Celestia Forums

Hi guys...

I don't suppose that anyone has made an add-on of the nebula IC 410? I've looked around and haven't found anything, but I was hoping someone might have one that they've never uploaded. I wanted to use it as a backdrop for a system I'm working on.

If not... is there a tutorial on how to make just a simple "billboard" nebula add-on? It's not really what I want, but I'll settle for it for now, if only to achieve the visual impact that I'm looking for.

Thanks for any responses!

...John...

You just need to remove from the nebula photo the background (space) and save it as a png with alpha, then map it on whatever flat meshe...

Probably a dumb question, but where is "alpha"? I'm using PSP, and can't find it anywhere.

...John...

One other quick question: I have the nebula and the star system located at the same RA and Dec. The only difference is the star is 300 light years closer to Sol.

So why does the nebula and the star appear in different parts of the sky?

...John...

Here is the revised IC catalog entry that has the most accurate coordinates and official characterization entries

IC410 * 8 AUR 05 22 44.0 +33 24 40 7.5 25.00 OCL+EN NGC 1893 OCL 439 LBN 807

i.e.
constellation AURIGA
max diameter = 25.0 arc minutes
visual magnitude = 7.5
Rect(2000) = 5h22' 44.0"
Decl(2000) = +33deg24' 40"
Type= Open star cluster + emission nebula
Main equivalent designation: NGC 1893
Emission nebula: H-alpha (obviously, see following image)

http://www.sidus.org/HAlfa/pagine/ngc18 ... 7-916.html
http://www.starrywonders.com/ic410cm10large.jpg

Bye Fridger

John,

Don't forget that STC catalogs require you to specify RA in degrees while DSC catalogs need it to be in hours.

1 hour = 15 degrees.

Dollan wrote:Probably a dumb question, but where is "alpha"? I'm using PSP, and can't find it anywhere.

...John...

just work on a layer, remove the background layer, remove the background of your image, save as png...

Alright, I figured out the positioning problem, though I'm not certain how to write the RA and Dec into a form that Celestia uses, so I kind of eye-balled it for right now.

Now my big problem is that I can't get a texture to take. In a dsc file, can you use Texture "texture.png"? Or do you have to use a program such as animator to assign the texture?

This is what I have thus far:


...John...

John, you are not a newbie... but I must ask why don't you look at one of the existing addon of that kind? you will find all the solution you need...

To map a pict on a mesh you do need a 3D soft...

Unfortunately, DSC files don't accept a Texture declaration.

One way to change what surface texture images are used by a 3DS model is to use a binary (hex) editor. Or you can use Anim8or or some other 3D modelling software.

If you use an ASCII CMOD model, then you can use any text editor to change its surface texture images.

These possibilities are described in
http://www.lepp.cornell.edu/~seb/celest ... board.html
and in
http://www.lepp.cornell.edu/~seb/celest ... -cmod.html

ElChristou wrote:John, you are not a newbie... but I must ask why don't you look at one of the existing addon of that kind? you will find all the solution you need...

To map a pict on a mesh you do need a 3D soft...

That's actually what I did with this. But, never having tried this from scratch before, I had questions that, while simple in nature, tend to be so much so that there's really no documentation on them. For instance, I had no clue that DSC files did not accept the texture declaration. I had a hunch, but without knowing that this was the precise reason for the problem, I still had to operate on the assumption that there could have been a problem with my coding. And with the various art programs, I'm learning more and more all the time.

It's remarkable to note that I've learned more about Photoshop and PSP since I've started using Celestia than at any other period of my computer-usage life!

...John...

selden wrote:Unfortunately, DSC files don't accept a Texture declaration.

Alright, that clears things up tremendously. I had a hunch, but I was still going nuts trying to figure out if there wasn't some other problem!

One way to change what surface texture images are used by a 3DS model is to use a binary (hex) editor. Or you can use Anim8or or some other 3D modelling software.

Alright, I'll work on that this afternoon. I imagine that this tentative move of mine towards having such backgrounds for an add-on will help me learn Anim8tor (probably to Steve and Jestr's relief; I bug them about models far too much!). However, it's gonna be a while before I learn to use modelling software to the extent that you guys do. It will be a fun learning curve, though.

These possibilities are described in
http://www.lepp.cornell.edu/~seb/celest ... board.html
and in
http://www.lepp.cornell.edu/~seb/celest ... -cmod.html

Oh yes, I've already referenced that page quite a bit! And thank you for providing those 3ds meshes and examples on that page. It has helped tremendously.

...John...

t00fri wrote:Here is the revised IC catalog entry that has the most accurate coordinates and official characterization entries...

I forgot to thank you for this! I do have one question, though, which is probably exceedingly simple for you, but up until now I've never run into the need to learn it: How does one translate arc minutes into light years? I've searched out Google, but haven't found anything that helps. If you have any links, that would be most appreciated.

For now, I've used a diameter of 200 light years for IC 410. Not that this needs to be exceedingly accurate, but I'd like to be at least close!

...John...

Don't forget that Chris Laurel wrote a utility to convert 3DS models into ASCII CMOD format, so that's one way to avoid using a binary editor if all you want to do is change the image file name.

It's available in http://www.celestiaproject.net/~claurel/celestia/cmodtools/

The utility asks for libpng1.dll... which I can't find anywhere.

Put the binary in the same directory with Celesita. There's a copy of libpng1.dll there.

John,

converting an angle on the sky (in arc-minutes or otherwise) into a Radius is "simple" trigonometry.

Radius = Distance * Tan(Theta)

Where Radius and Distance have the same units, Tan is the trigonometric Tangent function, and Theta is the angle on the sky corresponding to the radius of the object.

(Check to see if the angle is for the radius or diameter of the object so you don't accidentally double its size.)

Also make sure that the angle is in the units required by the tangent function that you're using. This could be either degrees or radians, so you'll have to look at the documentation.

Dollan wrote:The utility asks for libpng1.dll... which I can't find anywhere.

I've also learned that many programmers use the same dlls. Sometimes you can do a search on your computer and find what you need is already there...