Vector3d for position

[Cryphonus]

Hi,

I wanted to get my current altitude by using the GetAltitude member function of the CelestialBody class. The argument for the funtion is a 3d vector. So how does 3d vectors are being used to express your position or any position on a planet.

PS:Please dont tell me that i can use functions that returns the double value for the altitude, I know i can and it is not suitable for what i am doing right now.

Thanks!

[Candre]

The vectors, as they appear, are just points but are called vectors so you don't have to define a new class. This assumes that these vectors are always going to be in component form.

[Cryphonus]

How do they work then, are we using a vector that starts at the origin of the planet and points to your current location on the planet? or is there some other system that i am missing?

[Tosh]

Vectors start in some arbitrary point in space, which in addition jumps randomly as the game goes. That's called 'floating origin' . So, to get vessel's position relative to planet's center, you

• get vessel's global position,
  
• get global position of current celestial body (refer to Vessel and CelestialBody classes implementations),
  
• and subtract.
  
• ah, uh, and do not store any of that 'global positions' between frames! Next jump of 'floating origin' will render them invalid! Only subtraction result will make sense then.

[Cryphonus]

Vectors start in some arbitrary point in space, which in addition jumps randomly as the game goes. That's called 'floating origin' . So, to get vessel's position relative to planet's center, you

• get vessel's global position,
  
• get global position of current celestial body (refer to Vessel and CelestialBody classes implementations),
  
• and subtract.
  
• ah, uh, and do not store any of that 'global positions' between frames! Next jump of 'floating origin' will render them invalid! Only subtraction result will make sense then.

What if I want to "predict" the altitude that is on the way of my heading? I tried adding my velocity vector to my global position vector but I dont know if it is working or not? I think Mathematically it is correct? or is it not?

[HarvesteR]

What if I want to "predict" the altitude that is on the way of my heading? I tried adding my velocity vector to my global position vector but I dont know if it is working or not? I think Mathematically it is correct? or is it not?

That's almost correct, but your velocity vector is in units/second, so what you did would give you your predicted altitude a second from "now", and a lot can happen in a second.

If you want to get your altitude at the next frame, you can do GetAltitude(position + (velocity * Time.deltaTime)).

Mind though, that this assumes no forces will act on your vessel, which is ok on low velocities, but will be pretty inaccurate in orbit, for instance. To get a more precise prediction of your position at any point in time, use the Orbit methods, like Orbit.getPositionAtUT(Planetarium.GetUniversalTime() + someTimeFromNow);

Cheers

[Cryphonus]

That's almost correct, but your velocity vector is in units/second, so what you did would give you your predicted altitude a second from "now", and a lot can happen in a second.

If you want to get your altitude at the next frame, you can do GetAltitude(position + (velocity * Time.deltaTime)).

Mind though, that this assumes no forces will act on your vessel, which is ok on low velocities, but will be pretty inaccurate in orbit, for instance. To get a more precise prediction of your position at any point in time, use the Orbit methods, like Orbit.getPositionAtUT(Planetarium.GetUniversalTime() + someTimeFromNow);

Cheers

Thanks a lot Harvester .