Orbiter horizon curvature and other stuff

[Zachstar]

Bump, Spec, and more lights ought to be the primary goals of any DX9 or DX10 client.

But to be able to access the shader core gives you so much more.

Yes it becomes less of a use in space but what do you do in space? You travel, You don't spend as much time looking at space as you do staring at a control console or the time advance screen. Unless you are flying the shuttle which is an addon question and not an Orbiter one.

You spend your time looking on the ground. This is where shaders can make things FAR easier for the addon devs. It gives them so much freedom to add effects. Especially if they can spec if for sub 100 dollar modern cards like the 9600 and the HD 4670

 

[Hielor]

No, I don't think that this is the biggest cause. For planets in Orbiter, you can set the sphere detail (segments). Even if you set this to a high level, you will still see the curvature at altitudes where you wouldn't directly expect it at first. I still think it would be the same in reality when there was unlimited visibility.
The other effect you mentioned, only appears for non-spherical objects in Orbiter, not earth. Also consider that looking at the world in Orbiter would be the same as looking to the real world through a wide angle lens (depending on your FOV), which affects the curvature of the horizon depending on your attitude.

Actually, this is the case for earth. To test it, drive (on the surface of the ground, or using the scenario editor) away from Cape Canaveral about 30km. Turn around. In reality, the VAB would be partially below the horizon. In orbiter, you can see all of the VAB, and with the HUD on you can clearly see where the horizon is supposed to be (and thereby see what you shouldn't be able to see).

In other words, the planet is not where it seems to be. You can also see this by putting the camera slightly below the "ground" and noting that the textures are mapped to something that's still quite a ways below you.

(note that this will not be the case for surface tiles)

 

[cjp]

Just tested in orbiter at low altitude, and same effect visible: horizon gets pretty curved.
In fact, you can even reproduce something like the 2nd image I posted in realworld photography, while standing on the ground (using extreme wideangle or stiching).

I tried it myself:
Scenario: a standard KSC Delta Glider scenario (DG is on the runway)
FOV: 90 degrees (don't know how to make it larger)
Camera close to the DG

I could not make the horizon curved this way. The curvature was visible, but it was very small, and it was curved "down"(*) in all orientations. So, I think it's not related to projection distortions.

The most probable cause for the little bit of curvature I've seen is this:

In other words, the planet is not where it seems to be. You can also see this by putting the camera slightly below the "ground" and noting that the textures are mapped to something that's still quite a ways below you.

The reason for this is probably the Z-buffer range setting of the video card when the planet is being rendered. The entire planet has to fit within that range, and making its minimum distance too small would make it inaccurate.

Getting back to the original subject in the old thread: Flight Simulator does not have this issue. The problem can probably be solved by using multiple rendering steps for the surface rendering. Sounds like a nice job for OVP programmers.

(*) I mean the kind of curvature you'd expect at high altitudes.