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I have a list of positions (X [NM], Y[NM], Z[NM]) of an aircraft. Every coordinate is given every 1 second.

I calculate the speed [knots] between two consecutive coordinates in the following way:

$S_{i+1}=\frac{\sqrt{(X_{i+1}-X_{i})^2 + (Y_{i+1}-Y_{i})^2 + (Z_{i+1}-Z_{i})^2}}{1s}3600\frac{s}{h}$

It's basically space over time.

Does this 3D speed have a specific name?

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    $\begingroup$ That's a trippy question :) $\endgroup$ – Koyovis Nov 24 '17 at 13:49
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    $\begingroup$ I dunno what you are trying to solve for there. Yeah, technically it would solve for velocity, but I don’t know where such a calculation would be used in aviation. $\endgroup$ – Carlo Felicione Nov 24 '17 at 14:09
  • $\begingroup$ I don't want to try to solve anything... I just wonder if such speed has a specific name... it seems to me strange that there are definitions for ground speed, airspeed and so on but no definition for what I consider the most intuitive and basic definition an aircraft can have... $\endgroup$ – Federico Gentile Nov 24 '17 at 15:26
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    $\begingroup$ How is this not instantaneous ground speed ? $\endgroup$ – Jeffrey Nov 24 '17 at 16:26
  • $\begingroup$ Ground speed does not have the z-axis $\endgroup$ – Koyovis Nov 25 '17 at 11:00
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It describes what the velocity vector of the aircraft centre of gravity is in relation to the surface of the earth. Ground speed is the 2-D projection of your speed on the ground, climb speed is the vertical component.

Both ground speed and climb speed are very useful parameters as such: ground speed to figure out when the aircraft arrives, climb speed to adjust engine settings etc for reaching cruise altitude with a minimum amount of fuel used. The 3-D vector sum of the two has little practical use, that is probably why it has no separate name as far as I know.

The integrated signal is of more use: what is the position in 3D of the centre of gravity of the aircraft relative to earth? Pretty useful for navigation.

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