Celx script that displays RA/Dec for observer

[ElChristou]

Would be nice to have this integrated in the default HUD (perhaps next to the FOV)... or, what about adding it to the lua tools? (with a checkbox)

[Vincent]

I edited the script to translate it in French, but the UTF8 encoding is really a pain in the butt. Each time I open the file, I'm getting weird characters and have to change them. At least, now it's working.

That's why an option to print UTF-8 chars in celx scripting would be quite useful...

Would be nice to have this integrated in the default HUD (perhaps next to the FOV)... or, what about adding it to the lua tools? (with a checkbox)

And what about giving the possibility to switch between different displays: observer's position/selection's position in geocentric/topocentric coordinates... ?
In the Lua Tools, this could be done via the config file - are there situations which would require displaying both the observer's and the selection's position?.
And for the default HUD, these options could be set via the GUI...

[Vincent]

Vincent,

Any idea what's causing this problem? Is it a bug in Lua or the Celestia print functions? It seems unlikely that there's a problem in Lua, yet Celestia routinely uses the degree symbol in strings that don't originate form scripts.

--Chris

Chris,

Displaying UTF-8 chars, like the degree symbol, works correctly in cel scripting
using their hexadecimal code, e.g., "\u00B0" for the degree symbol:

Code: Select all

{
print { origin "left"  row 1  column 1  duration 6 text "\u00B0" }
wait { duration 6 }
}

But this doesn't work in celx scripts. The following celx command displays 'u00B0'

Code: Select all

celestia:print("\u00B0")

I also tried with:

Code: Select all

celestia:print("\\u00B0")

but it doesn't work either.

One reason for this problem might be that '\' is used as escape sequence in Lua...

[Machete]

I'm interested in modifying this script to display RA and DEC of the *observed* direction. I'm new to celestia scripting, could someone give me a hint in order to do it?

edit:


I changed

Code: Select all

local rot = earth:getposition():orientationto(obs:getposition(), LOOK) * base_rot

for

Code: Select all


local rot = obs:getorientation()

I assume I'm doing something very wrong, since I point to Sirius (Right ascension 06h 45m 08.9173s Declination ?16° 42? 58.017'' ) and I get RA 6h 56m 20s and dec -39d 36' 19''.

[Vincent]

I'm interested in modifying this script to display RA and DEC of the *observed* direction. I'm new to celestia scripting, could someone give me a hint in order to do it?

edit:

I changed

Code: Select all

local rot = earth:getposition():orientationto(obs:getposition(), LOOK) * base_rot

for

Code: Select all


local rot = obs:getorientation()

I assume I'm doing something very wrong, since I point to Sirius (Right ascension 06h 45m 08.9173s Declination ?16° 42? 58.017'' ) and I get RA 6h 56m 20s and dec -39d 36' 19''.

You're on the right track. The following code should do what you want:

Code: Select all

   local base_rot = celestia:newrotation(celestia:newvector(1, 0, 0), -J2000Obliquity)
   local rot = obs:getorientation() * base_rot

One important thing to keep in mind is that you'll get correct values for RA/Dec exclusively when the observer is in the neighbourhood of the Earth.

[Machete]

Thank you, that worked like a charm

[Machete]

I'm trying now to display the quaternion of the observed point, like the quaternion a spacecraft would use. I'm a bit confused about the coordinate system here.

From what I understand, "rot" is a rotation from vector LOOK ==(0,0,-1) to the observation vector. How could I get a quaternion that can transform the vector that points to the vernal equinox (RA 0 DEC 0) into the observation vector? I would then use this quaternion to display it, as well as the euler angles generated with it.

These are the "monstruosities" I am currently making with Vincent's script. When I execute this, it looks like the origin for the euler angles is in 18h, 0 degrees.

Code: Select all

-- Return current RA, Dec for observer:
getRADec = function (obs)
   local base_rot = celestia:newrotation(celestia:newvector(1, 0, 0), -J2000Obliquity)
   local rot = obs:getorientation() * base_rot
   
   local look = rot:transform(LOOK):normalize()
   local r, theta, phi = xyz2rtp(look.x, look.z, look.y)
   local phi = math.mod(720 - math.deg(phi), 360)
   local theta = math.deg(theta)
   if theta > 0 then
      theta = 90 - theta
   else
      theta = (-90 - theta)
   end
   return phi, theta, rot, look.x, look.y, look.z
end


quat2euler =   function(qtrn)
   local   qw = qtrn.w
   local   qx = qtrn.x
   local   qy = qtrn.y
   local   qz = qtrn.z
   local   phi = math.atan (2*(qy*qw+qx*qz)/(1-2*(qy^2*qz^2)))
   local   theta= math.asin(2*(qx*qw-qz*qw))
   local   psi= math.atan2(2*(qx*qw+qy*qz),(1-2*(qx^2+qz^2)))
   
   
   return phi, theta, psi
end

while true do
   obs = celestia:getobserver()
   obsR = getR(obs)
   obsRA, obsDec, quat, xobs, yobs, zobs = getRADec(obs)
   roll, pitch, yaw = quat2euler(quat)
   celestia:print(obsR..' '..obsRA..' '..obsDec)
   if obsR >= 0 then
      -- Display geocentric coordinates for observer:
      obsRStr = km2Unit(obsR)
      obsRAStr = deg2hms(obsRA)
      obsDecStr = deg2dms(obsDec)
      celestia:print("\nRA: "..obsRAStr.."\nDec: "..obsDecStr.."\nq0: "..quat.w.."\nq1: "..quat.x.."\nq2: "..quat.y.."\nq3: "..quat.z.."\nroll: "..roll.."\npitch: "..pitch.."\nyaw: "..yaw.."\nx: "..xobs.."\ny: "..yobs.."\nz: "..zobs, 1, -1, -1, 1, 20)
    
   end
   wait(0)
end

[Machete]

Nevermind, I finally found a way to do it, rotating "rot" 90 degrees around y. Vincent, do you have a last name you can send by private message? I'm using this script in my thesis and I want to give you credit

In case anyone cares (sorry for the crappy coding):

Code: Select all

-- Title: Display current RA/Dec and attitude information for the center of the FOV

KM_PER_LY = 9460730472580.8
KM_PER_AU = 149597870.7
PI = math.pi
degToRad = PI / 180;
J2000Obliquity = 23.4392911 * degToRad
fov=math.rad(21.534638888888890);

LOOK  = celestia:newvector(0, 0, -1)
earth = celestia:find("Sol/Earth")

-- Convert coordinates from cartesian to polar:
xyz2rtp = function (x, y, z)
   local r = math.sqrt(x * x + y * y + z * z)
   local phi = math.atan2(y, x)
   local theta = math.atan2(math.sqrt(x * x + y * y), z)

   return r, theta, phi
end

-- Return current distance of observer from Earth:
getR = function (obs)
   return earth:getposition():distanceto(obs:getposition())
end

-- Return current RA, Dec for observer:
getRADec = function (obs)
   local base_rot = celestia:newrotation(celestia:newvector(1, 0, 0), -J2000Obliquity)
   local startracker_rot = celestia:newrotation(celestia:newvector(0, 1, 0), -1.5708)
   local rot = obs:getorientation() * base_rot
   local attitude_rot =  rot * startracker_rot
   local look = rot:transform(LOOK):normalize()
   local r, theta, phi = xyz2rtp(look.x, look.z, look.y)
   local phi = math.mod(720 - math.deg(phi), 360)
   local theta = math.deg(theta)
   if theta > 0 then
      theta = 90 - theta
   else
      theta = (-90 - theta)
   end
   return phi, theta, attitude_rot, look.x, look.y, look.z
end

km2Unit =
   function(km)
      local sign, value, units
      if km < 0 then sign = -1 else sign = 1 end
      km = math.abs(km)
      if km > 1e12 then
         value = km / KM_PER_LY
         units = "ly"
      elseif km >= 1e8 then
         value = km/KM_PER_AU
         units = "AU"
      else
         value = km
         units = "km"
      end;
      return string.format("%.2f", sign * value).." "..units
   end

deg2dms = function(deg)
   local   a = math.abs(deg)
  local   d = math.floor(a)
   local   r = (a - d) * 60
   local   m = math.floor(r)
   local   s = (r - m) * 60
   if deg < 0 then d = -d end
   return string.format("%0.0fd %02.0f' %2.0f''",d,m,s)
end

deg2hms =   function(deg)
   local   a = math.abs(deg / 15)
  local   d = math.floor(a)
   local   r = (a - d) * 60
   local   m = math.floor(r)
   local   s = (r - m) * 60
   return string.format("%0.0fh %02.0fm %2.0fs", d, m, s)
end

quat2euler =   function(qtrn)
   local   q4 = qtrn.w
   local   q2 = -qtrn.x
   local   q3 = qtrn.y
   local   q1 = qtrn.z
   local   yaw = math.atan2 (2*(q1*q2+q4*q3),((q4^2  + q1^2 - q2^2- q3^2)))
   local   pitch= math.asin(-2*(q1*q3-q4*q2))
   local   roll= math.atan2(2*(q4*q1+q2*q3),(q4^2  - q1^2 - q2^2+ q3^2))
   yawdeg = yaw/degToRad
   pitchdeg = pitch/degToRad
   rolldeg = roll/degToRad
   
   return yawdeg, pitchdeg, rolldeg
end

while true do
   
   obs = celestia:getobserver()
   obs:setfov(fov)
   obsR = getR(obs)
   obsRA, obsDec, quat, xobs, yobs, zobs = getRADec(obs)
   yaw, pitch, roll = quat2euler(quat)
   celestia:print(obsR..' '..obsRA..' '..obsDec)
   if obsR >= 0 then
      -- Display geocentric coordinates for observer:
      obsRStr = km2Unit(obsR)
      obsRAStr = deg2hms(obsRA)
      obsDecStr = deg2dms(obsDec)
    
     celestia:print("\nRA: "..obsRAStr.."\nDec: "..obsDecStr.."\nq4: "..quat.w.."\nq1: "..quat.z.."\nq2: "..-quat.x.."\nq3: "..quat.y.."\nRoll: "..roll.."\nPitch: "..pitch.."\nYaw: "..yaw, 1, -1, -1, 1, 12)
      --celestia:print("\nRA: "..obsRAStr.."\nDec: "..obsDecStr.."\nq4: "..quat.w.."\nq1: "..quat.z.."\nq2: "..-quat.x.."\nq3: "..quat.y.."\nRoll: "..roll.."\nPitch: "..pitch.."\nYaw: "..yaw.."\nx: "..xobs.."\ny: "..yobs.."\nz: "..zobs, 1, -1, -1, 1, 20)
     --celestia:print("\nRoll: "..roll.."\nPitch: "..pitch.."\nYaw: "..yaw, 1, 1, -1, 1, 8)
   end
   wait(0)
end

[starcreator]

Hi.

I have never do a script for celestia. Do you have a tutorial or a manual for the LUA language?
Anyway, I can't download that script. It gives me the 404 advice.

thanks.
mike

[Vincent]

mike,

I have never do a script for celestia. Do you have a tutorial or a manual for the LUA language?

A tutorial for Celx/lua scripting is available on the Celestia Wiki:
http://en.wikibooks.org/wiki/Celestia/C ... ua_Methods

Anyway, I can't download that script. It gives me the 404 advice.

I've moved to another ftp host. The new link is:
http://vincent.giangiulio.perso.sfr.fr/ ... A_Dec.celx

[selden]

Mike,

Another place to look is here on the forum, in the topic titled "A Preliminary Scripting FAQ". It's at the top of the Celestia Scripting Forum. It includes links to CEL and CELX examples and documentation.