1.2.5 Pre bug report

[chris]

Isn't the way it is more scientifically accurate? But perhaps you're right - I think most comets actually have two tails - one pushed by the solar wind away from the sun and another trailing behind as it moves through space. So more work for Chris, perhaps...

I'll be be posting the next prerelease today . . . comets are significantly different than in the first prerelease. There still aren't separate ion and dust tails. There's a single tail, influence by the orbital path of the comet as well as the solar wind.

--Chris

[billybob884]

I think I found another bug. Sometimes when in celestia, portians of the earths clouds look dark grey. Click here to see a pic > http://www.geocities.com/billbob884/pics2.html. Kinda odd?


Mike M.

[ogg]

Hi, just to confim that I'm getting an old display bug still with the rendering of ring shadows. Here's a screenshot and my OpenGL info:


Vendor: Trident
Renderer: Blade XP/AGP
Version: 1.2.1
Max simultaneous textures: 2
Max texture size: 1024

Supported Extensions:
GL_ARB_multitexture
GL_EXT_abgr
GL_EXT_bgra
GL_EXT_compiled_vertex_array
GL_EXT_packed_pixels
GL_EXT_paletted_texture
GL_EXT_vertex_array
GL_WIN_swap_hint

Chris: earlier you suggested that a checkbox could be added to the view options to enable or disable ring shadows, in the same way that eclipse shadows are. Is this still possible? If so I'd definitely like to request it, because at the moment Saturn and Uranus just look damn ugly on my crappy laptop!

Thanks for the great program, can't wait to see the comet tails in all their glory!

[ogg]

A few questions about possible 'bugs', mostly concerning astronomical accuracy.

1) The schematic comet tails in 125p1 get longer when the comet is further away from the sun. This is the opposite of what really happens... is this the result of an as-yet incomplete calculation?

2) Rings seem to fade to complete darkness when the camera is positioned on the other side of the sun from them. I don't know what Voyager pictures or whatever have to say about this, but it seems to me that this would only be the case if every particle of the ring were perfectly opaque - ie no transmission of light. No doubt most of the ring is made of big, dirty chunks of ice that might as well be rock. But smaller particles would allow more light to travel through them before it was attenuated to nothing... so depending on the dirtiness of the ice, the minimum size of the ice particles (and their number) you'd expect a faint, transmitted, scattered glow to be visible from the 'night side'.
---- the fading should also be a function of the angle between the camera and the sun for each particle/surface element of the ring, rather then have the whole thing fade in unison as a macroscopic object/surface, but I imagine that would be somewhat processor intensive ----

3) I get a strange 'winking' effect concerning the brightness of planets from a distance. To reproduce: move ~35AU away from the sol, centre on sol, and rotate around it. The planets wink on and off (or discontinuously to mid-brightness) rather then waxing and waning smoothly. Might this be related to my display problems in the previous post? This winking behaviour does not happen in 124.

4) Not a bug report but a quiery: earlier, Chris, you suggested that it would be possible in the future to adjust the distance or angular size before orbits were rendered. Is this feature/hack available now?

Hate being this picky... but Celestia's so near to perfect that it makes a pedant out of me.

[chris]

A few questions about possible 'bugs', mostly concerning astronomical accuracy.

1) The schematic comet tails in 125p1 get longer when the comet is further away from the sun. This is the opposite of what really happens... is this the result of an as-yet incomplete calculation?

Fixing this right now . . . . The implementation of comet tails in the frist prerelease was just a work in progress.

2) Rings seem to fade to complete darkness when the camera is positioned on the other side of the sun from them. I don't know what Voyager pictures or whatever have to say about this, but it seems to me that this would only be the case if every particle of the ring were perfectly opaque - ie no transmission of light. No doubt most of the ring is made of big, dirty chunks of ice that might as well be rock. But smaller particles would allow more light to travel through them before it was attenuated to nothing... so depending on the dirtiness of the ice, the minimum size of the ice particles (and their number) you'd expect a faint, transmitted, scattered glow to be visible from the 'night side'.
---- the fading should also be a function of the angle between the camera and the sun for each particle/surface element of the ring, rather then have the whole thing fade in unison as a macroscopic object/surface, but I imagine that would be somewhat processor intensive ----

I model the ring as a distribution of completely opaque particles . . . You're correct that the illumination function should not be global for whole ring system. I will fix this, and it's actually not all that processor intensive, particularly on GeForce and Radeon graphics cards that have programmable lighting engines.

3) I get a strange 'winking' effect concerning the brightness of planets from a distance. To reproduce: move ~35AU away from the sol, centre on sol, and rotate around it. The planets wink on and off (or discontinuously to mid-brightness) rather then waxing and waning smoothly. Might this be related to my display problems in the previous post? This winking behaviour does not happen in 124.

I just fixed that this afternoon, along with the 'squareness' of planets and moons seen from a distance.

4) Not a bug report but a quiery: earlier, Chris, you suggested that it would be possible in the future to adjust the distance or angular size before orbits were rendered. Is this feature/hack available now?

You can do this in 1.2.4 and later . . . Modify the start.cel script and add the line:

set { name "MinOrbitSize" value "20" }

The value is specified in pixels . . .

--Chris


Hate being this picky... but Celestia's so near to perfect that it makes a pedant out of me.
[/quote]

[jrobert]

In 124, the readme file indicates that clicking the mouse wheel resets the FOV (Field Of View) to 45 degrees. However when the mouse wheel is clicked, nothing happens and the only way I can truely reset the FOV is to exit out of the entire program and restart it.

PS: Pentium 4 1.6Ghz, 512MB, nVidia Geforce2 GTS 32MB DDR, Microsoft Wheel Mouse Optical USB.. (dunno if that'll help any)

[chris]

In 124, the readme file indicates that clicking the mouse wheel resets the FOV (Field Of View) to 45 degrees. However when the mouse wheel is clicked, nothing happens and the only way I can truely reset the FOV is to exit out of the entire program and restart it.

PS: Pentium 4 1.6Ghz, 512MB, nVidia Geforce2 GTS 32MB DDR, Microsoft Wheel Mouse Optical USB.. (dunno if that'll help any)

This feature was in early versions of Celestia and then was accidentally left out. It will reappear in 1.2.5 (next prerelease, actually) in a slightly more useful form: pressing the middle mouse button (usually the mouse wheel) will toggle between 45 degrees and your last field of view. Thanks to t00fri for implementing this.

--Chris

[HankR]

Re the direction of comet tails, my understanding is that Type I (ion) tails are generally straight and point almost directly away from the sun, trailing the radius vector (from the sun to the nucleus) by just a few degrees.

- Hank

[Buzz]

Corrrect me if I'm wrong, but I thought that one tail is composed of neutral particles and is directed away from the sun, and the other tail made of charged particles is affected by magnetic fields.

[HankR]

You are correct that there are two types of tails. However, the ionized (charged) tail is the one that is directed away from the sun, because it is mobilized by the solar wind which flows outward from the sun. The neutral tail consists of dust particles which are unaffected by the solar wind. These particles move under the influence of solar gravity and light pressure. These particles are basically in solar orbit like the comet, but light pressure causes them to move outward from the comet's orbit, where gravity causes them to move more slowly than the comet. This results in a tail curving away from the comet.

- Hank