Celestia Forums

I have an idea for the nebulas: we can represent them like the galaxies in Celestia 1.4.1. So they are more realistic and also in 3-D.

It is possible in any way?

Regards

Matteo

Matteo wrote:I have an idea for the nebulas: we can represent them like the galaxies in Celestia 1.4.1. So they are more realistic and also in 3-D.

It is possible in any way?

Regards

Matteo

Don't understand what you have in mind. Yes, we will be using Sprites as well, but --unlike nebulae-- galaxy shapes can be rendered via a small set of Hubble classification templates. That is hardly possible for nebulae, since these have largely irregular shapes. Also in some other thread that you may find with the search engine, I discussed special possibilities for bipolar planetary nebulae. The latter do have more symmetries which may be exploited. The rendering of galactic clusters is straightforward and will come next, after galaxies have been finalized.

So what was your idea again?

Bye Fridger

You should first do a search on a topic, this idea has been posed and discussed. I will give you the short nitty gritty version.

10,000 galaxies are represented in Celestia using less than ten models. That is possible due to the fact that galaxies can be catagorized by their shape.

Nebulae, barring planetary nebulae, could never be categorized by overall shape. Therefore the idea of doing the same thing as galaxies is not possible.

We do not know the 3d shape of nebulae. It can be inferred to a degree through visual cues, and radio density maps, but in general reflection and emission nebulae are very, forgive me, nebulous.

Jll has done some very nice 3d representations of various nebulae. It takes a ton of work and the results, though stunning, are a) not exact in their 3d configuration b) not what we would see with our eyes and c) limited by the rendering engine of the software to produce that cloudy quality one would look for in a nebula.

Some of Jll's work is here:
http://celestiaproject.net/forum/viewtopic.php?t=9656
http://celestiaproject.net/forum/viewtopic.php?t=9034
http://celestiaproject.net/forum/viewtopic.php?t=8369
http://celestiaproject.net/forum/viewtopic.php?t=7974
http://celestiaproject.net/forum/viewtopic.php?t=7061

I read and checked out the links to this and previous threads on this topic. The models that Jll has made are impressive but still a guess to the shape. Had an idea on how to display nebula in celestia. I work with simulators and one trick that is used is to have to flat polygon with the image always facing the camera or POV. It is called billboarding. Can polygons (models) be targeted to alway face the camera?

I realize that nebula are 3D but we don't really know what they look like other that the POV from Earth. So this would only show that POV even if the person flys completely around it. The model files would be much smaller (two triangles forming a square that the image is mapped too). Most of the known nebula could be part of the standard download.

Just my 2-Cent fix to a complex problem.

Don

It really wouldn't satisfy one of the main goals of Celestia, visible light 3d viewing. Having something look the same from every angle defeats the purpose of 3d exploration and visualization of the universe. Right now it would be possible to collect a database (similar to Fridger's 10000 dsc file) of different types of nebulae for future inclusion, this way we would have locations/markers visible for all objects. I am unsure if this has been done or not. Anyone?

buggs_moran wrote:It really wouldn't satisfy one of the main goals of Celestia, visible light 3d viewing. Having something look the same from every angle defeats the purpose of 3d exploration and visualization of the universe. Right now it would be possible to collect a database (similar to Fridger's 10000 dsc file) of different types of nebulae for future inclusion, this way we would have locations/markers visible for all objects. I am unsure if this has been done or not. Anyone?

This is practically trivial, using my PERL script for DSO extraction from the revised NGC/IC catalog. I have prepared it such that eventually we will have the NGC/IC completely integrated in Celestia. For my PERL script I just need to change the respective type flag and then get the complete catalog of gaseous nebulae, planetary nebulae, galactic clusters ...instead of the 10000+ galaxies from the rev. NGC/IC, with complementary data from 6 further catalogs that are exploited during the read-out.

That list is definitely very high up on my todo list.

However, given the recent unpleasent ongoings in this forum, I will essentially stop giving feedback of my dev activities here. My stuff will go directly to dev and CVS and soon also to CM, of course. One active column I am planning to maintain in CelestialMatters, will be about:

"Celestia Dev Matters"

Here I shall give a regular account of what is up in Celestia development.

I don't see much of a good reason for investing my time here anymore, after Selden's insisting, P&A policiy decisions etc.. Sorry.

cf. http://www.celestiaproject.net/forum/viewtopic.php?t=9743

Bye Fridger

I can't help but include, as I have in the past, an idea I have for these nebulae. Take two spherical globules (similar to the pts points in the galaxies) to represent gas and dust in a nebula.

Give the gas glob these characteristics:
1) 1/distance to star = glow reddish in emission (the degree of glow would need to be inversely proportional to distance and star type.)

Give the dust glob these characteristics:
1) between observer and star = extinguish/redden light from star
2) near a star = glow bluish in reflection

Now do hundreds of globs to represent a nebula. I realize you would not have absolute structure control, but you could essentially "build" nebulas to fit the "look" that we see.

I believe you would have to use volumetric rendering (a topic I know nothing about) to accomplish this.

buggs

I can't give you the code level info on volumetric rendering. I use Lightwave in part of my work. Maya, 3D Max, SoftImage to name a few also provide this capability but it is in the raytrace or render side of the application. Even with a fast machine rendering a volumetric cloud like a nebula can take minutes. This would completely kill the real time effect of Celestia. The results whoever are stunning. I will add that as video cards evolve volumetric effects will become more possible.

I think I understand your idea with the points. Is this how the galaxies are currently being display in Celestia? I could easily generate a point cloud in any shape or shapes if you know how to assign the glow based upon a distance function. Lightwave can assign meta-data to points that could be a function of glow color but I don't know if this can be converted into meaningful data in the 3DS format. Will have to experiment. If you want to try this let me know which nebula to model and approx how may points would do.

Don

Hello

I think the representation of nebulas in Celestia must solve many challenges :
- real time visualization : require ?€?light weight?€