Celestia Forums

Hello,
I petty new to this stuff (CELESTIA) but I am a vetran programmer.
I was disappointed when I zoomed into my first nebula. This 'bumped' flat image was not very realistic to me. I realize that we really have no idea of how these nebulae are dimensioned, yet, one can imagine that these are sparse at their edges and grow more dense toward their centers. Is this right?

I was recently toying around with some nebulae definition files (SSC) along with the model (nebula.3ds) the other day and I actually was able to build a 3-D nebular cloud. It was quite complicated; I used several instances of the model at different sizes and orientations. Is there an easier way to do this?

While not a direct answer to your question, there *are* some wonderful 3D nebulae available at the Motherlode. Go to http://www.celestiamotherlode.net/ and look for some of the ones created by Jll.

...John...

AZ_Cowboy wrote:Hello,
I petty new to this stuff (CELESTIA) but I am a vetran programmer.
I was disappointed when I zoomed into my first nebula. This 'bumped' flat image was not very realistic to me. I realize that we really have no idea of how these nebulae are dimensioned, yet, one can imagine that these are sparse at their edges and grow more dense toward their centers. Is this right?

I was recently toying around with some nebulae definition files (SSC) along with the model (nebula.3ds) the other day and I actually was able to build a 3-D nebular cloud. It was quite complicated; I used several instances of the model at different sizes and orientations. Is there an easier way to do this?

When you write "nebulae", do you mean nebulae or rather galaxies? Give me a ngc number as an example. Don't forget that Celestia incorporates 10000+ galaxies with full info about orientation, sizes, Hubble types, generic colors etc from the most up-to-date scientific catalogs...

Also as to galaxies, one first has to LEARN how to display them correctly. The point here is that most galaxies are very dim compared to the limiting star magnitude that Celestia displays.

Bye Fridger

AZ,

Determining the actual 3D shapes of gaseous nebulae is a topic of current and ongoing scientific research. See, for example, http://arxiv.org/abs/astro-ph/0509699

Some nebulae have "obvious" shapes. For exemple, many are bubbles blown into a surrounding cloud of dust and gas by the light and stellar winds of stars recently formed within them, but partially obscured by clouds between us and them which have not yet completely dissipated.

Others are much more complex and not so obvious

Selden, et al:

Yes, this is what I meant by nebulae. An example would be the Orion Nebula.

cloud of dust and gas by the light and stellar winds

I will have to visit the link that you have posted here. thank you.

I still pose the question about displaying these objects in CELESTIA. I learned today that it's not a bump image that creates the "wrinkle paper" object that has been used for some.

Still learning...

I'm not sure what you mean by a 'bump image'.

Bumpmaps cannot be used for models in Celestia.
Normalmaps have to be used instead -- and they will not be usable until v1.5.0 becomes readily available. The 3D Nebula models that are currently available are shaped entirely by the locations of the vertices in the models.

However, one can create a model from a bumpmap if one uses an appropriate utility to translate bumpmap values into coordinate positions for the vertices in the model.

Unfortunately, Mesh objects declared in DSC files are not drawn as well as one might like. Celestia does not (yet?) depth sort Nebula models. Nebula models and their vertices are drawn in the order that Celestia reads them. As a result, a Nebula model may look reasonable from one viewpoint, but look very strange from another.

AZ_Cowboy wrote:Selden, et al:

Yes, this is what I meant by nebulae. An example would be the Orion Nebula.

cloud of dust and gas by the light and stellar winds

I will have to visit the link that you have posted here. thank you.

I still pose the question about displaying these objects in CELESTIA. I learned today that it's not a bump image that creates the "wrinkle paper" object that has been used for some.

Still learning...

So what you mean are so-called 'diffuse' nebulae. These are the hardest for 'mass rendering', since they don't have a definite shape (hence the name). Bipolar planetary nebulae, for example, are way easier since they have an axial symmetry such that the 3d shape can be generated by computer from a 2d template image like we do it for galaxies.

Note that rendering individual objects via addons may be fun for some, or be useful educational illustrations, but the real task is to implement complete scientific catalogs of deep sky objects into Celestia.

Bye Fridger

Selden:

Bumpmaps cannot be used for models in Celestia.
Normalmaps have to be used instead -- and they will not be usable until v1.5.0 becomes readily available. The 3D Nebula models that are currently available are shaped entirely by the locations of the vertices in the models.

However, one can create a model from a bumpmap if one uses an appropriate utility to translate bumpmap values into coordinate positions for the vertices in the model.

Unfortunately, Mesh objects declared in DSC files are not drawn as well as one might like. Celestia does not (yet?) depth sort Nebula models. Nebula models and their vertices are drawn in the order that Celestia reads them. As a result, a Nebula model may look reasonable from one viewpoint, but look very strange from another.

After talking briefly off-line with Fridger, it seems that you are the person that I need to talk with about the cmod structures. Could you send me an e-mail and we can discuss my proposal?