Getting my brain around the billboard mesh

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foravalon
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Getting my brain around the billboard mesh

Post #1by foravalon » 10.01.2011, 20:49

For the goal of my project I'd love to use Selden's billboard mesh with one minor adjustment, Instead of having the face of the billboards directed toward Sol I'd like to have the faces of my billboards lying flat on the plane of the galactic. I have a feeling this is something I can easily accomplish, but I'm having trouble wrapping my head around the definitions in the DSC file and I'm not sure about the best way to accomplish my goal.

Up to now I've been creating my models manually using a connect the dots method, where I plot the point in the model using galactic b2 l2 coordinates and use the nasa HEASARC Coordinate converter to convert those points to the RA and Dec that celestia wants; if there's a more efficient way making these models please give me a holler! Any light which can be shed is always appreciatd.

Any way I'm working with some maps that I'd love to overlay flat on the plane. One way I think I can do this is to use the billboard mesh and change... some perameter to orient it so it's facing directly "up" toward galactic north, I'd imagine I can adjust the size by modifying the radius in the DSC and the distance and position of the center using RA/Dec, but the orientation is the tricky bit for me since I don't really understand what definitions dictate what exactly.

Reading Selden's page has only evoked more questions.

-What is "Celestia's builtin positioning tool" and how does one use it?

-What is the Radius exactly? Is the radius the size of one unit on the length of the side of the billboard? In other words if I'm using a billboard with a radius of 50, will this then create a square 50 lightyears by 50 light years or If I'm using the 2x1 rectangle will it make a billboard 100lys by 50lys?

I know the vertices define the points of the square but I'm unclear on what the trilist defines.

I'm also unclear on what defines the actual positions of those vertices.

Over all I'm quite confused, how do you guys make and orient models? Is there some ideal software for the process?

Here's an example of What I've been able to create using my own methods: http://student.santarosa.edu/~kkieta/2010fall/wrk_Infinite_Diversity%202/filedump/KnownSpace3.4.zip
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selden
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Re: Getting my brain around the billboard mesh

Post #2by selden » 11.01.2011, 14:33

Use of Celestia's builtin orientation tool is explicitly described on the Billboard Web page. See http://www.lepp.cornell.edu/~seb/celest ... d.html#6.0

One option is to turn on Celestia's Galactic coordinate grid and align a billboard to match. The same orientation parameters would then work for any billboard using the same model file.
Selden

Topic author
foravalon
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Location: Santa Rosa, CA

Re: Getting my brain around the billboard mesh

Post #3by foravalon » 11.01.2011, 18:29

Thanks for the tips selden, I get to swimming through the variables and then I lose my way.

Do you have any recommendation for any software for modelling and then translating into celestia. Or do you recommend any methods for coordinate conversion other than the NASA Heasarc site I'm using? Every other aspect of my work is home-brewed using spreadsheets except for that one conversion from galactic to j2000 ecliptic, which I've had a hell of a time finding the equation for and figuring out how to translate it into something I can integrate into my spreadsheet. I hate having to rely on an outside source for such an important aspect of my project.
Foravalon's most common phrase: "So, yeah, um, how do you do this... ?"

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John Van Vliet
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Re: Getting my brain around the billboard mesh

Post #4by John Van Vliet » 11.01.2011, 18:50

--- edit ---
Last edited by John Van Vliet on 19.10.2013, 08:17, edited 1 time in total.

Reiko
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Re: Getting my brain around the billboard mesh

Post #5by Reiko » 11.01.2011, 19:47

Holy smokes that looks great! :D

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selden
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Re: Getting my brain around the billboard mesh

Post #6by selden » 11.01.2011, 20:01

A CMOD export script is also available for Anim8or.

Anim8or is the free Windows 3D modeling program that I use. I think it's much easier to learn than Blender, but it hasn't been updated for a couple of years. As a result, it has some unfixed user interface problems selecting points when it's used under Windows 7. Personally I consider them to be only annoyances, though, since they don't prevent me from creating the models that I want. It doesn't have those problems under XP.

Anim8or: http://www.anim8or.com/
CMOD export script: http://www.lepp.cornell.edu/~seb/celest ... g.html#4.1
Selden


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