SetWorldVelocity relevant to surface

[nahkranoth]

*Edit title: I meant Relative to surface

Could someone clearify for me how the axle system works in KSP.

Say I would like to move a ship into a certain direction (say the runway for example)

how would I know what the Vector3D variables should be.

I understand that the ship is standing on the surface and that the vector3D is not an axle that's determined by the surface itself.

So I need to get the Vector3D of the body I'm on and use that for replotting my ships direction.

I looked it up at http://wiki.kerbalspaceprogram.com/wiki/API:CelestialBody

But couldn't really find what I was expecting.

Also I'm not sure how to get just one axle of an Vector3D. Something like Vector3D.x does not work.

public void Update(){
	 this.vessel.SetWorldVelocity (x?,y?,z?);
			}
		}

Would be a happy man if someone could explain it to me.

Edited January 27, 2014 by nahkranoth

[nahkranoth]

Figured out that I could use the rigidbody.AddRelativeForce() to apply a force in a relative direction.

The problem is that the vessel will destroy itself, because I want to accelerate it quickly and the forces get too big.

I have noticed that SetWorldVelocity does not destroy my craft because it does not apply a force to the rigidbody.

I have also found the rigidbody.rotation and I found something about converting that Quaternion.eulerAngles soo I could

get the rigidbody's rotation too the world and apply it to the SetWorldVelocity in theory.

In practice I haven't got that working.

[nahkranoth]

Aha, I got it working thanks to reading.

http://wiki.kerbalspaceprogram.com/wiki/Module_code_examples#Useful_geometry_stuff

As for the runway, just apply the eastUnit to the SetWorldVelocity().

But! off coarse the next problem arises. As I start accelerating to around 700 m/s just above the surface of kerbin my ship just disappeares. I can see an error in the log:

NullReferenceException: Object reference not set to an instance of an object
  at KerbalScript_1.testModule.OnStart (StartState state) [0x00000] in <filename unknown>:0 

  at Part.ModulesOnStart () [0x00000] in <filename unknown>:0 

  at Part+.MoveNext () [0x00000] in <filename unknown>:0 

It has something to do with the part im building on (testModule)

Here is the code of the class:

public class testModule : PartModule
	{
		public int timer = 0;
		public override void OnStart(StartState state)
		{
			this.vessel.rigidbody.freezeRotation = true;
		}


		public void Update(){

			if (this.vessel == FlightGlobals.ActiveVessel) {
				if (timer <= 350) {
					Vector3d position = this.vessel.findWorldCenterOfMass();
					Vector3d eastUnit = this.vessel.mainBody.getRFrmVel(position).normalized;
					Vector3d upUnit = (position - this.vessel.mainBody.position).normalized;
					Vector3d northUnit = Vector3d.Cross(upUnit, eastUnit); //north = up cross east

					this.vessel.SetWorldVelocity((eastUnit*timer)+(upUnit*timer));

					timer++;

				}else{
					this.vessel.rigidbody.freezeRotation = false;
				}
			}
		}
	}

[nahkranoth]

I solved it. Noticed that it had to do with [this.vessel.rigidbody.freezeRotation]. After I removed it, it worked like a charm.