Celestia Forums

Hi everyone:

For two years, I have been experiencing a bug on my P4 with Nvidia GeForce 4 TI 4200 video card, that apparently, many others are not experiencing. When I try to observe a cloud texture from under the cloud (below cloud ceiling), I will see a line of cloud along the horizon, but I can never get it to pass over my head. In other words, I can never see the cloud directly above me.

It makes no difference what cloud texture I am using (Don's or Fridgers or the VT textures).

The best way to see it is to view these images. They start at ground and rise in altitude. All six images are in the same spot. Notice that image 5 shows me just below the cloud layer and image 6 is just above (I set cloud height for this set of images at 12 km to give me some room).

Image 1 - near ground - notice the imfamous black horizon



Cloud 2 - 600 meters up. The cloud is at the horizon but not overhead



Cloud 3 - 1 km up. No real change



Cloud 4 - 8 km up - no real change



Cloud 5 - 11 km up - just below the cloud deck



Cloud 6 - 13 km up - above the cloud deck. Notice that the clouds below are quite thick and should be visible overhead when below the deck.



It is not the thinness of the clouds or thickness. This particular cloud set is the 16K VT textures, and there are places that are opaque thick. Even there, I cannot see any clouds overhead. It happens even with Fridger's 2k cloud texture.

Please help. I've been told this is not normal, and clouds should be visiable overhead when you are below them. Is this my particular video card? Do I have some settings wrong on it? Am I missing a shader or something? Whatever it is, it has been occurring through 5 video driver updates, in both 1.3.2 and 1.4.0 pre 6.

Edit Update: Clue! Clue! I have just discovered that I can see clouds overhead, but only between a zone of about 40 degrees N and 40 degrees South. It seems that the problem begins as a get away from the equator. I assume this has something to do with what Celestia does to wrap textures around spheres ... but ... Does that make any sense???


Help

Frank

Aha!

You must have Earth's "Oblateness" turned on!

It seems to be a bug in the "Oblateness" code.
I see a hole in the clouds when Oblateness is enabled, but no hole if it's disabled.

Earth's Oblateness is commented out in solarsys.ssc as it comes with Celestia. Most people wouldn't notice this particular effect since most don't edit solarsys.ssc.

It also seems to muck up the VT (at least level12) with oblateness on,Jestr

Selden, you're great. Oblateness was the problem. When I commented it out, I now have CLOUDS overhead everywhere!

THANKS

Frank

jestr wrote:It also seems to muck up the VT (at least level12) with oblateness on,Jestr

Yes, and the problem gets more noticeable the bigger the planet is. I discovered this when i was working on the VTs for the jovians in Ran; it turned out to be impossible to use deep VTs with oblateness on the bigger ones.

-rthorvald

The problem is that the code which renders virtual textures and clouds (its the same code) doesn't take into account oblateness. It seems a pretty straightforward fix to have it do that. Will look into this.

Oblateness?? why are you making Earth fat??
Sorry, couldn't resist.