How to determine xyz coordinates for an orbiting spacecraft
Posted: 23.12.2008, 19:53
Hi everyone:
I am hard at work over the holidays on a really neat add-on, that will put some of Fungun's and Reiko's models of Star Trek spacecraft in motion with respect to each other, then move them to music via a celx script and use of Celestia151-ED.exe, or by playing the music file separately. I then hope to make a youtube video of the result, to showcase to the world what Celestia can do with these magnificent add-on spacecraft. I have received Reiko and Fungun's permission, of course.
One problem that I simply cannot figure out is how to identify the x, y and z coordinates for a starting spacecraft. Let's say I place a craft in orbit above Earth via a simple ssc file. Then, I want to move that spacecraft in a particular direction, at several different speeds (it starts off slow, then picks up speed, then changes course and flies in a different direction). I understand I need to use an xyz file with multiple lines, but ... I have NO IDEA how to determine what x, y and z figures to use.
1. How do I tell what the initial x, y and z values are for that starting spacecraft? What do those values apply to (coordinate distances from Earth, or from the sun, or ...)
2. If I want to move the orbiting craft 500 meters forward to a position say 20 degrees above its starboard bow, at a speed that takes it 10 seconds to reach, how do I determine what its new x, y and z coordinates will be? (I tried using TOTI's xyz celx script, but it did not work out for me).
3. SSC files have dramatically changed since 1.4.0, with lots of new commands for positioning objects in space. There is even something called "SampledTrajectory". Has anyone written a simple to understand tutorial with examples of how to create and use these commands in ssc files, in conjunction with xyz files? (I tried understanding some reference paragraphs in the Celestia Wikibook on ssc and xyz files, but ... it was just beyond my grasp
). In particular, in studying ssc files from other add-on,s some folks will use commands with nothing in them. For example, one ssc file had this line? Sampled Orbit "" Why add it if there is nothing in it? Other ssc files use invisible CMOD models. I simply don't have the background knowledge to know what to do with them!!! 
Anyway, if anyone can shed some advice on how to determine x, y and z coordinates, and whether there is a tutorial for the new ssc commands and how to use them with xyz files, I would be very grateful. Thanks in advance to you all
for any help you can offer!
If I can work this through, I will be happy to tackle writing such a tutorial myself.
Frank
P.S. - here is a screenshot of the add-on I am working on:
Notice there are at least six moving spacecraft in this scene so far (Enterprise, Space Station, Space Dock and three shuttle pods).
I am hard at work over the holidays on a really neat add-on, that will put some of Fungun's and Reiko's models of Star Trek spacecraft in motion with respect to each other, then move them to music via a celx script and use of Celestia151-ED.exe, or by playing the music file separately. I then hope to make a youtube video of the result, to showcase to the world what Celestia can do with these magnificent add-on spacecraft. I have received Reiko and Fungun's permission, of course.
One problem that I simply cannot figure out is how to identify the x, y and z coordinates for a starting spacecraft. Let's say I place a craft in orbit above Earth via a simple ssc file. Then, I want to move that spacecraft in a particular direction, at several different speeds (it starts off slow, then picks up speed, then changes course and flies in a different direction). I understand I need to use an xyz file with multiple lines, but ... I have NO IDEA how to determine what x, y and z figures to use.
1. How do I tell what the initial x, y and z values are for that starting spacecraft? What do those values apply to (coordinate distances from Earth, or from the sun, or ...)
2. If I want to move the orbiting craft 500 meters forward to a position say 20 degrees above its starboard bow, at a speed that takes it 10 seconds to reach, how do I determine what its new x, y and z coordinates will be? (I tried using TOTI's xyz celx script, but it did not work out for me).
3. SSC files have dramatically changed since 1.4.0, with lots of new commands for positioning objects in space. There is even something called "SampledTrajectory". Has anyone written a simple to understand tutorial with examples of how to create and use these commands in ssc files, in conjunction with xyz files? (I tried understanding some reference paragraphs in the Celestia Wikibook on ssc and xyz files, but ... it was just beyond my grasp
). In particular, in studying ssc files from other add-on,s some folks will use commands with nothing in them. For example, one ssc file had this line? Sampled Orbit "" Why add it if there is nothing in it? Other ssc files use invisible CMOD models. I simply don't have the background knowledge to know what to do with them!!! Anyway, if anyone can shed some advice on how to determine x, y and z coordinates, and whether there is a tutorial for the new ssc commands and how to use them with xyz files, I would be very grateful. Thanks in advance to you all
for any help you can offer!If I can work this through, I will be happy to tackle writing such a tutorial myself.
Frank
P.S. - here is a screenshot of the add-on I am working on:
Notice there are at least six moving spacecraft in this scene so far (Enterprise, Space Station, Space Dock and three shuttle pods).