Celestia Forums

Posted: **14.09.2010, 20:26**

There is a script to give the observer their RA, Dec and distance in space but could somebody possible make one that will give you your coordinates in a format that the Celestia STC files use? That is, if it's not a huge task to make one and if one doesn't already exist.

Posted: **15.09.2010, 17:17**

Hi Reiko,

if you already have a scrit that gives you the R, Dec and distance you don't need another script.

Just take the values and report them in your *.STC file.
In a stc file, RA and dec are in decimal degrees and distance is in ly.

For example if your RA is has the form "h, min, sec" just convert it in degree with the formula
RA(degree) = (( h * 15 + mn)*60 + sec ) *60)

Posted: **15.09.2010, 17:46**

I know how to convert them but would like a script to show my position in those coordinates.

Here is the script I've been using made by Vincent found here. viewtopic.php?f=9&t=12209&hilit=displaying+position

Code: Select all

-- Title: Display current RA/Dec for observer

KM_PER_LY = 9460730472580.8;
KM_PER_AU = 149597870.7;
PI = math.pi
degToRad = PI / 180;
J2000Obliquity = 23.4392911 * degToRad

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)
    local d = (earth:getposition():distanceto(obs:getposition()))
    return d
end

-- Return current RA, Dec for observer:
getRADec = function (obs)
    local base_rot = celestia:newrotation(celestia:newvector(1, 0, 0), -J2000Obliquity)
    local rot = earth:getposition():orientationto(obs:getposition(), LOOK) * 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
end

km2Unit =
    function(km)
        local sign, value, units
        --if not (type(km) == "number") then return km end;
        if km < 0 then sign = -1 else sign = 1 end;
        km = math.abs(km);
        if km > 1000000000000 then
            value = km / KM_PER_LY
            units = "ly";
        elseif km >= 100000000 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("%0.0f %02.0f' %04.2f'' (%0.3f)",d,m,s,deg);
    return string.format("%0.0f° %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

while true do
    obs = celestia:getobserver()
    obsR = getR(obs)
    obsRA, obsDec = getRADec(obs)
    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("Geocentric coordinates for observer:\nR: "..obsRStr.."\nRA: "..obsRAStr.."\nDec: "..obsDecStr, 1, -1, -1, 1, 7);
    end
    wait(0)
end

Could it be modified to show your coordinates in the format that the STC files use?

Posted: **15.09.2010, 18:20**

just a little modification to the previous code :

Code: Select all

    -- Title: Display current decimal RA/Dec for observer

    KM_PER_LY = 9460730472580.8;
    KM_PER_AU = 149597870.7;
    PI = math.pi
    degToRad = PI / 180;
    J2000Obliquity = 23.4392911 * degToRad

    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)
        local d = (earth:getposition():distanceto(obs:getposition()))
        return d
    end

    -- Return current RA, Dec for observer:
    getRADec = function (obs)
        local base_rot = celestia:newrotation(celestia:newvector(1, 0, 0), -J2000Obliquity)
        local rot = earth:getposition():orientationto(obs:getposition(), LOOK) * 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
    end

    km2Unit =
        function(km)
            local sign, value, units
            --if not (type(km) == "number") then return km end;
            if km < 0 then sign = -1 else sign = 1 end;
            km = math.abs(km);
            value = km / KM_PER_LY
            units = "ly";
            return string.format("%.5f",sign*value).." "..units;
        end


    deg2str =    function(deg)
        return string.format("%0.6f deg", deg);
    end

    while true do
        obs = celestia:getobserver()
        obsR = getR(obs)
        obsRA, obsDec = getRADec(obs)
        celestia:print(obsR..' '..obsRA..' '..obsDec)
        if obsR >= 0 then
            -- Display geocentric coordinates for observer:
            obsRStr = km2Unit(obsR);
            obsRAStr = deg2str(obsRA);
            obsDecStr = deg2str(obsDec);
            celestia:print("Geocentric coordinates for observer:\nR: "..obsRStr.."\nRA: "..obsRAStr.."\nDec: "..obsDecStr, 1, -1, -1, 1, 7);
        end
        wait(0)
    end

Posted: **15.09.2010, 19:05**

YAY!! Thank you!

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