Navigational Directions in space

[Steel]

The word is 'plane', not 'plain'.
Anyway:
What's the point of a galactic coordinate system? Why would you use it?
Supposing you are using it, how much time are you going to spend listing decimals? "He's at somewhere within a light year radius of galactic position 0, 0, 0.00004!" - The galaxy is so big, this system isn't likely to be precise enough to be terribly useful. It'll just be clunky to use.

So what kind of OTHER coordinate system would you be using if you were to have ships travel from one part of the galaxy to the other, preferably arriving in the system they were aiming at?

This objection looks particularly stupid in light of the fact that current military grid references can be 10 digits and a GPS display gives you ~12 digits representing your position. Your coordinate system has to be precise enough for your applications, and if thats tiny in comparison to the overall scales you're working in then tough shit. Even in a local coordinate system you would need loads of figures more than is practical for a human to remember/use, so its all going to be stuffed into the computer anyway, so the number of digits you have is totally irrelevant. You cant just point at something and hope, you'll either die of starvation or old age long before reaching it.

The reinvention of the wheel here is pretty good as well. Cylindrical polar coordinates have been around for so many centuries!

[rhoenix]

I wanted to thank the author of this thread, and those who've contributed to it.

I had set this particular detail of writing scifi on the back burner until I came up with a good solution, and this thread provided an elegant and excellent solution. This was basically "let the computers do it", since they can provide a layer of abstraction between very precise and very lengthy figures, and the less mathematically-gifted beings who decide where they want to go.

[erik_t]

The Milky Way is on the order of 1e5 light years across. A 64-bit computer like my own desktop would suggest, based on the diameter of the Milky Way, a naive resolution of on the order of 10 light-hours; the orbit of Uranus/Pluto, give or take.

Why would anyone have a step between galactic-reference and planet-reference? Any system with galactic references implies FTL, and any orbits of a plant will be within a tenth of an AU anyway.

[Junghalli]

Why would anyone have a step between galactic-reference and planet-reference? Any system with galactic references implies FTL, and any orbits of a plant will be within a tenth of an AU anyway.

For establishing directions in a solar system?

[Oskuro]

I think the point of a universal system is to have a frame of reference for the more precise systems. It's like navigating a city. If you are familiar with the city, you can use directions relative to some landmark (2 streets from the stadium), if you're not familiar with the area of the city, you might navigate by street and number, but that might require checking on a street guide, wich is a bit more complex. If all fails, you can go and plug the latitude and longitude on a GPS or Google maps, but again you'll be resorting to more complex devices.

Being able to say where in the galaxy your home system is with respect to the center might be useful if you met entities that didn't know about it. But once those local points of interest are set up, navigation becomes easier if done in reference to them.

So there, it has its uses, but it wouldn't be sensible to have a starship captain bellowing "Set course for 1.5x1012AU;89º;-11º !!!"

[Cykeisme]

I don't even see a problem with the way Warhammer 40,000 and BattleTech do things.

Using "North" is fine, as long as everyone agrees upon which way is "North". In 40k, to put it very mildly, when the Imperium of Man sets the rules, all men follow those rules.
Meanwhile, IIRC, BattleTech's map is oriented such that the top is coreward of the Milky Way.

The Z-axis is, of course, still critical when you actually need to get somewhere, but in 40k their territory (most of the galaxy) is large enough and their FTL is fast enough that, when comparing locations in the "big picture" of things, it's less important.

BattleTech is a bit weird because nobody seems to consider the Z-axis in the freaking Inner Sphere. Now that doesn't make sense.

[Oskuro]

Because everyone knows the spherical shape is just an illusion, and it is just a flat disk surrounded by monsters.

[Stark]

ITT we learn gaming materials and bad fiction generally don't really address 3d navigation issues and just produce everything in a player-friendly 2d form.

WHO KNEW?

[tim31]

So there, it has its uses, but it wouldn't be sensible to have a starship captain bellowing "Set course for 1.5x1012AU;89º;-11º !!!"

Have you ever seen artillery or mortar crews at work? These are people that take precise coordinates seriously, because friendly lives may be at stake.

[Hawkwings]

Yeah, but they write down coordinates and input them into computers when they want to be accurate. Speech and hearing are so unreliable.

[Oskuro]

Have you ever seen artillery or mortar crews at work?

What's that got to do with the current discussion? Maybe you're too used to the amounts of useless technobabble spouted in Trek, but I doubt a commander has to be that precise, they just have to say "I want to be here" or "I want that destroyed" and then the navigator/gunner does the rest.

In fact, in fiction (and I guess in reality too) the captain often asks for a course to be set, leaving the calculations in the hands of the navigator (who, in a futuristic setting, will probably type the destination on a search engine, click on the resulting hyperlink, and then click OK on the "Are you sure you want to make this jump?" window that pops up. Like a GPS really.

Use of a more robust coordinate system comes in when you have to define new locations, but elsewhere, the power of google maps reigns supreme.

[Stark]

And google maps is based on... a highly detailed coordinate system, as used by artillery crews, navigators, GPS systems, etc. Thanks for playing.

It's pretty sad people can talk about wanting nice 'familiar' methods of talking about direction (even ones that basically divide the galaxy into non-intuitive wedges) AND talk about how complexity is hidden by automation. If b is true, who cares about a?

[RedImperator]

Why would anyone have a step between galactic-reference and planet-reference? Any system with galactic references implies FTL, and any orbits of a plant will be within a tenth of an AU anyway.

For establishing directions in a solar system?

That's pointless. Everything in a solar system is in motion relative to everything else.

[Beowulf]

Why would anyone have a step between galactic-reference and planet-reference? Any system with galactic references implies FTL, and any orbits of a plant will be within a tenth of an AU anyway.

For establishing directions in a solar system?

That's pointless. Everything in a solar system is in motion relative to everything else.

For system traffic control, you'd want to have a reference so that you know where everything is, and will be at given points of time. Thus you'd have a reference coordinate system, that gets automagically translated into a local ship/planet reference as necessary. Of course, it'd likely be a highly peripheral part of any story. Someone actually navigating to Mars would tell their navicomp to set course for Mars, and that'd be that.

Also, there are ways of having a object not be moving relative to sun (mostly involving solar sails, or other, effectively infinite Isp propulsion methods).

[Oskuro]

And google maps is based on... a highly detailed coordinate system, as used by artillery crews, navigators, GPS systems, etc. Thanks for playing.

Yay for Snark's lack of reading comprehension! Now go back and read the thread, this time trying to understand what we were talking about.

[Gil Hamilton]

Question: Why are we married to Cartesian coordinants for this? Why not use spherical coordinates? Astronomers already use it already and its fairly natural when it comes defining orbital movement.

For example, in a star system, define the center of the sun to be the Origin. Define the azimuth (phi) angle as starting from a line pointing directly at the center of the galaxy (which, from day to day changes an insignificant amount). The zenith pole is perpendicular to the plane of the ecliptic and points in the direction made when using the right hand rule to the standard direction of orbit in the system. Badabing. It would have to be goosed periodically with the motion of the sun around the galaxy, but on a reasonable time scale, it is reasonably immutable. It could probably be routinely corrected on the fly.

This can actually be applied to a local coordinant system used within systems specific to that system, then have a galactic coordinant system based on the same principle using a line to some landmark (like your homesystem) to define the phi angle.

Also, to make sure this system is absolute, a convention is made where the azimuth angle is phi and the elevation angle is theta. Anyone who disagrees is beat up, because that's the greek letters I learned and therefore anyone else is wrong, including the author of my P-Chem book, who reversed them.

[Junghalli]

That's pointless. Everything in a solar system is in motion relative to everything else.

I meant to say for determining position. Sorry.

[Stark]

Yay for Snark's lack of reading comprehension! Now go back and read the thread, this time trying to understand what we were talking about.

Yeah, your claims that highly detailed systems are useless because

(who, in a futuristic setting, will probably type the destination on a search engine, click on the resulting hyperlink, and then click OK on the "Are you sure you want to make this jump?" window that pops up. Like a GPS really.

which are BASED on highly detailed systems, thus highlighting Tim's point that you need to work with a detailed system for high degree of accuracy?

You even claimed you needed a better system to 'define new locations', but OTHERWISE google maps 'reigns supreme'... when it's BUILT on a 'better system', almost the exact same one Tim was talking about.

[Oskuro]

<Snark's snarky remarks>

What are you smoking and where can I get some? I began providing some ideas regarding a more universal coordinate system, but then agreed with the notion that in practical uses, those complex systems will be encapsulated, and most users won't be as aware of them because they can use future google maps to do the heavy math work for them. That doesn't rule out that a complex system is needed to plot new locations (my original point regarding the need for a system that everyone could agree upon regardless of their origin).

Of course that would have required you reading the whole thread and its evolution, but it's obviously too taxing to your vast intellect. Any other snide remarks you might want to regale us with?

[Coalition]

Question: Why are we married to Cartesian coordinants for this? Why not use spherical coordinates? Astronomers already use it already and its fairly natural when it comes defining orbital movement.

For example, in a star system, define the center of the sun to be the Origin. Define the azimuth (phi) angle as starting from a line pointing directly at the center of the galaxy (which, from day to day changes an insignificant amount). The zenith pole is perpendicular to the plane of the ecliptic and points in the direction made when using the right hand rule to the standard direction of orbit in the system. Badabing. It would have to be goosed periodically with the motion of the sun around the galaxy, but on a reasonable time scale, it is reasonably immutable. It could probably be routinely corrected on the fly.

The fun part comes when you try to apply the same coordinate system to the edge of the galaxy compared to the center. As you get further out, you need more digits for distance and for location. Admittedly you are going to have more stars at the core of the galaxy, so it could be approved via majority vote, and to hell with what the Rim thinks.

Picking a spot within 1,000 light years of the core might only require up to 4 digits for the distance, and (wild guess here) 10 digits for angle up/down and bearing. At 10,000 light years away, you need another digit for distance, and 2 more digits for angle (one each). You are 10 times the distance away, meaning if you use a base 10 navigation, you need another decimal to make sure you got the bearings correct.

But this would be good for a centralized control over the galaxy. To travel from one Rim location to another, the easiest method for the computer is to compare your start point, and see what systems are near your angles. From there, the ship plots a jump towards the core, as it can save time, knowing that there is nothing in the way. From there you have a complex jump near the core to get around that darn singularity, then you get to coordinates that allow you a straight run to your destination.

Presto - most FTL traffic will be stopping by the core, allowing it to remain the center of authority for the galaxy. Everything on the Rim mainly trades with the Core worlds in its path , then heads back. Placing military units near the Core allows for faster response times when attacking, but means that pirates with non-standard navigation systems can get around the Rim much easier (they use a few local systems for their navigation, meaning they don't have as much volume to threaten, but they can threaten their area quite well).

[Ariphaos]

Just to add some chaos to this confusion, the last I heard was that Sol was a mere 50 light years "north" of the galactic plane. Which ain't much when the thickness of the galactic arms in our galaxy are on the order of 1,000 light years.

I thought it was only twenty... anyway.

RE: "north and south". In many fields, such as electromagnetism, they use the so-called "right hand grip rule." So using this incredible slight on lefties and south hemispherians, if you curved the fingers of your right hand in the direction of galactic spin, your right hand thumb will point north.

This is what I used for a BESM game ages ago. Roughly Traveler based, spherical coordinates with Sagittarius A* as the Galactic Origin, Spinward & Trailward, Coreward & Rimward, North & South, along with Solward and Outward because anthropocentrism was not exactly dead with humans and their creations being the dominant species.

[Ariphaos]

The fun part comes when you try to apply the same coordinate system to the edge of the galaxy compared to the center. As you get further out, you need more digits for distance and for location. Admittedly you are going to have more stars at the core of the galaxy, so it could be approved via majority vote, and to hell with what the Rim thinks.

No idea why this would be an issue. I have a hard time believing we would be stuck with double precision when quad precision is already available. This is only going to be used as a galactic coordinate system anyway - local systems will reference their star or the barycenter of their pair. This provides picometer resolution out to Andromeda.

[Oskuro]

From there you have a complex jump near the core to get around that darn singularity, then you get to coordinates that allow you a straight run to your destination.

Just a nitpick here. Since due to the rotation of the Galaxy, the core is somewhat flattened over the rotation plane, it might be interesting to circumnavigate it by going above or beyond it, rather than trying to fly around it on the galactic plane.


As for the precision issue, we're talking Galaxy here, an easy system to indicate Galaxy-wide coordinates will not have the precision for star-system coordinates, so as the order of magnitude of the distances involved gets lower, we would need to switch to local coordinate systems.

I don't think different coordinate systems are incompatible at all, nor do I think there's a need for a unified coordinate system for all orders of magnitude.

[Coalition]

The fun part comes when you try to apply the same coordinate system to the edge of the galaxy compared to the center. As you get further out, you need more digits for distance and for location. Admittedly you are going to have more stars at the core of the galaxy, so it could be approved via majority vote, and to hell with what the Rim thinks.

No idea why this would be an issue. I have a hard time believing we would be stuck with double precision when quad precision is already available. This is only going to be used as a galactic coordinate system anyway - local systems will reference their star or the barycenter of their pair. This provides picometer resolution out to Andromeda.

I am figuring that whatever precision you accept at 1000 ly will require 10 times the precision at 10* the distance. Alternately, you don't need as many digits for the precision at 100 ly. Figure the coordinates would be used to form 'exit volumes' for where interstellar travel would get converted over to system travel. So you would use system coordinates until you are outside the system volume (Earth might be 2* Neptune's orbit?), then you convert to galactic coordinates. You head to the target volume (using whatever method works) then convert back over to system coordinates.

Using angles the computer can look for items with similar initial digits as the ship's current position to see what could be in the way. I.e. if you are 57.4365 left and 2.8864 up, and there is a supergiant at 57.436 and 2.88, then the computer knows that it could be in the path. No math needed calculating angles, the computer just looks up in a database. It is primarily in the form of straight lies heading towards/away from the core, but the lower processing would be useful. You just need to make sure your nav database is up to date.

It does make the Core worlds very powerful trading centers, as a world that handles trade across a 10 ly cross section (as seen from the core) would cover a trading cross section 1000 ly at a distance 10* farther away. Lots of fun bribing the politicians to choose that method.

Lord Oskuro, you are right they can just jump over the galaxy then descend, I didn't think of that.

[Oskuro]

they can just jump over the galaxy then descend

I used to do that on Freelancer internet servers when some Clan decided to blockade a trade route and demand a fee to go through. Why go around through the asteroid fields and other hazards when I can go above or under them?
(Yeah, I did forego the faster trade lanes, but both map designers and players had a tendency to forget the Z axis)