

[allista]

OK, I've kinda "figured" out the orientation part.

The thing is: vessel.vesselTransform.rotation and vessel.protoVessel.rotation are not the same; orientation of a vessel is stored in its protoVessel with respect to some other reference frame. So, in order to set a correct orientation of a vessel upon its loading from protoVessel, one needs to combine the desired rotation with the rotation between reference frames:

//these values are predefined
ConfigNode config_node;
Quaternion desired_rotation;

//get needed rotation quaternions
Quaternion vessel_rot = this.vessel.vesselTransform.rotation;
[B]//it is essential to use BackupVessel() instead of vessel.protoVessel, because in general the latter does not store the current flight state of the vessel[/B]
Quaternion proto_rot = this.vessel.BackupVessel().rotation; 

//recreate a protovessel from a config node
ProtoVessel pv = new ProtoVessel(config_node, FlightDriver.FlightStateCache);

//set protovessel rotation
[B]pv.rotation = proto_rot*vessel_rot.Inverse()*desired_rotation;[/B]

//load the vessel from protovessel
pv.Load(FlightDriver.FlightStateCache.flightState);

//check the rotation
Debug.Log(string.Format("desired rotation: {0}", desired_rotation.eulerAngles));
Debug.Log(string.Format("actual rotation: {0}", pv.vesselRef.vesselTransform.rotation.eulerAngles));

I still can't position the loaded vessel correctly with respect to the given orbit though. But the reason seems the same, so I'll dig more...

xEvilReeperx, unfortunately, I can't SetPosition() or SetRotation() of the pv.refVessel until it is fully loaded with FlightGlobals.ForceSetActiveVessel(pv.refVessel). And then it could be done only with a waiting coroutine, but this fails for an unknown reason: the coroutine just hangs after the first yield.

Edited June 22, 2014 by allista
Bug fix in the code snippet =^_^=

[allista]

And the trick with positioning was to (shame on me) carefully read the API docs for Orbit class:

NOTE: All Vector3d's returned by Orbit class functions have their y and z axes flipped. You have to flip these back to get the vectors in world coordinates.

Switching the y and z components of the vector difference between the vessel.findWorldCenterOfMass() and the desired_position gave me the correct position of the spawned vessel:

Orbit this_orb = vessel.orbit;
Orbit new_orb = new Orbit();

Vector3 d_pos = desired_position-vessel.findWorldCenterOfMass();
Vector3d new_orb_pos = this_orb.pos+new Vector3d(d_pos.x, d_pos.z, d_pos.y);

new_orb.UpdateFromStateVectors(new_orb_pos, this_orb.vel, this_orb.referenceBody, Planetarium.GetUniversalTime());