# What's the difference between orientation and position?

In INS (Inertial navigation system) sensors, is there a distinction between the following?

• Orientation (heading, pitch and roll)
• Position (latitude, longitude and altitude)

Is the orientation relative to a specific axis while the position is absolute? If yes, what is the axis?

• Do you know what heading, pitch and roll are, and what latitude, longitude and altitude are...? Commented Nov 15, 2017 at 21:26
• – mins
Commented Nov 19, 2017 at 19:45

Yes there is a distinction, pitch, roll and heading are angles [unit = radian] and latitude, longitude and altitude are linear distances [unit = meter]. Together, these six parameters define the six Degrees of Freedom that define the momentary state of a rigid object with reference to the earth.

All six are defined relative to earth axes. For the linear dimensions this is clear, we just need to define a suitable zero point. For the angles:

• Pitch is the nose up/down angle relative to the gravity field of the earth.
• Roll is the wingtip up/down angle relative to the gravity field of the earth.
• Heading is the angle relative to a suitable earth reference, usually magnetic north or geographical north.

Conversion of aircraft axes into earth axes is a non-trivial matter and the cause of much confusion, for instance in questions comparing lift to weight: lift is always coupled to aircraft axes, weight to earth axes. The axes sets are defined as follows:

Aircraft axes

• Origin: Centre of Gravity of aircraft
• X-axis: in the symmetry plane of the aircraft, + = forward to the aircraft nose
• Y-axis: in the span wise direction of the aircraft, + = to the right wingtip
• Z-axis: perpendicular to the XOY-plane, + = down into the floor.

Earth axes

• Origin: Centre of Gravity at the start of the response
• X-axis: In the horizontal plane (relative to gravity), + = pointing north.
• Y-axis: Perpendicular to XOZ-plane, + = pointing east.
• Z-axis: Pointing to the centre of the earth = +

Edit

Yes navigation lat/lon is given in [degrees] - the INS sensor ultimately converts displacement into proper navigational definitions of course. But for measuring 3-D aircraft inertial effects the SI system is used, and displacement is internally treated as a linear motion, units [metres].

• I think Yaw should be the third point... Along with Pitch and Roll, it forms the 'Big-3' Rotations of an aircraft, or the 3 Degrees of Freedom... : )
– user18035
Commented Nov 15, 2017 at 7:50
• Yes the aircraft pitches, rolls and yaws - but relative to what? Commented Nov 15, 2017 at 7:58
• I think you misunderstood - I meant replacing the 'Heading' point with 'Yaw', as it sounds more complete... : )
– user18035
Commented Nov 15, 2017 at 14:57
• Down is positive Z? That seems backwards. Commented Nov 15, 2017 at 18:51
• I hate to be pedantic, but latitude and longitude, are angles not linear distances...just angles relative to the centre of the earth though the Greenwich Meridian. Commented Nov 15, 2017 at 18:56

Position is where you are; orientation is which way you're pointing (including any roll).

• Changing the word "pointing" to "facing" includes roll (in my mind at least) Commented Nov 15, 2017 at 14:57
• I've added "including roll" because I agree that's not included in "pointing" and I don't think it's implied by "facing", either. Commented Nov 15, 2017 at 15:02
• If you twist your hand while pointing, you have roll covered as well. Commented Nov 17, 2017 at 1:23

"position" is absolute. You can think of it as the x, y, z coordinates of the aircraft in the 3D space.

"orientation" is the state of the aircraft relative to its own axes:

"position" (coordinates) - https://en.wikipedia.org/wiki/Geographic_coordinate_system

• Sorry, but position is never absolute, and orientation is not a state, but a set of angles.
– bogl
Commented Nov 15, 2017 at 8:24
• @bogl An object's orientation in a specific point of time definitely describes its state. Commented Nov 15, 2017 at 8:28
• A state is a complete description of a system. The position, orientation, speed vector, and angular speed vector together describe the state of a rigid body. Orientation alone is far away from completely describing the state of a plane.
– bogl
Commented Nov 15, 2017 at 8:35
• @DeepSpace: No, it's 100% correct, because when the plane moves (pitches, rolls, yaws), its axes move too. Commented Nov 15, 2017 at 13:55
• @DeepSpace: I'm not being picky - sorry if it seems that way - but this is an important point. You can express change in the aircraft's orientation relative to its axes, but you can't usefully specify its current orientation that way - you need to relate it to some other, external reference. To clarify: can you give an example of how would you give the current orientation of an aircraft relative to its own axes? Commented Nov 15, 2017 at 14:14