General Question velocity vector - Is this a bug ?

[SPASE_1976]

When i switch from surface to orbit HUD the velocity vector (the circle with a cross inside ) is not at the same point , in my opinion it should.
I was thinking of posting this to the bug section but i am not sure if it's a bug

 

[Fizyk]

It's because the Earth is rotating, so the surface is moving and your velocity relative to the surface is slightly (slightly... by up to 1600 km/h on the equator) different from that relative to the center of Earth.

 

[agentgonzo]

I'd always wondered why they weren't in the same place too, but never bothered to ask. Many thanks for the reply Fizyk! Makes sense now.

 

[n122vu]

Am I mistaken or is it that in Orbit HUD mode, that indicator does not function as a velocity vector, but rather an indication of prograde direction of your orbit in relation to the reference planet?

 

[TSPenguin]

Am I mistaken or is it that in Orbit HUD mode, that indicator does not function as a velocity vector, but rather an indication of prograde direction of your orbit in relation to the reference planet?

Yes and no, because prograde is exactly your velocity vector.
Think about it...

 

[SPASE_1976]

i'm utterly confused but Fizyk's explanation sounds reasonable so i wont post it on the bug section.:hotcool:

 

[RisingFury]

i'm utterly confused but Fizyk's explanation sounds reasonable so i wont post it on the bug section.:hotcool:

Think about it in terms of two cars going different speeds, but same direction (to simplify things). Car A is driving at 50 and car B is driving at 60. Car B will overtake car A at a relative velocity of 10, while it's absolute velocity is 60.

Same applies here. Surface HUD shows velocity relative to the ground. Now, since Earth is spinning, the surface has velocity as well...
The Orbit HUD shows your absolute velocity, as if the Earth didn't spin.

 

[Andy44]

The Surface HUD is using the Planet-fixed reference frame, while the Orbit HUD is using the planet-centered inertial reference frame.

The first frame is fixed to the planet's surface and rotates with the planet, while an inertial frame is fixed to the distant starfield and remains steady while the planet rotates within it.

Kepler's Laws are only valid in an inertial frame.