Celestia "FixedPostion" Coordinate System Help

[CM1215]

Hello,

I am trying to modify Jestr's old Deep Impact addon to work with the new Tempel 1 mesh that is currently available, but I can't get the explosion/debris to appear where I want it. I need to know more about how to use the "FixedPosition" entry to place the explosion/debris right where it needs to be. I've been experimenting with this and don't understand the coordinates, for it doesn't seem to work right with the latitude and longitude coordinates that I put into it, even when I have it set to Planetographic coordinates.

Can someone please help me with this?

Thanks,
CM1215

[selden]

Please provide a copy of the failing Addon.

[CM1215]

Alright then. Here is the addon:

DeepImpactAddon.zip

(20.23 MiB) Downloaded 229 times

I had already tried to experiment with the coordinates, but the explosion/debris never appear right were I want them to appear, which is right where the impactor crashes into Tempel 1.

[selden]

One way to do it would be to define an object (with an appropriate orientation) on the surface of Tempel 1 which corresponds to the impact point, then define debris ejecta relative to that object, not relative to Tempel 1. That way you can separate the debugging of the ejection process from placing and orienting it appropriately.

Don't put time constraints on that location, only on the debris itself.

The surface of Tempel1's mesh is irregular, but placement of the object is relative to a sphere with the defined radius, so you have to specify an altitude which compensates for the irregularity of the Mesh's surface relative to the ideal sphere's surface. Trial-and-error will be needed to find the correct placement and orientation of the object. After it's working the way you want, you can make the object Class "invisible".

[CM1215]

Perhaps you could give me an example of this?

[selden]

To define an object that can be used as impact point, Insert these definitions at the end of "Tempel 1.ssc". They define a red sphere that can be used for placement of ejecta. As a simple example, the code also defines a piece of ejecta as a yellow sphere at a fixed location relative to the impact point. I'll have to leave it to you to define appropriate ejecta with appropriate trajectories.

Edited to add: the small green diamond above the red sphere is the Impactor. You'll have to adjust the position of the impact site to get it exactly right.

Code: Select all

SurfaceObject "an_impact_site" "Sol/Tempel 1"
{
   Radius 0.01
   Color [ 1 0 0 ]

   OrbitFrame { BodyFixed {} }
   FixedPosition
   {
       Planetographic [ -200.5 -22.0 -1.03 ]
   }
   FixedRotation {}
}

SurfaceObject "ejecta" "Sol/Tempel 1/an_impact_site"
{
   Radius 0.002
   Color [ 1 1 0 ]

   OrbitFrame { BodyFixed {} }
   FixedPosition
   {
       Planetographic [ 0 90 0.01 ]
   }
   FixedRotation {}
}


If you go to this URL:

impact site

You should see this

[FarGetaNik]

That reminds me, I may have never properly published my Deep Impact addon. I used the new mesh for Tempel 1 and defined a trajectory that resultet in an impact pretty close to where it was supposed to be...

[CM1215]

That reminds me, I may have never properly published my Deep Impact addon.

You are probably right, because I didn't even know that you had a Deep Impact addon...

Do you know where I can get it?

[FarGetaNik]

It is included in the standard extras for my Project Echoes: https://drive.google.com/file/d/0B14NSu0PnA5xdkpZQWVHYWNFTU0/view
Note that this addon only works with a variety of refernce points. Maybe I should put a proper addon together... or upload it onto the motherlode? The problem is that because I've updated so much of the Celestia content and Celestia 1.7 is in sight I don't even know what to include in this addon.

[CM1215]

Your addon is good, but I have a question:

What orientation parameters did you use for the Tempel 1 mesh? Also, did you pre-orient the model in Anim8or before you converted it?

And a suggestion:

Would it be possible to add impact ejections from the comet's surface like are seen in the impact images?

[FarGetaNik]

What orientation parameters did you use for the Tempel 1 mesh? Also, did you pre-orient the model in Anim8or before you converted it?

I believe you mean the mesh of the impactor? Tempel 1 is not in the extras I linked. I made this addon a while back so I don't know the exact reasoning anymore, but I think it had something to do with the complicated BodyFrame. I guess it could be fixed by rotating the mesh in Anim8or, which is what I always try to do now.

Would it be possible to add impact ejections from the comet's surface like are seen in the impact images?

Well this is your objective right? I don't really know how to do it, but the addon on the motherlode did something like that.