Celestia Forums

First I'd like to thank Chris and eveyone else who contributed in cranking out v1.3.1 final. I just d/l'd it and can't wait to get home from work to go for a spin!

Now the question: When creating a galaxy or nebula add-on, where can I find or calculate the radius value in the .dsc file? I understand this unit is in light years but couldn't find any info from searching the forum or most of Selden's resources. For example, the SEDS Messier Catalog lists the "Apparent Dimension" in arc-min as well as brightness and distance. Can the radius be calculated from this or other parameters?

Thanks and Happy Holidays everyone,
Dave

Dave,

The radius you need to put into a DSC file is the effective radius of the 3DS object you're putting into Celestia. It is only vaguely related to the astrophysical radius of the object that's in the sky.

I usually start with the astrophysical value, but then change it until my reference picture of the object matches the stars in Celestia as seen from the Earth. If the 3DS model is a different shape from the picture that's been positioned, then you have to twiddle its diameter until its image matches that picture; again as seen from the Earth.

You also have to twiddle the angular orientation and its RA and Dec coordinates, since the centers of pictures seldom correspond to the centers of the objects themselves.

The procedure that I use is described at http://www.lns.cornell.edu/~seb/celestia/billboard.html#6.0

Does this help?

Hi Selden,

Thanks for the response, it does help. That's kind of what I was figuring but wanted to make sure I wasn't missing something obvious.

I have been using the procedure described on your website to align objects. Although the procedure is very straight forward it seems to take me many cycles to get the alignment correct. I'm anxious to try v1.3.1 to see if it handles aligning things better that v1.3.0.

Thanks!
Dave

That was me, shatters.net logged me out in the middle of my post........

Dave wrote:I have been using the procedure described on your website to align objects. Although the procedure is very straight forward it seems to take me many cycles to get the alignment correct.

That is also the case for me
It is very frustrating, especially when I'm trying to align a picture that's slightly distorted.

At one time Chris mentioned that he might be able to add an interactive position adjustment for RA, Dec and Radius, similar to the one currently available for Axis and Angle.

Unfortunately, that hasn't happened yet.