Hi,
Am 15.11.2011 um 23:10 schrieb Robert Hanson:
> Oh, you mean you were able to direct the fog from the back to the front?
> That's an idea....
>
> ...nope. I can't get it to work. I think it's a POV-Ray bug. Do you suppose
> they never considered using ground fog this way?
>
me neither, so searched some more
The last two entries claim it works?!
http://news.povray.org/povray.general/thread/%[email protected]%3E/?ttop=227500&toff=900
There is also an entry in the PyMOL list suggesting it works:
http://www.mail-archive.com/[email protected]/msg00850.html
They use another approach (an object whose interior fade to some color, they
use a plane but I also tried it with a box):
http://www.dino3d.org/pov/index.php?p=depth
I tried the 'dino' approach, but yet again I couldn't make it work :-(
See also: http://www.povray.org/documentation/view/3.6.0/410/ and
http://www.povray.org/documentation/view/3.6.1/416/
However, I sort of faked the effect using multiple planes which transmit less
and less light.
background { color rgb <0,0,0> }
plane{ z, 5000
texture { pigment { color rgbft <0,0,0,1,0.8> } }
}
plane{ z, 5050
texture { pigment { color rgbft <0,0,0,1,0.7> } }
}
plane{ z, 5100
texture { pigment { color rgbft <0,0,0,1,0.6> } }
}
Though this fails for a white background...
I have the feeling I am missing something.
Best
Alex
> On Tue, Nov 15, 2011 at 10:29 AM, Alexander Rose
> <[email protected]> wrote:
> Hi Bob,
>
> I agree to what you said regarding fog_type=1, but why do you think the
> ground fog (fog_type=2) is not a solution? It's not just ground fog but fog
> along the up vector.
>
> So my idea was that with an up vector that points in the same direction as
> the vector from the camera location to the 'look_at' point you would get is
> very, very weak up to some point where it has a high constant value. My
> understanding is, that you could achive this when you set distance so that
> the fog is generally very weak; set fog_offset so that the fog hides the
> protein at the desired location; set fog_alt to adjust how fast the fog hides
> the protein. But then again, I was not able to get the desired results...
>
> Alexander
>
> fog {
> distance 1
> color rgbft <0,0,0,0.0,0.0>
> fog_type 2
> up <0,0,1>
> fog_offset ZCoordinateOfProteinCenter /* Constant below this */
> fog_alt 0.5 /* Decay rate */
> }
>
>
> ----- Ursprüngliche Mail -----
> > Von: "Robert Hanson" <[email protected]>
> > An: [email protected]
> > Gesendet: Dienstag, 15. November 2011 16:02:57
> > Betreff: Re: [Jmol-users] fog/zShade in POV-Ray
> > Well, after a bit of experimentation, I'd say this is probably not
> > going to work. POV-Ray assumes that you are IN the fog yourself,
> > looking around. So everything in a scene is foggy. There is no way
> > around that. Certainly fog_type=2 (ground fog) is not a solution.
> >
> > Jmol uses a very different idea -- you are looking at the model, and
> > it is partially obscurred by fog. This is much more dramatic, and much
> > more useful. The key setting is zSlab, which is assumed to be about
> > 300 in POV-Ray but is critically important to be around 50 for Jmol.
> > (I just checked in a bug fix that was setting zSlab to 0 by default in
> > Jmol.)
> >
> > If you want something that is about the same in both, try this:
> >
> > in Jmol:
> >
> > background white
> > set zSlab 300
> > set zDepth -1000
> > set zShadePower 3
> > set zShade
> >
> > Then in POV-Ray use:
> >
> > fog {
> > distance 1500
> > color rgb <1,1,1>
> > fog_type 1
> > }
> >
> >
> >
> > Bob
> >
> >
> > ps. For the record....
> >
> > The algorithm for fog in Jmol is this, applied to each pixel:
> >
> > f = (zDepth - z) / (zDepth - zSlab) // fraction of depth, from zDepth
> > (0) to zSlab(1)
> >
> > p = f^zShadePower // default: f^3
> >
> > pixel_color = background_color + p * (object_color - background_color)
> >
> > = p * object_color + (1 - p) * background_color
> >
> > Comparing that to POV-Ray:
> >
> > PIXEL_COLOR = exp(-d/D) * OBJECT_COLOR + (1-exp(-d/D)) * FOG_COLOR
> >
> > where d is the pixel depth from the camera and D is the "fog distance
> > parameter"
> >
> > Note that these would be identical if
> >
> > FOG_COLOR = background_color
> > p = exp(-d/D)
> >
> > Of course, that's not what p is. The main difference here is that it
> > is quite possible in Jmol to have an object disappear. That is
> > intentional. In Jmol, we absolutely allow that, for good reason -- for
> > good effect. zShadePower was developed for the infinite crystal view
> > in the Epcot Touch-A-Molecule display. We need that, because we only
> > have a certain number of unit cells in actuality, and it is very
> > effective. In contrast, it's not possible in POV-Ray to get full
> > merging with background color, probably because that is more
> > realistic, and the POV-Ray formula results in the color being 1/e of
> > pixel_color "at depth" (0.368) instead of 0 * pixel_color, as in Jmol.
> >
> > Both of these algorithms result in a fog that gets stronger further
> > from you, allowing objects closer to the viewer to be less affected
> > than distant objects. The power of that effect is more adjustable in
> > Jmol than in POV-Ray, and the formula is different, because I needed
> > full disappearance within a finite distance, which I suppose is not
> > realistic so is not modeled by POV-Ray, and I needed to have the
> > observer and possibly part of the model outside of the fog.
> >
> >
> >
> >
> > --
> > Robert M. Hanson
> > Professor of Chemistry
> > St. Olaf College
> > 1520 St. Olaf Ave.
> > Northfield, MN 55057
> > http://www.stolaf.edu/people/hansonr
> > phone: 507-786-3107
> >
> >
> > If nature does not answer first what we want,
> > it is better to take what answer we get.
> >
> > -- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
> >
> > ------------------------------------------------------------------------------
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> > https://lists.sourceforge.net/lists/listinfo/jmol-users
>
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>
>
> --
> Robert M. Hanson
> Professor of Chemistry
> St. Olaf College
> 1520 St. Olaf Ave.
> Northfield, MN 55057
> http://www.stolaf.edu/people/hansonr
> phone: 507-786-3107
>
>
> If nature does not answer first what we want,
> it is better to take what answer we get.
>
> -- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
> ------------------------------------------------------------------------------
> RSA(R) Conference 2012
> Save $700 by Nov 18
> Register now
> http://p.sf.net/sfu/rsa-sfdev2dev1_______________________________________________
> Jmol-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/jmol-users
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