How Fast Am I Going?

[Chaodiurn]

Greetings!

As it is widely known, determining your speed and your precise movement vector isn't the easiest nor clearest thing to to in E: D. Generally, the shown speed seems to apply to the direction you go into the fastest, at least if you think that you go partially into the direction you point your nose at (ends ultimately with the movement vector, which has to be guessed). Add thrust into a direction = change movement vector as long into that direction, until it equals your desired way to go to. There, FAoff in a nutshell.

But be that as it may. The whole gets even more confusing when there are two measurements for velocity, each showing different values! The one doesn't change (normal speed-o'-meter), the other changes as you change direction (save-to-exit bar). I totally ignore that it only happens in magical super cruise, where you defy everything that weird German said somewhen.

I must ask thus: how fast am I really going? And where? And why?

 

[Deleted member 38366]

--- Deleted ---

 

[Jmanis]

Frontier: Elite 2 and Frontier: First Encounters used to have two reticles. One was the direction you were facing, and the other was direction of travel. Your speed was in the direction of travel. That reticle doesn't exist in Elite: Dangerous, so I've just learned to judge it, but it would be handy to have it back.

 

[Equinoxe]

Could the other indicator be lateral speed in relation to your target?

 

[Adept Geraden]

Because the thing you have targeted is also moving in space. Your absolute velocity is 30Km/s. Your target is moving towards you at 21Km/s, so your velocity relative to the target is 30 + 21 = 51Km/s. Pretty neat actually.

 

[CakeEngine]

Because the thing you have targeted is also moving in space. Your absolute velocity is 30Km/s. Your target is moving towards you at 21Km/s, so your velocity relative to the target is 30 + 21 = 51Km/s. Pretty neat actually.

^This. And it should also answer your Question about:

[...]The one doesn't change (normal speed-o'-meter), the other changes as you change direction[...]

Think of your ship and your target as Vectors facing each other and it should become more clear, why the relative velocity indicator changes it's value while you're pointing your 30 km/s -Arrow in a different direction.

 

[Chaodiurn]

Because the thing you have targeted is also moving in space. Your absolute velocity is 30Km/s. Your target is moving towards you at 21Km/s, so your velocity relative to the target is 30 + 21 = 51Km/s. Pretty neat actually.

As awesome as it sounds, that would make for a very weird calculation. I returned and tried to get into different angles that allow me to stay at 48.0 km/s. See yourself:





The slowest I achieved was to turn somewhere into the nothingness:



While turning straight away from it got me faster again:



I mean... huh?!
Edit: Could it be the whole thing just can't handle negative speeds? So, if I'm departing on a certain speed, it still shows that as closing in? I tried (bow to my Gimp skills!) to get some visual display of angles down. On both screenshots I fly with the same speed (43.3 km/s) according to the save-to-exit screen. Admittedly it's rough work being done and could be done more precise. Still, I hope it helps to show why I doubt the system.

 

[CakeEngine]

While turning straight away from it got me faster again:
[...]
I mean... huh?!
Edit: Could it be the whole thing just can't handle negative speeds? So, if I'm departing on a certain speed, it still shows that as closing in?

Maybe it's because there is no such thing as "negative" speed at all. You're just moving in a different direction. If you increase your throttle a bit, you may see the relative speed meter go up, because your relative speed increases while you accelerate.
...maybe a picture will help



It may be, that your targets relative speed to you is just about 7,9 km/s towards you, while you veer away from it with 30 km/s, leaving you with an overall relative speed of 22,1 km/s.

Your slowest speed encounter, where you were headed to "something into nothingness", might have been you pointing somewhere parallel to your targets actuall vector.
Hope that helps a bit

 

[Jason S]

And now time for ludicrous speed.

 

[Chaodiurn]

Maybe it's because there is no such thing as "negative" speed at all. You're just moving in a different direction. If you increase your throttle a bit, you may see the relative speed meter go up, because your relative speed increases while you accelerate.
...maybe a picture will help

<snip>

It may be, that your targets relative speed to you is just about 7,9 km/s towards you, while you veer away from it with 30 km/s, leaving you with an overall relative speed of 22,1 km/s.

Your slowest speed encounter, where you were headed to "something into nothingness", might have been you pointing somewhere parallel to your targets actuall vector.
Hope that helps a bit

Isn't relative speed where negative speeds come into play in the first place? Let's say I'm moving in on the target that's orbiting the planet clockwise. To do so, I engage the station by flying anti-clockwise around the planet. So the target's speed adds to my 30km/s: 30 km/s + 7,9 km/s = 37,9 km/s. If I, however, fly away from the target, I'm "closing in" at -30 km/s. Since the target's speed still adds to mine to calculate the relative speed, I'm moving at: -30 km/s - 7.9 km/s = -22.1 km/s.

If we say that speed always is positive and it's just it's vector that changes (physicians may do so), it would still imply, that I'm going towards the target, wouldn't it? That's why you need to roughly point your nose towards to target to engage target lock for dropout. My relative speed should be equal to my true speed when flying in from an orthogonal angle and equal zero when flying parallel towards the target's speed with matched velocity.

I imagine the whole problem like a car crash: when two cars crash, you cannot ignore the movement vectors. If a car that goes 120 km/h crashes into a car that comes its way with 110 km/h that's way more fatal than a car crashing on 120 km/h crashing into the car driving before it with 110 km/h. The "impact speed" changes from 220 km/h to 10 km/h!

Is the heat slowly melting my brain? It seems too possible. Because my brain just tried to add the movement vectors of the target and the ship in the graphic together, to calculate the new direction. In summer everything's bad! Give me winter back! I want snow and ice. (Thanks for that by the way!)

 

[CakeEngine]

Is the heat slowly melting my brain? It seems too possible. Because my brain just tried to add the movement vectors of the target and the ship in the graphic together, to calculate the new direction. In summer everything's bad! Give me winter back! I want snow and ice. (Thanks for that by the way!)

No no, you're absolutely right in your conclusions, despite the justified need for snowflakes calmly melt on your forehead while you're facing a mild winter breeze...
...wait, where was I?
Oh, yes. See, it's just like you said before. You simply don't apply a prefix to speed. While the assumption that a minus value of speed means that you are going backwards, MIGHT work out in a 2-dimensional system, it gets weird if you try to transfer this approach on to three or more dimensions, eventually leading to false calculations.
While you are correct, that your target chases you with 7,9 km/s and therefore reduces your speed relative to it to 22,1 km/s , mathematically it doesn't work how you descriped it.

I'm moving at: -30 km/s - 7.9 km/s = -22.1 km/s.

Because, -30 -7,9 = -37,9 and not -22,1
And still you're moving with the speed of 30 km/s. Your not going backwards, are you? And if you could hit the thrust reverser in order to fly backwards, you wouldn't get a negative speed, would you? You still fly at a positive speed. May the acceleration be negative, you still got a positive speed until it gets down to zero and then back up again. Just in the opposite direction this time.

May i assume, that the whole "closing in/getting away" is what threw you of in the first place?
Maybe there lies the rub. In that case, it's a matter of your point of reference.
If you set your target as reference point, you're getting away, while the target stands still.
If you set an imaginary stationary camera limbet outside your ship as point of reference, you're getting away, while your target closes in.
From Sagittarius A*s point of view, you and your target both are crazy; just running around in weird circles.

Don't take the relative speed indicator as more as it is. It doesn't indicate if you are getting nearer to your target or further away. It just shows the speed difference between you both.

btw. +rep for the Asterix reference in your sig.

 

[Schmack]

I can't read French, but I can take a stab at it. You're close to a big yellow ring.

 

[Chaodiurn]

No no, you're absolutely right in your conclusions, despite the justified need for snowflakes calmly melt on your forehead while you're facing a mild winter breeze...
[...]
Because, -30 -7,9 = -37,9 and not -22,1
And still you're moving with the speed of 30 km/s. Your not going backwards, are you? And if you could hit the thrust reverser in order to fly backwards, you wouldn't get a negative speed, would you? You still fly at a positive speed. May the acceleration be negative, you still got a positive speed until it gets down to zero and then back up again. Just in the opposite direction this time.

May i assume, that the whole "closing in/getting away" is what threw you of in the first place?
[...]
From Sagittarius A*s point of view, you and your target both are crazy; just running around in weird circles.

Don't take the relative speed indicator as more as it is. It doesn't indicate if you are getting nearer to your target or further away. It just shows the speed difference between you both.

btw. +rep for the Asterix reference in your sig.

Took me a while to realise this reply was longer than two lines. So, eh... maths! Utterly, theoretical maths! If I am flying away from a station parallel to its velocity vector (better than movement vector, huh), I should be perceived slower from the station, against flying orthogonal to it. With that, I should be perceived faster from the station when heading towards it parallel to its velocity vector, against flying orthogonal to it. Right?

So, staying with the source of confusion, relative directions, and keeping the prefixes, we should get for heading towards a station:
Velocity value ship + velocity value target = relative velocity value <- this is what should generally be right for everything involved

...while for flying away from the target the following should apply by my logic:

-Velocity value ship + velocity value target = relative velocity <- This was my thought in the post above. The minus was a typo.

Alternative it would be possible to use (if one said only relative velocities may be negative):

velocity value ship - velocity value target = -relative velocity <- I probably threw that idea in halfway typing, resulting in a weird mix.

You probably notice that this is the same as above multiplied by -1. It only really breaks with the rule, that the velocities always behave additive. It just seems weird to me that my relative velocity, when moving into the same or a similar direction as my target, is rising. To me, -37.9 km/s, while the number is smaller, is faster than -22.1 km/s, because, in the end, velocity vectors come without prefixes.

I can see how this leads to problems. When are the angles between the velocity vectors so, that something moves away from the other? Still. Relative velocities, to me, seem to indicate how fast something is perceived by something it moves in relation to (thus relative velocity). That, indeed, is the ultimate source of my confusion. As soon as you are perceived by something, you are either moving in our out, at different angles and speeds, but it's either coming closer or is leaving. Alternatively, if the relative velocity equals zero (another thing that irritates me, since only positive values involved in an addition may never reach 0, what definitely is possible), it stands still. "Doesn't indicate if you are getting nearer to your target or further away" thus is exactly the opposite as of what I understand by it!
Edit: I'm NOT trying to set target = reference system. I think

Sagittarius A*, while providing the gravitational force that influences both, is not inbound in the equation and thus has to have no opinion. Although I just perfectly can see its face while watching us going crazy on Powerplay...



Then, when someone visits, it swiftly goes:





And yes, the signature! Asterix is just awesome.

 

[Brimstone]

Why do people say kilometers, but then million meters rather than megameters?

 

[Chaodiurn]

Why do people say kilometers, but then million meters rather than megameters?

Because it's easier to say. "thousandmeters," seriously? Makes you sound like an angry German. It's the same reason why Frenchmen say "de la" but hate the sound of "de le" that much that they make it "du" instead. And since we deal with mega units that rarely in daily live, nobody knows what a mega is. I recently overheard, and this is no joke, asking a guy in the train his comrades "What is more? A mega or a million? Mega is more, right?"

 

[CakeEngine]

Ok, i'm really sorry Chaodiurn.

I had a post for you on which i worked for the last one and a half hour, clarifying everything (sentence by sentence) in every depth and detail.
But somehow I managed to close the tab, leaving me with nothing more than blank space and some marks on my forehead from smashing my head against my table.

So, as much as i regret it, but at this point, there is nothing else but for me to somehow sum it up.
Ahem..
"All of what you said is basically correct. But in the end, there is just no prefix to the value of a velocity. Because it is it's "value" (or in terms of vectors, it's "length"). Your former prefix however, ends up beeing the velocitiys direction."

Again. Sorry for this very very very short answer.

 

[Captain N]

Pretty sure a speed cannot be negative, as correctly it would be defined as the length (or magnitude) of a velocity, which is a vector. A vector cannot have a negative magnitude.

 

[Chaodiurn]

Ok, i'm really sorry Chaodiurn.

I had a post for you on which i worked for the last one and a half hour, clarifying everything (sentence by sentence) in every depth and detail.
But somehow I managed to close the tab, leaving me with nothing more than blank space and some marks on my forehead from smashing my head against my table.

So, as much as i regret it, but at this point, there is nothing else but for me to somehow sum it up.
Ahem..
"All of what you said is basically correct. But in the end, there is just no prefix to the value of a velocity. Because it is it's "value" (or in terms of vectors, it's "length"). Your former prefix however, ends up beeing the velocitiys direction."

Again. Sorry for this very very very short answer.

Aww, I'm sorry to hear that.
All my thanks for that gigantic effort! Having something just vanish that one has worked for that long really is a bad thing to happen. I always find it next to surreal when a person invests that much time into something just because of me. I once intentionally misclicked to see if the box keeps the text (like opening it from history and the like). When I saw it didn't, I got way more carefully while posting!

I will live with that explanation for now, and perhaps hit up some openMIT vids or something on the topic later on.

Thank you very much again for the (sadly lost) effort still! I'm sure it was something awesome!

And to lighten you up a very bad joke! If I fly at 1c every second, does that turn my velocity into a length?