Standard maneuvering coordinate system?

[Enoki]

Again with an esoteric question: Does Traveller have some sort of standard method of determing the direction of movement of a ship in terms of its coordinates like is used by aircraft or ships on Earth? Or can one be recommended. It sometimes is nice to be able to give players this sort of a thing as a problem to solve. It is sort of a "Let's see some navigation and piloting skills since your character has them...." sort of thing. :devil:

 

[Matt123]

Spinward, Trailing, Careward, Rimward & errr Up & Down (normally ignored in our 2d Traveller universe)...

Dunno if that fits your purpose?

 

[Icosahedron]

Directions on Earth are related to Magnetic North. I could see in space that directions might be related to a gravitational 'pole' - at orbital range that would probably be a line passing through the planet centre, beyond orbit, the pole might switch to the direction of the local primary sun, and if you venture significantly beyond the system, it might switch to the galactic centre.
Of course, space co-ordinate systems would have to be three-dimensional.

 

[Matt123]

Maybe measured from the planet/star in degrees, with coreward being 0 degrees?

Is there an easy or logical way to measure or define the horizontal plane?

Perhaps for example resulting in a position from Regina of;
110 degrees, 5000km, -2000Km.

Looking 'down'
....................C..................
........................................
........................................
........................................
.....................R.................
........................................
................................^..... (5000km out from Regina along the 110 degree angle)
.......................................

Looking 'coreward'
.......................................
.......................................
....................................... (+2000km)
.......................................
.....................R................ (0KM based on the flat plane of the system or galaxy?)
.......................................
.................................o.... (-2000km)
.......................................

Might work? The area covered by the degree arc might be quite large though.

 

[Spinward Scout]

Careward

And when you get real close it's an Intensive Careward.

I think you meant Coreward.

 

[McPerth]

I think the easiest refference to have on a system is the central sun (or the one the planet closer to you orbits in cas of multiple star systems). From this refference point, a degrees (or radians) and distance system could be used to mark the position.

The zero line Greenwich meridian equivalent) could be the line from star to main world (this would have some problems on Asteroid Belt main worlds), or the direction of some refference (galaxy core, etc), over the plane of rotation of the planets.

This same plane of rotation would be the zero line for the third dimension, applying the Right Hand Rule to give positive or negative.

In starless hexes, things get a little more complex...

 

[far-trader]

I'm all but certain I've seen a Ring/Ray coordinate system for Traveller somewhere. MT Referee's Companion?

 

[navanod]

Hmmm.... The Traveller Book, I believe. Don't have mine handy tho.

 

[far-trader]

Right you are navanod, Library Data entry actually (from Supplement of the same):

Also on the Traveller Wikia:

http://traveller.wikia.com/wiki/Astrography

 

[McPerth]

Oh, I undertood Enoki asked about opperations in system and in normal space. If I was wrong on that, my earlier post (and the rest of this one) lose all sense.

The Ring/ray system positions a star (and so a system) into the galactic map, but is abolutely useless into system, as would be to sent a mayday.

The system I sugested above would be just for that:

'Mayday, here's Imperial Trader Star Ruin calling for help. Maneover Dive malfunction. Our position is +30º 26' 33"/+2º 15' 24", 2.3 AU. Moving direction -60º at 5 kk/hour speed'

As you see, the system name is not even given, asi it is irrellevant. If you have to wait for outsystem help, then you're lost anyway.

 

[Enoki]

I think the easiest refference to have on a system is the central sun (or the one the planet closer to you orbits in cas of multiple star systems). From this refference point, a degrees (or radians) and distance system could be used to mark the position.

The zero line Greenwich meridian equivalent) could be the line from star to main world (this would have some problems on Asteroid Belt main worlds), or the direction of some refference (galaxy core, etc), over the plane of rotation of the planets.

This same plane of rotation would be the zero line for the third dimension, applying the Right Hand Rule to give positive or negative.

In starless hexes, things get a little more complex...

This is sort of how I figured it to be. You use the rotational axis of the sun as the "Y" axis going from 0 to 180 degrees. The "X" axis is simply taken as 90 degrees to the Y axis with zero taken as referenced to the primary planet of the system. You then describe a triangle from these to the position of the ship. The ship references this tangent line as its relative 0 position and calculates a second triangle to the point it wants to move relative to its own current position. The resulting tangent line (hypotneuse) is the relative course from current location. So you would give the course as 0-360 degrees on an x bearing and 0 - 180 degrees on a y bearing. Or something like "Course 120 by 92"

 

[D. Foxx]

The Star Trek: The Next Generation Technical Manual lists several "Flight Information Input" methedologies, two are listed below:

"relative bearing" which is based off of your crafts orientation to an object. Dead ahead is 0 degress with increasing values going clockwise (azimuth angles) from a view looking down at your ship, and increasing values going counterclockwise (elevation angles) from a view looking at the right side of your ship. The object is bearing 090, mark 15 equates to 90 degress to your right and 15 degress up.

"absolute heading" is similar to relative bearing except you always use the center of the galaxy as you orientation point. heading 090, mark 15 would mean that based on your flight path, the center of the galaxy is 90 degress to your right and 15 degrees up.

 

[McPerth]

But using the center of the galaxy for you position into a system (what you need when sending a mayday or want to point the position if an intruder fleet) is not an option, as (from this reference) either you use 10 or 12 digit numbers (at least, probably more) or the area pointed will englobe all the system.

That's why I gave as reference the main star of a system, as (at least in traveller, Startreck, as uses warp drives moves by empty space too) it would be the only places where you must give your (or other's) position.

While in normal space, the only position you ever need to give is into a system, as, in traveller, empty hexes are rarely travelled, and usually out of contact from everybody anyway.

 

[whartung]

Yea I was curious what the standard measurement was for in system travel. I think most navigation would be relative to the system primary in some way, with perhaps a "constant" of "galactic north" (perhaps coreward) where the degrees start and 0. Then, are do the degrees advanced in the direction of the orbits? I don't know for sure off the bat, but don't we transit around the Sun counter-clockwise?

The problem is how do we determine "north". We, here, are fortunate to have a magnetic field to point to "0". But that's not the same as in space. Now, something could be "agreed" upon, each system may have a "stable enough" star to use as a reference, and from there, astrographers can detect the core, and say "coreward is P degrees by R degrees off of Star X" just to give some sense of reference in the system. But transiting out of Jump space, how do you pick that reference star out of the zillions of others when you may not know what your reference is coming in.

Perhaps the astrogation computers can take some quick snapshots of the sky around the ship looking for patterns that it "knows" should be there for that system (constellation patterns, etc.). Once it find the Big Dipper, so to speak, it can figure everything else out.

This just brings about the issues of deep space navigation in general. I always thought that for "short jumps" (few parsecs) that perhaps deep space objects, notably Pulsars, could be used as beacons. These are ideally reasonably stable for several thousand year. It would be curious to discover a Pulsar that is so close to the end of its life that its signature changes as you get closer and closer to it. Normally a few hundred years don't matter. But who knows how a Pulsar dies.

 

[McPerth]

That's just why I said some point must be used as reference.

I think it may be the main star, as I posted before. Though that's not a stable point (as you said), due to the rotation arround the star, that's really not necessary, as any two reference points may work as well (and we agree one of them should be the main star, for sake of simplicity), and the main world is something easy to pick and use as reference (with the possible mentioned exception of asteroid belts, but there you may use the main starport). Do not forget also that it would probably be the most travelled place in the system, so easing even more the references.

It could also be something so far as being nearly equal for all systems (as may be galactic core) or even just a beacon put somewhere in the system just for that pourpose, not caring about if in some system that means the direction of the galactic core and in another the direction is perpendicular to it.

The main concept (IMHO) is that the exact points and directions need only work for that specific star system, while the method to give refferences and positions must work for any star system, just as a magnetic compas may be useful in any planet (as long as it has a magnetic north), but may well not point the same direction (relative to the galaxy) in all planets.

 

[Enoki]

Yea I was curious what the standard measurement was for in system travel. I think most navigation would be relative to the system primary in some way, with perhaps a "constant" of "galactic north" (perhaps coreward) where the degrees start and 0. Then, are do the degrees advanced in the direction of the orbits? I don't know for sure off the bat, but don't we transit around the Sun counter-clockwise?

The problem is how do we determine "north". We, here, are fortunate to have a magnetic field to point to "0". But that's not the same as in space. Now, something could be "agreed" upon, each system may have a "stable enough" star to use as a reference, and from there, astrographers can detect the core, and say "coreward is P degrees by R degrees off of Star X" just to give some sense of reference in the system. But transiting out of Jump space, how do you pick that reference star out of the zillions of others when you may not know what your reference is coming in.

Perhaps the astrogation computers can take some quick snapshots of the sky around the ship looking for patterns that it "knows" should be there for that system (constellation patterns, etc.). Once it find the Big Dipper, so to speak, it can figure everything else out.

This just brings about the issues of deep space navigation in general. I always thought that for "short jumps" (few parsecs) that perhaps deep space objects, notably Pulsars, could be used as beacons. These are ideally reasonably stable for several thousand year. It would be curious to discover a Pulsar that is so close to the end of its life that its signature changes as you get closer and closer to it. Normally a few hundred years don't matter. But who knows how a Pulsar dies.

I'd define "north" and "south" as a galactic one by convention. As for movement of the planets and sun in a system this would be accounted for as in naval navigation as "set and drift." As in ded reckoning, you adjust for wind, currents and, such here you compensate for the motion of the sun, planets and, I would presume solar wind. Of course, in terms of Traveller you needn't be so precise and just the unadjusted absolute and relative courses need be applied. All of this applying to maneuver at slower-than-light travel.

For this problem you don't need a reference beyond the system you are in as it presents the only points you are navigating to. What another system is doing is only relevant when you jump.

 

[Ben W Bell]

In MTU when in system if I'm trying to determine points in space I base the coordinate system off a base axis line from the centre of the star on a line through the centre of the mainworld. 0 is the stars centre and the 0 line axis the line through the mainworld. Everything can the be determined from that for coordinates within the system. Obviously the coordinates change as the mainworld orbits the star, but it's nothing even the simplest navigational and location computer cant cope with. Relation to the rest of the galaxy isn't relevant in this frame.

When doing jump coordinates its bases in galactic position relative to the galactic core and trailing/spinward coordinates.

 

[Icosahedron]

I thought he was asking about a bearing (NbyNW) the ship might move on. If the question was about locating a stranded ship, surely the way to go would be a finer scale version of the galactic map? I'm picturing the Parsec-hex being divided up into smaller hexes in much the same way as gaming maps do. Since most starsystems have a plane, you could even get away with a 2D map. Or, a similar hex-of-hexes map centred on the star, with a diameter equal to the system diameter, then break this down into smaller hexes if needed. The hexes would always be aligned with the galactic map.

 

[Matt123]

I'm a little surprised the consensus seems to be on using the direction to the main world from the sun as a 0 degree reference. And I'm not sure I understand the logic for dismissing using the galactic core, although using some significant star/pulsar males sense, especially if it can apply across a political entity (from the pov of setting navigational standards).

I like the idea of setting the system plane according to the primary stars equator. I assume its not too difficult to determine when first arriving in system?

Thinking on it, I guess ideally both your primary co-ordinates ought to be either system based or external/galactic based. So ether 0 degrees is the line from the sun to main world and the suns equator determines the system plane, or the galactic center/pick a pulsar is 0 degrees and the plane is the galactic plane.

The other consideration is whether in-system travel should use different reference points to jump travel.

And a final thought, when measuring your location in degrees relative to the sun, while on approach to earth, to how many decimal places must you measure to get a +/- 10m3 accuracy?

 

[McPerth]

I'm a little surprised the consensus seems to be on using the direction to the main world from the sun as a 0 degree reference. And I'm not sure I understand the logic for dismissing using the galactic core, although using some significant star/pulsar males sense, especially if it can apply across a political entity (from the pov of setting navigational standards).

I like the idea of setting the system plane according to the primary stars equator. I assume its not too difficult to determine when first arriving in system?

Thinking on it, I guess ideally both your primary co-ordinates ought to be either system based or external/galactic based. So ether 0 degrees is the line from the sun to main world and the suns equator determines the system plane, or the galactic center/pick a pulsar is 0 degrees and the plane is the galactic plane.

I suggested to use the line form the main star to the primary world as reference (0 line) because it would be (IMHO) the easiest reference to pick when you enter a system, even though it rotates constantly arround the star.

Anyway, as all bodies in a system rotate arround the star, the position of any body will be changing at every moment, so I think no more complexity is added jsut because the 0 line rotates too (even it's a little less complex, as the main world will be in a constant (relative) position).

About the third dimension, you seem to put the 0 at the main star's equator (or at least so I understand), while I suggested the rotatory plain of the planets (which, AFAIK is more or less the same for all the planets, unless there's a captured one). I'm not sure if stars have also axial tilt in this sense...

If the plane for all the planets is not the same (or there are significant variation on it), I guess the main world should be used as reference too, for the same reasons given above.

The other consideration is whether in-system travel should use different reference points to jump travel.

Why would that be needed?

As I understand jump (I may well be wrong, off course), the jump points depend on gravitatory fields, and that's why they change all time and must be calculated for every jump. If so, and as the most used ones are the ones arround the main world (IMHO), this reference method would work quite well.

And I insist any reference method you use, all the positions in the system (system bodies, jump points, etc) will be constantly changing sue to the movement of all bodies in their orbits arround the star.

And a final thought, when measuring your location in degrees relative to the sun, while on approach to earth, to how many decimal places must you measure to get a +/- 10m3 accuracy?

I guess quite a lot...

But why do you need such accuracy? IMHO sensors would make quite less accuracy acceptable.

And even if needed (let's say jump points need it, and they are not detectable with sensors), I guess computers as represented in TU will be able to cope with as many decimals as needed.

EDIT: remember in my first post in this thread I also pointed the possibility the position could be expressed in radians, instead of degrees (as most TU uses SI units). If so, even more decimals would be used in any calculations, and most would iclude the number pi on them.END EDIT