Celestia Forums

I am currently researching an idea, that I would like to share with you, in order to get your input:

The idea I call the "Universal Coordinate System" and the idea is to be able to represent a coordinate, with a reference to the coordinate system being used. What I mean by coordinate system, is the object that the coordinate is relative to. For example Earth, Mars, Sol, etc. The idea being that a vehicle travelling from one stella body to another can use the most convenient reference point. How this reference point is calculated is irrelavent to the solution, but what is important is the ability to translate between reference points. For example imagine a spacecraft travelling from Earth to Mars. The reference system used would be Earth, Sol and Mars.

Because stella objects are in motion, some sort of dynamic map, needs to used and time also becomes an important factor. This is because say Paris is at time 't' is no longer at the same coordinates at time 't+n', when using the sun as the reference system.

As for translating between reference systems I see using a hierarachal tree, of what I call orbital parents (what the 'orbit' is relative to). At the moment this is the most suitable I could come up with, but I am certainly
open to other solutions: A few examples:

/Universe/Milky Way/Sol/Earth
/Universe/Milky Way/Sol/Earth/Moon
/Universe/Milky Way/Sol/Mars
/Universe/Milky Way/Alpha Centurai

In theory a moving space craft could also represent its on coordinate system, in the context of the most suitable parent reference system.

Putting all this together we could record the flight of a vehicle from Earth to Mars, with the waypoints being something along the lines of the following, where COORD is "Long,Lat,Height,Time":

Ref Sys: /Universe/Milky Way/Sol/Earth
COORD 123,456,821,122344552
COORD 123,458,821,122344555
Ref Sys: /Universe/Milky Way/Sol/
COORD 123,456,821,122344558
COORD 123,458,821,122344561
Ref Sys: /Universe/Milky Way/Sol/Mars
COORD 123,456,821,122344564
COORD 123,458,821,122344566

I hope I have done a good enough job of trying to explain my idea, for
you to be able to give me your feedback.

Hello Ajmas,
The issue of coordinates has a great amount of history behind it.
Relative coordinates were explored by Einstein in the Theory
of Relativity. In his theory, time is not one value that everyone shares.
The xyz coordinates are not always defined in relation to a fixed point.

But in Celestia, relativity is not used. There is a fixed xyz point (0,0,0)
that is about 207 AU from the Sun. And time in Celestia can be stopped
or sped up. Various users use different times. Or they travel while
time is stopped.

Your idea can be developed as an alternative coordinate plan. Offsets
and rotations of coordinate systems have been done in past history. So
you can have local reference points that are just a displacement
and a rotation from the (0,0,0) point.

One issue to re-consider is the use of lat/longitude coordinates, and the
level of precision that would be needed. For example, a
triangle with an angle of 1 arc-second at one vertex will produce,
at a distance of 1 light year, an opposite side that is very large compared to a space station.

GlobeMaker wrote:One issue to re-consider is the use of lat/longitude coordinates, and the level of precision that would be needed. For example, a triangle with an angle of 1 arc-second at one vertex will produce, at a distance of 1 light year, an opposite side that is very large compared to a space station.

Hmm, not something that I had thought about, and I'll have to see how I can make that work. Maybe some sort hybrid solution would be needed? Any suggestions?

Hello Ajmas,
Do you want the coordinates to be used in Celestia?
If the answer is no, then what is the purpose of these coordinates?
If you use latitude and longitude and height, that could be useful
for short distances. For example, a calculation will now be shown
for how many nano-degrees a one meter satellite will subtend
when it is viewed from a million kilometers away.

angle = arcsin(1/1,000,000,000)
For small angles , the angle is almost equal to the arcsin of the angle.
So the angle is 1/1,000,000,000 radians.
In degrees that is 180/3,141,592,000 = 57 nano degrees
To get arc seconds multiply by 60*60
60*60*57 nano degrees = 0.0002 arc seconds

If that level of precision is good enough for your purpose,
then you need the following significant digits :
int(log base 10 (120 degrees/57 nanodegrees)) = 10

You need 10digits for lat , 10 for lon, 9 for height



Ref Sys: /Universe/Milky Way/Sol/Earth
COORD 123,456,821,122344552 old
COORD 1111111111,2222222222,666666666,122344552 new

In fact I am looking at the long term and beyond Celestia, into real space travel. If I posted here it is because I wasn't sure where else to share the idea, it could be of interest to maybe use Celestia as a reference project to do this on and I need as much feed back to evolve this solution.

Ideally I would like to make this a real project, taking in as much input possible so that it would reflect the needs of space travel, even if at this point it is in advance of a need.

Hi Ajmas,
This forum is a good one for your discussion, since non-Celestia ideas are welcome here. I am not a developer of Celestia, but The Developers read this forum every day. I am just a humble planet builder with a lot of time on my hands during this economic recession.

Ajmas said, " I am looking at the long term and beyond Celestia, into real space travel... Ideally I would like to make this a real project, taking in as much input possible so that it would reflect the needs of space travel"

During our lifetimes, real spacetravel means we will not arrive at any star system other than the Solar System. NASA has The Planetary Data System (PDS) which is using local coordinate systems. For example, The Moon has a poor coordinate system (Clementine Lunar Control Network) CLCN. NASA and the USGS are preparing a new coordinate system called the Unified Lunar Control Network 2005 (ULCN 2005).

One scientist sent me an email about this recently, since I need their data to make a Moon Globe with raised-relief:

"The main goal is to provide a consistent horizontal (latitude/longitude) coordinate system for the Moon, good to what we hope will be the few km level. However, in the process we have found that we can also recover radius information for all the points (currently 272933 points, distributed globally) that appears to be accurate at the few hundred meter level. Recent abstracts on this work are also posted at:

http://www.aas.org/publications/baas/v3 ... 05/699.htm

http://www.lpi.usra.edu/meetings/leag2005/pdf/2061.pdf

http://www.lpi.usra.edu/meetings/leag2005/pdf/2060.pdf

http://www.agu.org/meetings/fm05/waisfm05.html (search on e.g. "Archinal")

As to whether this dataset would be appropriate for making a lunar relief globe, I really can't say for sure. Our dataset will certainly be more dense than what was previously available (the Clementine lidar data) and possibly more accurate. However, I can't say whether it will be sufficient for the purposes of making a globe, particularly when it will probably depend on the scale (size of the globe). It may provide reasonable results, particularly if some smoothing/filtering is applied to the data.

Regarding when the data will be ready for release, several times this year we thought we were close to finishing our final solutions, but we've run into a number of problems mostly related to getting the relative weighting correct between our use of the Clementine image data and the original ULCN data from 1994. We believe we're close to getting a final solution now. After that we need to get a paper written and the data assembled and reviewed, probably as a USGS Open File Report that will be available on the web. As we have already demonstrated several times this year it's difficult to make an estimate for all this. Optimistically this work may be done by February, but to have it all done and released may take us into the spring.

In any case, we know that a lot of users are interested in this dataset for many obvious reasons, so we are moving along on it as quickly as we can. I will add your name to a list of people I plan to contact once the data is released.

-----
Brent A. Archinal Geodesist
Astrogeology Team
U. S. Geological Survey
2255 N. Gemini Drive
Flagstaff, AZ 86001"

End of message from Brent.

GlobeMaker resumes : So, Ajmas, read books, go to college, learn the mathematics of transformations between coordinate systems. Differential geometry is useful. Read about relative coordinates from Einstein's book "The Meaning of Relativity". Albert read a book by Tullio Levi-Civito called, "The Absolute Differential Calculus". Those mathematics propelled Alber Einstein's thought experiments toward ultimate success. And use Celestia and their nice forums. There is a "Script" capability in Celstia where you can try your customized coordinate creation. See the Scripting Forum.