Model disappears @ ~ 1 ly distance - Bug or feature?

[Chuft-Captain]

[ in Celestia 1.4.1 ]

As the Rungworld is only 4ly's from Earth, I thought I would try to see what it would look like at a high magnification, from Earth.

Unfortunately, it disappears suddenly and completely when the observer exceeds 1.0002 light years distance, so unfortunately will never be visible from Earth.

To replicate this bug, download and install the Rungworld from the RUNGWORLD link in my Signature below,
then click on THIS URL, and press F6 followed by Q, to back away from the Rungworld.

At 1LY all is well:

but at 1.0002 ly... GONE!


I haven't tried other models, as few of them would be large enough to see from these distances anyway.


Is this a BUG? or is it a deliberate feature, perhaps so that Celestia doesn't try to render distant models?

[selden]

I seem to recall Chris posting some time ago that SSC objects are not rendered when you're more than about a light year from their parent star.

If you want a distant model to be visible from the Earth, it'll have to be defined as a DSC Nebula.

[Chuft-Captain]

Is it actually possible to define SSC type objects in a DSC?
ie. Are all the same commands available in DSC's as in SSC's ?

I always thought only galaxies, etc could be defined in .DSC files.

[selden]

CC,

DSC Nebula definitions are very limited. You can only specify mesh, location, orientation, size and infourl. Here's an example:

Code: Select all

Nebula "NGC 3372" {
        Mesh     "ngc3372.cmod"

    Axis [-0.206916 0.153726 0.966206]
   Angle 154.5

   Distance   8500
   RA      10.7345
   Dec      -59.752
   Radius     219
   InfoURL "http://www.noao.edu/image_gallery/html/im0061.html"   
}

Distance and Radius are measured in LightYears, RA in hours, Dec and Angle in degrees. Axis is a normalized vector (its length =1)

In v1.4.0 or newer you might also be able to specify
AppMag
AbsMag

These were recently added for Galaxy definitions. I don't know if they work for Nebula definitions.

[Chuft-Captain]

Thanks Selden,

That confirms what I thought, which is that the Rungworld will never be able to be defined as a nebula, because it requires SSC commands such as EllipticalOrbit, RotationPeriod, RotationOffset, etc...
(It's also Rigel Kentaurus A centric, whereas I believe DSC objects such as nebulas are all SOL centric)

I did another experiment with this "BUG" which shows that it is not just distance related...

At 1 light-year distance and a FOV of < 1 arcmin, it's visible.
(Click on the image if you have the rungworld installed)


If I then press the "." key once only, to increase the FOV to > 1 arcmin, it disappears (even though distance hasn't changed):