Sky grids and polar axes

[Evil Dr Ganymede]

I'm just planting this idea to see if anyone is capable of doing this as an add-on, because I have no idea how to go about it myself:

What I'd like to see is an add-on consisting of:

a) a spherical grid that encircled a planet just above its atmosphere. Kinda like the celestia grid in Celestia, but this one would be 'personalised' for each planet, so that the equator of the grid corresponded to the equator of the planet. Since it's confined to the top of the planet's atmosphere (or 100 km above the surface, whichever is more appropriate), it'd only be visible in the sky from the surface of that world. (maybe the current Celestia grid could be replaced by this method, even)

b) an 'axis' (a long, thin, white cylinder) that goes through the planet's rotation poles and sticks out of either end of the planet, so you can see where the axis is pointing in space when you're in orbit.

Anyone got any idea how to make these at all? I know Selden's made his galactic co-ordinate grid...

[maxim]

The grid would be easy if only one could define transparent planets.

maxim

[Guest]

I don't know if this is similar to what your looking for or not, but goto Celestiamotherlode and look under the textures for the Sun. The author has created a texture that fits around the original sun texture and rotates in step with the original texture. Maybe this could be modified to suit your need. I think it is cool the way the author did this and it doesn't seem to affect the sun when viewing from the surface. Anyway, have a look and see what you think.

[Evil Dr Ganymede]

Wasn't Selden's grid a model file?

Hmm.

Checking his code, available from here:

# 10degree galactic coords

Nebula " " {
Mesh "10deg.cmod"
Axis [-0.679381 0.221716 -0.699488] Angle 196.475
Position [ 0.00326167 0.0 0.0 ]
Radius 1.0e19
}

I guess it should be possible to fit this grid around a planet by scaling the radius down, but what about the Axis and Position values? It looks like a such a grid would have to be fixed in space, which means it can't orbit a star like a planet does. (bear in mind I have no idea how models are placed in Celestia, so there may well be a way to do this that I'm unaware of).

[selden]

Oh Evil One,

In principle my galactic, etc. coordinate grids can be used as SSC objects around planets. But you're right, it'd be best if planet-specific equatorial grids were available.

[Evil Dr Ganymede]

So could I just define the grids as Mesh instead of Nebula and fiddle around with the parameters and that would work?

[maxim]

Hm, I think you will have to attach the mesh to something.
Perhaps an asteriod or spacecraft definition can do it?
With appropriate size and rotation?

maxim

[Evil Dr Ganymede]

Ideally I'd attach the mesh to a planet...

I'll see what I can do with this tonight or over the weekend.

[selden]

Chris made substantial improvements in how adjacent models are handled for v1.3.2. You can define a second "planet" that uses a Mesh declaration and that has a larger radius but exactly the same orbital and rotational parameters as the original. The Mesh will properly surround the original planet..

Unfortunately, I just remembered that the orientation of the CMOD mesh used for the coordinate spheres is wrong. This is compensated for in the DSC declaration, but it'll be glaringly obvious when you use it in an SSC.

I've been planning to create one with the correct orientation, but haven't had a chance to do that yet. RSN.

[maxim]

It's new to me that one can define a 'planet' to be transparent. IHMO attaching a mesh onto a 'planet' would end up in a white surface with a mesh over it.
That's why I proposed a 'asteriod' or 'spacecraft' with a (spherical) mesh attached.

maxim

[rthorvald]

Chris made substantial improvements in how adjacent models are handled for v1.3.2. You can define a second "planet" that uses a Mesh declaration and that has a larger radius but exactly the same orbital and rotational parameters as the original. The Mesh will properly surround the original planet..

Yes, this is the method i used for several objects in Ran. For example, i attached the cloudlayer to the Bawor station by using a transparent 3ds model on top of the asteroid.

If you have the grid, you can attach it to this model, and define it as a cloudmap. Then define the model as a planet like Selden suggests. The results will be a transparent planet surrounding the real one.

I put the model up here:
http://runar.thorvaldsen.net/celestia/downloads/th_placeholder.3ds (5kb)

- rthorvald

[selden]

Maxim,

To be precise, you don't define a planet to be transparent. Celestia doesn't have that as an SSC option.

Rather, you can create a 3D model that has transparent regions. Then you can use that as a planet's Mesh.

[selden]

Oh, Evil One,

I've created an Addon for drawing axial lines.
See http://www.shatters.net/forum/viewtopic.php?p=46047#46047

[selden]

Oh, Evil One,

I've created an Addon which, with some editing, can be used to draw equatorial grids around planets. It uses Mars as an example.

See http://www.shatters.net/forum/viewtopic.php?p=46060#46060

Here's an example of an Axis and sky and planetary equatorial grids drawn around Mars:

[maxim]

That opens new horizons.

maxim