Reactor wrote:
> I'd have to see an example, but what you've described sounds kind of like
> sampling artifacts  Is the second sampling parameter still used with method 3?
> try boosting the min samples to 50 and rendering only that small part of the
> scene.  If it is closer to what you expected, then it was caused by sampling
> errors.
> 
> -Reactor


That helps, but it causes the scene to take a real long time to render. 
Would splitting into multiple objects help?

-Mike

Post a reply to this message

> SharkD <mik### [at] gmailcom> wrote:
>> Reactor wrote:
>>> You can try increasing the extinction value in the scattering block.  By
>>> default, extinction is 1.0, but you can increase it to something higher to
>>> increase the amount of light absorbed by the media without actually thickening
>>> the media.  By doing this, though, your clouds may have a very strong color
>>> contrast with white at the tops and a very dark bottom.  You can control the
>>> contrast of the clouds by balancing the scattering media with absorption and
>>> emission medias.
>>>
>>>
>>> -Reactor
>> Thanks! Any tips on the increasing brightness problem I described in my
>> other post?
>>
>> -Mike
> 
> I'd have to see an example, but what you've described sounds kind of like
> sampling artifacts  Is the second sampling parameter still used with method 3?
> try boosting the min samples to 50 and rendering only that small part of the
> scene.  If it is closer to what you expected, then it was caused by sampling
> errors.
> 
> -Reactor
> 
> 

Is the second sampling parameter still used with method 3?
No!
There is no longer a concept of min and max samples. Only samples.

Do I need to change the number of intervals?
NO! Leave it at 1. Otherwise, it's slow like thick molace in winter. It 
can also cause artefacts. Increase the number of samples.


Alain

Post a reply to this message

SharkD <mik### [at] gmailcom> wrote:
> Reactor wrote:
> > I'd have to see an example, but what you've described sounds kind of like
> > sampling artifacts  Is the second sampling parameter still used with method 3?
> > try boosting the min samples to 50 and rendering only that small part of the
> > scene.  If it is closer to what you expected, then it was caused by sampling
> > errors.
> >
> > -Reactor
>
>
> That helps, but it causes the scene to take a real long time to render.

Yeah, scattering media does that.

> Would splitting into multiple objects help?

Probably not, unless you fit the media more tightly to the container shapes.
However, you could split it into multiple container shapes and use different
settings for those (if you wanted to).

-Reactor

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:

> Is the second sampling parameter still used with method 3?
> No!
> There is no longer a concept of min and max samples. Only samples.
>
> Do I need to change the number of intervals?
> NO! Leave it at 1. Otherwise, it's slow like thick molace in winter. It
> can also cause artefacts. Increase the number of samples.
>
>
> Alain


Ah, thanks.  I knew that about the intervals, but I wasn't sure about the
samples second parameter being ignored.  On a somewhat related note, I am
becoming increasingly curious as to how his image will look.

-Reactor

Post a reply to this message

Reactor wrote:
> SharkD <mik### [at] gmailcom> wrote:
>> Reactor wrote:
>>> You can try increasing the extinction value in the scattering block.  By
>>> default, extinction is 1.0, but you can increase it to something higher to
>>> increase the amount of light absorbed by the media without actually thickening
>>> the media.  By doing this, though, your clouds may have a very strong color
>>> contrast with white at the tops and a very dark bottom.  You can control the
>>> contrast of the clouds by balancing the scattering media with absorption and
>>> emission medias.
>>>
>>>
>>> -Reactor
>> Thanks! Any tips on the increasing brightness problem I described in my
>> other post?
>>
>> -Mike
> 
> I'd have to see an example, but what you've described sounds kind of like
> sampling artifacts  Is the second sampling parameter still used with method 3?
> try boosting the min samples to 50 and rendering only that small part of the
> scene.  If it is closer to what you expected, then it was caused by sampling
> errors.
> 
> -Reactor
> 
> 

Here's an example:

http://i421.photobucket.com/albums/pp292/SharkD2161/Support/gh_scene_outdoors_cubemap.png

Notice how the clouds are darker near the camera (at the top of the 
image) and get lighter the farther away they are (toward the middle of 
the image). The samples are already set pretty high:

samples 30, 100

-Mike

Post a reply to this message

SharkD schrieb:
> Notice how the clouds are darker near the camera (at the top of the 
> image) and get lighter the farther away they are (toward the middle of 
> the image). The samples are already set pretty high:

It appears to me they're much too thinned-out. So you get that bright 
white far off where the ray hits shallow enough to traverse a 
considerable distance in the clouds, but almost plain blue sky right above.

Also note that in reality, the far-off clouds would be hit at a less 
shallow angle due to earth's curvature; maybe you can achieve a similar 
effect by very slightly tilting the sky. Alternatively, you could use a 
shell made out of actual gigantic spheres as your media container (you 
may need to adjust your density pattern in that case though).

Another thing that looks weird is the apparent "stacking" - hard to tell 
where that comes from. Maybe the geometry is way different from what I 
think it is.

Post a reply to this message

Thanks for taking a look!

clipka wrote:
> It appears to me they're much too thinned-out. So you get that bright 
> white far off where the ray hits shallow enough to traverse a 
> considerable distance in the clouds, but almost plain blue sky right above.

I'll try fattening the layer up a little.

> Also note that in reality, the far-off clouds would be hit at a less 
> shallow angle due to earth's curvature; maybe you can achieve a similar 
> effect by very slightly tilting the sky. Alternatively, you could use a 
> shell made out of actual gigantic spheres as your media container (you 
> may need to adjust your density pattern in that case though).

Yes, but precision errors occur if I make the spheres *too* big. How big 
would be big enough? In my scene 1 unit = 1 meter.

> Another thing that looks weird is the apparent "stacking" - hard to tell 
> where that comes from. Maybe the geometry is way different from what I 
> think it is.

Not sure what you mean by "stacking".

Thanks again!

-Mike

Post a reply to this message

SharkD schrieb:
> Yes, but precision errors occur if I make the spheres *too* big. How big 
> would be big enough? In my scene 1 unit = 1 meter.

Don't worry about precision issues.

For exact scale, the atmosphere should have a radius of some 6e+6 units, 
which is indeed comparatively close to the distance limit at which 
objects disappear; still, it's within that limit. Also note that this 
distance cut-off is /relative/ to a ray's origin (e.g. the camera), and 
with an atmosphere thickness of just a few 1000 units and the camera 
just a few units away from the ground, you'll only be able to see a 
small section of the atmosphere anyway. Somewhere between 1e+5 and 1e+6 
units I'd guesstimate - dunno.

Bounding is no issue either: You'd be inside the sphere anyway, so the 
bounding box will be intersected anyway, so even if it is of low 
precision or turned off entirely, that doesn't make a difference.

And don't worry either about possible loss of details due to the center 
of the atmosphere being quite far away from your details: As POV-Ray 
uses double-precision math, a scene encompassing the whole earth would 
still allow headroom for details as small as a nanometer(!), so there 
should be enough headroom.


Make sure though to center your area of interest at <0,0,0>, so don't 
make that the center of your atmosphere.

>> Another thing that looks weird is the apparent "stacking" - hard to 
>> tell where that comes from. Maybe the geometry is way different from 
>> what I think it is.
> 
> Not sure what you mean by "stacking".

Well, the clouds look somewhat like the closer(?) ones are thinned-out 
copies of the further-off(?) ones. Or as if they were actually as far 
off as what they appear to be copying, just higher.

Post a reply to this message

clipka wrote:
> SharkD schrieb:
>> Yes, but precision errors occur if I make the spheres *too* big. How 
>> big would be big enough? In my scene 1 unit = 1 meter.
> 
> Don't worry about precision issues.
> 
> For exact scale, the atmosphere should have a radius of some 6e+6 units, 
> which is indeed comparatively close to the distance limit at which 
> objects disappear; still, it's within that limit. Also note that this 
> distance cut-off is /relative/ to a ray's origin (e.g. the camera), and 
> with an atmosphere thickness of just a few 1000 units and the camera 
> just a few units away from the ground, you'll only be able to see a 
> small section of the atmosphere anyway. Somewhere between 1e+5 and 1e+6 
> units I'd guesstimate - dunno.

Correction, I just double-checked and 4 units = 1 meter. I hope that 
doesn't affect anything.

-Mike

Post a reply to this message

> Thank you very much . I like read your post
> <a href="http://nganhangonline.com"> ngan hang viet nam  </a>
>
> http://www.nganhangonline.com
>

Post a reply to this message