The Galactic Core

[selden]

It also displays OK if you "drag and drop" the avi file onto the DivX v6.7 player.

Evidently DivX botched their current WMV interface.

And when trying to run the XVid installer, Windows complains that the installer is corrupted.

[t00fri]

It also displays OK if you "drag and drop" the avi file onto the DivX v6.7 player.

Evidently DivX botched their current WMV interface.

And when trying to run the XVid installer, Windows complains that the installer is corrupted.

I have no problems with the curent DivX 6.7 player and DivX codec 6.8 bundle.
Both with Drag&Drop and regular file opening. Of course Win Media Player does not like this codec, but this I knew from the start.

F.

[Reiko]

The core?

Correct!

It's a bunch of stars!

Correct!

--- Click for VIDEO (5.5 MB) XVid

PS. The quote is from Larry Niven's short story "At The Core".

I of course knew you meant the core. I was just testing to see if you knew it was the core.
Yup that is my story!



Just kidding! Cool video by the way.

[Reiko]

It also displays OK if you "drag and drop" the avi file onto the DivX v6.7 player.

Evidently DivX botched their current WMV interface.

And when trying to run the XVid installer, Windows complains that the installer is corrupted.

I have no problems with the curent DivX 6.7 player and DivX codec 6.8 bundle.
Both with Drag&Drop and regular file opening. Of course Win Media Player does not like this codec, but this I knew from the start.

F.

You need a better codec pack.
http://www.cccp-project.net/
http://www.free-codecs.com/download/K_L ... c_Pack.htm

[tech2000]

This is the best codec pack for windows...
http://www.free-codecs.com/download/K_L ... c_Pack.htm

Bye, Anders Pamdal

[t00fri]

This is the best codec pack for windows...
http://www.free-codecs.com/download/K_L ... c_Pack.htm

Bye, Anders Pamdal

Many thanks, Anders. That pack really works! Now my WMP playes really plays everything.

F.

[Chuft-Captain]

OK,

Now that everyone has got their codecs sorted, here's some more CORE content...



My S2 in Celestia: http://traitorsclaw.sitesled.com/projects/core/S2-2.avi

Compare with the [url=http://www.eso.org/outreach/press-rel/pr-2002/video/vid-02-02.mpg]ESO video clip of orbiting star (533 KB MPEG Video)
[/url]

Read about S2 here: Surfing a Black Hole and here: S2 (star)

[eburacum45]

So you have made an add-on of the Galactic Center?> Excellent!
I am puzzled though- I thought there was a 16000 ly limit for star locations.

[Chuft-Captain]

I am puzzled though- I thought there was a 16000 ly limit for star locations.

I wondered when someone would notice this.

Fightspit and other people with codec issues...I have made an MPG version of the AtTheCore video for you.

....oh and Fightspit, I forgot to address your issue with the lack of sound:

I can't see anything in your movie even if I have got the Xvid plug-in and there is not sound.

"In space, no-one can hear you scream."

[Cham]

Chuft-Captain, and others (Chris, Selden ?),

please, can you confirm that we can put stars at the center of our galaxy ? What version of Celestia are you using ?

Chuft-Captain, please, show us an example of STC definition which places some stars at the center, farther away from Sol than the 16k limit. I'm simply sceptic about this.

[chris]

Chuft-Captain, and others (Chris, Selden ?),

please, can you confirm that we can put stars at the center of our galaxy ? What version of Celestia are you using ?

Chuft-Captain, please, show us an example of STC definition which places some stars at the center, farther away from Sol than the 16k limit. I'm simply sceptic about this.

No, you cannot place stars at the center of the galaxy. I think that Chuft-Captain may be using a deep sky object with a point sprite cmod file.

--Chris

[Cham]

Ahaa ! That explains why the luminosity isn't decreasing with distance, on his video. What a cheater !

[eburacum45]

I thought that might be the answer too.

[Chuft-Captain]

Chuft-Captain, and others (Chris, Selden ?),

please, can you confirm that we can put stars at the center of our galaxy ? What version of Celestia are you using ?

Chuft-Captain, please, show us an example of STC definition which places some stars at the center, farther away from Sol than the 16k limit. I'm simply sceptic about this.

No, you cannot place stars at the center of the galaxy. I think that Chuft-Captain may be using a deep sky object with a point sprite cmod file.

--Chris

Apart from the fact that I don't have Open-GL 2.0 (which I think is a pre-requisite for point-sprites is it not), and the fact that I'm not clever enough in the modellng department to know how to create a point-sprite model,... how do you explain the fact that at the beginning of the video the stars are all moving independently? (I don't think that this would be possible with a point-sprite model.)

OK, I'm not a cheater (but I am very sneaky).

I'll explain...

Code: Select all

Barycenter   "Sagittarius A"
{
   RA   266.4168333
   Dec   -29.00780555
   Distance   27800
}


followed by...

Code: Select all

"S000001"
{
   OrbitBarycenter   "Sagittarius A"
   SpectralType   "B5"
   AppMag   10.9311615947372
   EllipticalOrbit
   {
      Period      101235.393613888
      SemiMajorAxis   34721264.0892879
      Eccentricity   0.001
      Inclination   85.475389248495
      AscendingNode   278.809319208203
      ArgOfPericenter   197.673190706992
      MeanAnomaly   48.9464256972133
   }
}      

"S000002"
{
   OrbitBarycenter   "Sagittarius A"
   SpectralType   "M2"
   AppMag   6.29450134394574
   EllipticalOrbit
   {
      Period      97146.6250745016
      SemiMajorAxis   11583926.2467687
      Eccentricity   0.001
      Inclination   81.2001278850676
      AscendingNode   59.366941411181
      ArgOfPericenter   92.6424595734352
      MeanAnomaly   53.07533537376
   }
}      

"S000003"
{
   OrbitBarycenter   "Sagittarius A"
   SpectralType   "M2"
   AppMag   3.58840833669092
   EllipticalOrbit
   {
      Period      103244.437658122
      SemiMajorAxis   74152231.7101051
      Eccentricity   0.001
      Inclination   30.3667834943371
      AscendingNode   21.7353924469414
      ArgOfPericenter   23.0584018673835
      MeanAnomaly   283.313002506402
   }
}      

"S000004"
{
   OrbitBarycenter   "Sagittarius A"
   SpectralType   "M6"
   AppMag   9.78134131840488
   EllipticalOrbit
   {
      Period      102556.904939074
      SemiMajorAxis   43721209.7044769
      Eccentricity   0.001
      Inclination   7.21325194516794
      AscendingNode   0.0677790115514654
      ArgOfPericenter   352.150186404833
      MeanAnomaly   148.551800761888
   }
}      

"S000005"
{
   OrbitBarycenter   "Sagittarius A"
   SpectralType   "O2"
   AppMag   3.48782289666269
   EllipticalOrbit
   {
      Period      98812.0859900846
      SemiMajorAxis   87449127.0195768
      Eccentricity   0.001
      Inclination   57.6222577967565
      AscendingNode   72.6447398492019
      ArgOfPericenter   37.0141607235928
      MeanAnomaly   164.556814385578
   }
}      



etc, etc, etc, another 9995 times.


The luminosity issue:
I believe Celestia calculates luminosity from the specified Appmag combined with the star's known distance from Earth. (Apparent magnitude, as I'm sure everyone knows, is the brightness a star would appear if viewed from earth).
With the rather arbitrary Appmags I've currently assigned (I've made no attempt yet to calculate realistic Appmags), most of these stars are already far too luminous.
At the distance of about 25000 LY, in order to get appropriate luminosities they should all have very large positive apparent magnitudes.

I've also made no attempts yet to match SMA with realistic Periods for the orbits (with the sole exception of S2), because there's actually more serious issues to do with rendering which may in fact blow the whole thing out of the water at the end of the day. (see the next paragraph)

The rendering issue:All the stars disappear completely and are not rendered if you don't get the viewpoint right. ie. It's often necessary to rotate the viewpoint in order to get them to render. This is possibly a depth-sorting issue, or something to do with the 16K limit.
I've noticed this before with other distant experimental stars I've placed outside the Milky Way for example.

At this stage I don't know the exact reason for this behaviour. Chris may know more about this.

Anyway, it's a WIP, but I'm open to anyone's advice.

Cheers
CC

[tech2000]

This is the best codec pack for windows...
http://www.free-codecs.com/download/K_L ... c_Pack.htm

Bye, Anders Pamdal

Many thanks, Anders. That pack really works! Now my WMP playes really plays everything.

F.

You're welcome. With that pack installed I have not yet found a media file that wasn't playable in windows media player... It also has codecs to play realmedia and quicktime..

Cheers, Anders

[bdm]

The rendering issue:All the stars disappear completely and are not rendered if you don't get the viewpoint right. ie. It's often necessary to rotate the viewpoint in order to get them to render. This is possibly a depth-sorting issue, or something to do with the 16K limit.
I've noticed this before with other distant experimental stars I've placed outside the Milky Way for example.

Have you seen it with other stars? I have found that one component of Delta Trianguli can be made to blink on and off in a similar manner to that which you describe.

[Chuft-Captain]

I've only seen this happen with stars that are over the 16K limit such as the core stars. (I don't get the problem you do with Delta Trianguli) Also, it seems that the dimmer the star, the worse the problem is.

I haven't got to the bottom of exactly what's going on yet, but it seems that if I use realistic apparent magnitudes for the core stars, then most of them at this distance would be in the range +10 - +29 magnitude, and it seems that the only ones I can then get to render at all (regardless of viewpoint) are the O and B class stars, which are in the range +3.5 - +12 appmag.

If I use un-realistic appmags to make the dimmer stars more luminous, then they do render. Strange...., but I think it's connected in some way with the 16K limit....
Chris... any comment???

The other thing I notice is that the magnitude limit can only be increased to about +15 in Celestia. I assume this has something to do with the dynamic range of your typical display device.

[selden]

CC,

Playing with various of Celestia's parameters isn't going to do you any good. You're wasting your time. They'll change the symptoms slightly, but that's all. You cannot get around the underlying distance design problem until Chris has eliminated it. Although he has a conceptual framework for a solution, it won't be implemented soon.

[Chuft-Captain]

CC,

Playing with various of Celestia's parameters isn't going to do you any good. You're wasting your time. They'll change the symptoms slightly, but that's all. You cannot get around the underlying distance design problem until Chris has eliminated it. Although he has a conceptual framework for a solution, it won't be implemented soon.

Thanks Selden,
I'd pretty much come to the conclusion that the rendering issues was due to the distance limit. I don't understand why they should sometimes render and sometimes not. -- I thought the only issue with exceeding the 16K limit was that you wouldn't be able to position things with any degree of accuracy --- but it seems that there's this little issue with rendering as well.
If I understood the reasons for the rendering issue, I might be able to come up with a sneaky workaround in the meantime (ie. hack) -- I'm quite good at those , but in the absence of any feedback from Chris, this addon will probably have to just go on hold.

[chris]

CC,

Playing with various of Celestia's parameters isn't going to do you any good. You're wasting your time. They'll change the symptoms slightly, but that's all. You cannot get around the underlying distance design problem until Chris has eliminated it. Although he has a conceptual framework for a solution, it won't be implemented soon.

Thanks Selden,
I'd pretty much come to the conclusion that the rendering issues was due to the distance limit. I don't understand why they should sometimes render and sometimes not. -- I thought the only issue with exceeding the 16K limit was that you wouldn't be able to position things with any degree of accuracy --- but it seems that there's this little issue with rendering as well.
If I understood the reasons for the rendering issue, I might be able to come up with a sneaky workaround in the meantime (ie. hack) -- I'm quite good at those , but in the absence of any feedback from Chris, this addon will probably have to just go on hold.

Selden's correct: there are going to be all sorts of problems with placing stars beyond the 16k light year limit. Limited accuracy of single precision floating point arithmetic was the reason for imposing that limit, but loss of precision isn't the only artifact you will see if you try and position stars that far away. I don't think it will be so long before I can address the 16k light year limitation, however.

--Chris