Setting SAS lock direction (How does VesselSAS work))

[Diazo]

Okay. I'm pretty sure this is really a question about quanterions, but for the record what I am doing is trying to set the SAS lock vector.

I am working in the VesselSAS class and there are 2 things of note in the object brower:

LockHeading(quanterion); <- Method to set the direction of the SAS lock direction
referenceHeading <-quanterion property that is the SAS 'zero'

When I do a referenceHeading.euler it returns 0,90,0 and when I set the LockHeading to a zero'd quanterion (0,0,0,0), my vessel locks heading to due east when on the KSC pad so I believe the referenceHeading.euler I can turn into a world co-ordinate vector.

I then have a world direction Vector3 with an origin at my vessel.transform.position that is the direction I want to set the SAS heading too, but I can't get this to work.

I'm pretty sure I need to get the rotation between the SAS reference position (a quanterion) and my desired heading, then apply it to a new, zero'd quanterion, then set my lock heading to that quanterion after I rotate it.

My problem is how do I get the rotation I need from the Vector 3 as a quanterion?

D.

Edited July 16, 2014 by Diazo

[NathanKell]

You should be able to construct a quaternion from a vector direction and a rotation around the axis. See what constructors the Quaternion class offers.

[Diazo]

Alright, this is absolutely stonewalling me.

Does anyone know of a mod that has worked with the VesselSAS class that I could use for pointers? A quick glance at both MechJeb and kOS's source code makes it look like they don't use it, they point the vessel with their own code.

D.

[Phooge]

Hi Diazo,

I've been looking at SAS aswell. You can create the quaternation in the direction of the vector using: quaternation.lookRotation(vector3).

You can also look at the source of Mechjeb, MechJebModuleAttitudeController.cs. It has a bit with the stock SAS. I don't exactly get what they are doing, but maby you can figure it out:)

Regards,

[Diazo]

I ended up getting this working, but it was more trial and error then anything.

https://github.com/SirDiazo/RCSLandAid/blob/master/RCSLandAid/RCSLandAid.cs#L193 is my code for reference but I ended up using:

FlightGlobals.ActiveVessel.VesselSAS.LockHeading(refQuant, true);

The true is a boolean meaning I am using Manual Lock, whatever that is. It works so I'm not arguing.

refQuant is a quaterion, but the up direction matters. I also could not figure out how the direction works.

To lock the SAS straight up for a typical rocket, refQuant is

Quaternion.LookRotation(worldUp, vslUpRef) * vslRefQuant;

where worldUp is a Vector3 from the planet's CoM through the vessel's CoM, vslUpRef is FlightGlobal.ActiveVessel.transform.up and vslRefQuant is Quaternion.Euler(90, 0, 0).

It took a lot of guess and test to reach that and I don't really get what is all means.

I was able to shortcut because using only the 90° axis angles makes things simple, but this was still a big headache to figure out.

D.

[Phooge]

After playing around with it some more today, I came up with pretty much the same solution. And I also haven't got a clue what the manual lock is:)

The mechjeb code also uses the Quaternation.Euler(90,0,0), so i gues that is the right way.

I did find a way prevent the SAS to go mad when you set it:

currentHeading = Quaternion.LookRotation(vessel.transform.up) * Quaternion.Euler(90,0,0);
targetHeading = Quaternion.LookRotation(targetVector) * Quaternion.Euler(90,0,0);

if (Quaternion.Angle(currentHeading, targetHeading) > 10)
            {
                target = Quaternion.RotateTowards(currentHeading, targetHeading, 2f); 
            }
            else
{
            target = Quaternion.LookRotation(targetHeading);
            }

part.vessel.VesselSAS.LockHeading(target, true);

Hope this makes sense.

[pixartist]

After playing around with it some more today, I came up with pretty much the same solution. And I also haven't got a clue what the manual lock is:)

The mechjeb code also uses the Quaternation.Euler(90,0,0), so i gues that is the right way.

I did find a way prevent the SAS to go mad when you set it:

currentHeading = Quaternion.LookRotation(vessel.transform.up) * Quaternion.Euler(90,0,0);
targetHeading = Quaternion.LookRotation(targetVector) * Quaternion.Euler(90,0,0);

if (Quaternion.Angle(currentHeading, targetHeading) > 10)
            {
                target = Quaternion.RotateTowards(currentHeading, targetHeading, 2f); 
            }
            else
{
            target = Quaternion.LookRotation(targetHeading);
            }

part.vessel.VesselSAS.LockHeading(target, true);

Hope this makes sense.

Hi, what kind of values does your "targetVector" take ? Are they basically navball values ?