Triangles in the sky

[PabloMack]

I have a dusk scene in which TG is generating tending toward sky blue triangles in the sky centered on the horizon. I've seen other similar posts. Mine seem to be somewhat near the antipole from sun which is probably just below the horizon and off to the back of the viewer's right shoulder. Upping the render detail makes them smaller but they don't go away at 0.5 or even 0.75. In an animation, they dance around and the pattern makes its way from the right edge of the view to the left as the sun gets lower. The pattern is still visible even as it goes behind the house but shapes are more rounded and blurred. In the video the sun is animated and goes from an inclination of +2 (at the beginning) to -2 (at the end).

[attach=1]
https://www.youtube.com/watch?v=7Ge8k_gcHow

[PabloMack]

I just discovered the cause. I have a "street light" source in the scene that goes from right to left in front of the camera as the camera moves to the right and pans to the left to keep the house centered in the view. The triangles are centered around the light but they form a pattern of these aberrations to a significant diameter around the light source. Is this normal/expected? I suppose I could put the "street light" farther away so that it does not go in front of the camera but I will have to strengthen it considerably. Below is a Preview Render showing the light source bounding box in white:

[attach=1]

[Upon Infinity]

I suspect it has to do with a quality tab somewhere.  Perhaps in the atmosphere shader...

[Oshyan]

There are sometimes issues with noise around localized light sources, but I've never seen it looking so much like large polygons. What are your atmosphere and main detail settings?

- Oshyan

[Dune]

Perhaps turning off everything but the light helps, I mean shadows, glow, and such.

[PabloMack]

Perhaps turning off everything but the light helps, I mean shadows, glow, and such.

I haven't tried turning those things off.

[Dune]

Shadows, specular... off may help, and distance is very high still; streetlamps won't get that far, though I'm not sure if changing that changes anything to the real distance, might just be depending on the strength.

[Oshyan]

Well, I immediately see the reason why the bright points (noise) are so large, it's the 0.25 detail, which I figured might be the case but it's definitely making it look a lot worse. The only way to fix it (or at least minimize it), if you choose to keep the localized light source, would be to either render with higher detail and atmosphere samples, or use Defer Atmo with moderate AA. If all you want is a sort of "fill light" coming from one direction, use a Sunlight instead; as an infinite light source it doesn't render with these same issues.

Edit: I can't say for sure without the other elements in your scene, but I think Defer Atmo is going to give you better results faster here because without it you have to increase Detail so much to reduce the size of the bright noise. Actually *reducing* the noise is a somewhat separate issue that will come with higher atmo samples (bith with Defer Atmo and without it).

- Oshyan

[PabloMack]

I rendered at Detail of .75 and still had the triangles, though smaller. It doesn't seem right that the triangles are noticeably larger than the detail from a comparable distance. The light is a street light that is supposed to be illuminating a house at night. A distant light would light up everything and that I don't want because it is supposed to be dusk. What I'll do is to just move the street light farther away so that it is behind the camera then I'll have to brighten it up to get the same amount of light shed on the subject.

[Oshyan]

You may end up with the same problem. You could try a Spot Light, see if it's any better, though I think it has similar issues. The way to fix it is to leave detail at maybe 0.5, but use Defer Atmo with AA of 6 or something, and keep atmo samples at maybe 64, I'd say. I haven't tested it, you'll have to experiment. But that will immediately make the noise much more fine-grained, even with lower AA (which would give you a similar *amount* of noise, but still finer-grained).

- Oshyan

[PabloMack]

I'll try these things out as time permits. Is AA short for "Anti-aliasing"?

[Kadri]

Martin tried some things that worked and i am not sure if these were the last ones about light problems.
But Pablo please have a look what Martin (Dandelo) said in these threads.
http://www.planetside.co.uk/forums/index.php/topic,9981.msg104094.html#msg104094
http://www.planetside.co.uk/forums/index.php/topic,16690.msg163081.html#msg163081

[Oshyan]

Yes, AA = anti aliasing.

- Oshyan

[PabloMack]

Anyhow, the long and short of it is; never use the current TG lightsources as a means to illuminate surroundings/atmosphere, just use luminosity.

That's a pretty strong statement. I remember a recent post where someone was trying to light an area with luminosity and they said they couldn't get enough light out of it even going to extreme numbers. If I need a misty effect then I'll have to remember this. The only problem is that you have to make sure that the source of luminosity is either wanted or not visible. That could be a challenge. Thanks Kadri for the links.

Moving the street lamp well out of frame and behind the camera did eliminate the triangles. My feeling is that such a light source is in the middle of an associated "sphere" where these artifacts are produced. Their severity is inversely related to the distance from the light source. When the air around a real light source is misty the light source causes the air to glow in the real world. In the TG world, I just have to remember that it causes glowing light triangles. I'll remember it this way: "If you don't want to end up with a cluster of moths (i.e. triangles) in your render then don't light the air with a street lamp that is in view because they attract moths!".  In an animation they even sort of looks like moths flying around a lamp.

[PabloMack]

Yes, AA = anti aliasing.

In another life AA once meant to me "Atomic Absorption" (for elemental analysis) or "Anti Aircraft" (as in flak).