Celestia Forums

Posted: **13.12.2008, 06:19**

Hello

Yes! I hate scripts, but I love cel;//URLs

Recently I made a “script” for the topic about Cruithne and Cham asked:

Cham wrote:EDIT : Is there a way to simplify the first part of the script, to use CELX only ?

Tu parles !
The only reason why I wrote the script was because markers are not recorded within urls!

And now I have a similar problem with this little script:

Code: Select all

function CEL(source) 
   local script = celestia:createcelscript(source) 
   while script:tick() do 
      wait(0) 
   end 
end 

CEL([[
{ 
  seturl { url "cel://SyncOrbit/Sol:Earth/2008-06-21T13:21:05.18439?x=fbeWQgCMEQ&y=fg7E0iILKA&z=PMj5mKdiBg&ow=-0.573595&ox=-5.80523e-006&oy=-0.819139&oz=-3.23302e-006&select=Sol:Earth&fov=60&ts=0&ltd=0&p=0&rf=18470279&lm=2017986560&tsrc=0&ver=3
" }
}
]])

wait(2)
temps = celestia:gettime()
while (true) do
   wait(0.02)
   temps = temps +1
   celestia:settime(temps)
end

This script works ONLY with Celestia 1.6.0 because I wanted the horizontal grid to be active.
Its aim is to see the graceful Anna Lemma in the sky of the Earth.
So, the URL lets me initialize my position, time, timescale, observer’s mode and the render options with no effort. (Ctrl-C in Celestia and Ctrl-V in my script).

But I realize that it’s not a universal solution and particularly there is no way to do here some special effects. :roll:

No difficulty to set the flags and the position (here in Iceland).
The real problem for me is: how do I orient myself?
In this case facing the south and looking up with an angle = 25°. Moreover I want the ground not doing a funny angle with the horizontal. (At this place it may be ice…)

Thank you for your help. :mrgreen:

Posted: **13.12.2008, 11:19**

Jo?l,

The following commented script should help you to convert your CelURL into a nice piece of celx code.

You can use the Celx Scripting section on the Celestia Wikibook to complete it with the right time/date and renderflags definitions (grids, ...).

Code: Select all

obs = celestia:getobserver()
earth = celestia:find("Sol/Earth")

-- Define Geocentric frame of reference
e_frame = celestia:newframe("planetographic", earth)

-- Define position and orientation using cel-style URL.
u_pos = celestia:newposition("fbeWQgCMEQ", "fg7E0iILKA", "PMj5mKdiBg")
u_rot = celestia:newrotation(-0.573595, -5.80523e-006, -0.819139, -3.23302e-006)

-- Convert position and orientation from Universal to Geocentric coordinates.
e_pos = e_frame:from(u_pos)
e_rot = e_frame:from(u_rot)

obs:setposition(e_pos)
obs:setorientation(e_rot)

obs:synchronous(earth)
obs:setfov(math.rad(60))

Now, do you still hate celx ? :wink:

Posted: **13.12.2008, 15:35**

Hi Vincent,

Ha ha ha!

In my sense it is cheating because you start with values from the Url instead of the really known values that are azimuth, elevation (pitch) and roll.

I must study on it more ahead.

In fact the Wikibook is my quasi only source of knowledge for celx. But it is not so easy because if there is a comprehensible list of function, there is practically no example nor explanation on how to use difficult (for me) notions like frames of reference or rotations. Particularly I find that the description of newrotation (axis-angle) is somewhat cryptic.

But nevertheless your example is helpful and it gives me a track to follow.

I just must beware rotations because they give me vertigo!

Many thanks! :mrgreen:

Posted: **14.12.2008, 14:40**

Jo?l,

Actually, I really thought that you wanted to convert celURLs into celx code...
If you want to give observer a specific orientation using azimuth and elevation,
you may want to have a look at the celutil.lua file that's included in the Lua Edu
Tools package.

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