|
|
|
|
|
|
| |
| |
|
|
From: Wolfgang Wieser
Subject: Re: (simple?) Isosurface patch request
Date: 14 Aug 2004 14:23:29
Message: <411e58a0@news.povray.org>
|
|
|
| |
| |
|
|
Samuel Benge wrote:
> I understand this. But if we *can* get bevelled edges using higher
> accuracy values, why not let people use it that way?
>
Well... it would (again) be some sort of "art produced by numerical
errors in the solver".
I certainly won't keep you from doing such things and it's great if
it works for you.
However, don't yell at us if things break in the next version. Numerical
algorithms typically give results which are only exact up to some certain
error (i.e. accuracy). And it is no good idea to rely on a special behaviour
of the numerical error.
>> (3) It does greatly improve the actual surface accuracy. While the current
>> code will have the real root depth within the specified accuracy, the
>> patched code will have it within 1/10 to 1/100 (typ.) of the accuracy.
>> This in turn means, that one can render equally-well images with smaller
>> accuracy and hece faster. See below, too.
>
> This is what's really frustrating me.... I know the patch is better when
> it comes to accuracy. With the 'official' isosurface, we have to use
> accuracy values which are MUCH SMALLER than the needed 'grain size', or
> resolution of the isosurface to rid ourselves of the black dots.
>
The actual accuracy improvement depends on the function used.
It seems you did not completely understand the grain size argument.
If you look at the isosurface (mathematically!) of a function, this can be
very smooth (like a billard ball) strongly grainy (like a sponge).
In order to get a useful representation of the isosurface, you normally
need an accuracy value which is smaller than the characteristic grain
size. This is necessary to make sure that the first root along the
light ray is actually found (and not any root). This is independent of
my patch.
landscape), are very smooth and hence the "grain size" is large and
you could use a fairly large accuracy value. So, here we find the correct
(i.e. first) root easily but the result for the ray depth of the root may
be displaced from the real location by the amount of accuracy. And here
comes the patch: By linearly interpolating, this guess for the actual
location of the root between the last two evaluation points can be
"greatly" improved.
How much depends on the function used. For very smooth functions
(especially the mars topo which is itself a linearly interpolated function),
you can gain the mentiones factor 10 to 100. For other less smooth
functions it will be less and for really rough ones we won't win anything
but also not lose anything.
> Can I give you an example isosurface statement, to test my theory on
> this? I've seen the problems; I believe your patch fixes them. If we
> break even on render time, so be it. A fix is a fix.
>
Well, feel free to post or send me the SDL code in question. I'll give it a
run (unless it takes ages :).
> *Sigh* I wish I knew how to compile POV's source code... :c/
>
tar xfj povray-3.6.1.tar.bz2
./configure COMPILED_BY=your_name
make
Wolfgang
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Christoph Hormann wrote:
> Samuel Benge wrote:
>
>>
>> This is what's really frustrating me.... I know the patch is better
>> when it comes to accuracy. With the 'official' isosurface, we have to
>> use accuracy values which are MUCH SMALLER than the needed 'grain
>> size', or resolution of the isosurface to rid ourselves of the black
>> dots.
>>
>
> You should really better show an example. Black dots are nearly always
> an indication of unsuccessful root finding and then this patch would not
> help as explained.
>
> Christoph
Okay, the example image has been uploaded to p.b.i. I gave three
examples in png format, each one having a different accuracy value.
Also, the isosurface has smooth and rough surfaces combined for obvious
reasons. The code for the example is below. You might want to uncomment
the max_gradient and use very high values, to conclude the artifacts
shown are not related to max_gradient. Also, I encourage both you and
Wolgang to try this in the patched version. I'd like to see the results.
-Sam
// Begin Code
global_settings{
assumed_gamma 1
}
#default{ finish{ ambient 0 } }
camera{
fisheye
right x*.5 up y*.5
//right x*.5*1.33 up y*.5
location< 0, 20, -30 >
look_at 0
angle 14
}
background{ rgb<.3 .4 .5> }
light_source{<1,2,-.95>*100000,<1 1 .8>*2 }
#declare tex=
function{
pattern{
granite
}
}
isosurface {
function{
min(
max( // cube
abs(x),
abs(y),
abs(z)
)-1,
max(
sqrt(y*y+z*z)-.75, // cylinder
abs(x)-2
)+tex(x,y,z)/10 // rough surface
)
}
accuracy .05 // .01 // .001
//max_gradient 100
evaluate 0.6, 1.8, 0.95
contained_by{
box{
<-2.1,-1.1,-1.1>,
<2.1,1.1,1.1>
}
}
pigment{ rgb 1 }
rotate y*35
}
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Samuel Benge wrote:
>
> Okay, the example image has been uploaded to p.b.i. I gave three
> examples in png format, each one having a different accuracy value.
> Also, the isosurface has smooth and rough surfaces combined for obvious
> reasons. The code for the example is below. You might want to uncomment
> the max_gradient and use very high values, to conclude the artifacts
> shown are not related to max_gradient. Also, I encourage both you and
> Wolgang to try this in the patched version. I'd like to see the results.
>
What you see on the front face of the box are exactly the explained
shadow ray noise effects you also see on Wolfgang's samples caused by
tangential lighting. The surface is always found reliably, just if it
is in shadow or not varies. Since these surfaces result from a
precisely linear function the linear interpolation leads to perfect
results here for arbitrary accuracy values (on the faces, not near the
edges and only within the accuracy of floating point numbers of course).
Since you usually won't use tangential lighting in real scenes for such
flat surfaces i moved the light source a bit. I also changed
max_gradient to 4 (the real maximum gradient of the function seems just
above 3). Here are the results:
no interpolation:
http://www.tu-bs.de/~y0013390/files/sam_test1_o05.png
http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
http://www.tu-bs.de/~y0013390/files/sam_test1_o001.png
with Wolfgang's patch:
http://www.tu-bs.de/~y0013390/files/sam_test1_i05.png
http://www.tu-bs.de/~y0013390/files/sam_test1_i01.png
http://www.tu-bs.de/~y0013390/files/sam_test1_i001.png
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 06 Jul. 2004 _____./\/^>_*_<^\/\.______
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Christoph Hormann wrote:
>What you see on the front face of the box are exactly the explained
>shadow ray noise effects you also see on Wolfgang's samples caused by
>tangential lighting. The surface is always found reliably, just if it
>is in shadow or not varies. Since these surfaces result from a
>precisely linear function the linear interpolation leads to perfect
>results here for arbitrary accuracy values (on the faces, not near the
>edges and only within the accuracy of floating point numbers of >course).
>Since you usually won't use tangential lighting in real scenes for
such >flat surfaces i moved the light source a bit.
Umm, I see this a lot, actually. The more complex a shape becomes, the
more these 'tangental lighting' artifacts appear. They happen on curved
surfaces, too, but with less obvious striation. I hate having to move my
light_source so often, but at least it's a fix for the flat surfaces...
>I also changed max_gradient to 4 (the real maximum gradient of the
>function seems just above 3). Here are the results:
>no interpolation:
>http://www.tu-bs.de/~y0013390/files/sam_test1_o05.png
>http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
>http://www.tu-bs.de/~y0013390/files/sam_test1_o001.png
>with Wolfgang's patch:
>http://www.tu-bs.de/~y0013390/files/sam_test1_i05.png
>http://www.tu-bs.de/~y0013390/files/sam_test1_i01.png
>http://www.tu-bs.de/~y0013390/files/sam_test1_i001.png
>Christoph
Wow. Those results look encouraging. It's much like I suspected: edges
no longer have that jagged look. The chopped-up surface is now smooth.
Some spots still appear, though. I'm sure in time all such artifacts
will be resolved.
Have you tried both patches (yours and Wolfgang's) combined yet? With AA?
-Sam
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Samuel Benge wrote:
>
> Wow. Those results look encouraging. It's much like I suspected: edges
> no longer have that jagged look. The chopped-up surface is now smooth.
> Some spots still appear, though. I'm sure in time all such artifacts
> will be resolved.
???
To me the difference seems very minor, not even close to 10x the
accuracy value leading to the same result quality.
Just in case this was not clear: the 'i' samples are with the patch, the
'o' ones without (like with official POV-Ray 3.6).
> Have you tried both patches (yours and Wolfgang's) combined yet? With AA?
What patch of mine are you referring to? The isosurface bounding tree
patch has nothing to do with this.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 06 Jul. 2004 _____./\/^>_*_<^\/\.______
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Christoph Hormann wrote:
> Samuel Benge wrote:
>
>>
>> Wow. Those results look encouraging. It's much like I suspected: edges
>> no longer have that jagged look. The chopped-up surface is now smooth.
>> Some spots still appear, though. I'm sure in time all such artifacts
>> will be resolved.
>
>
> ???
>
> To me the difference seems very minor, not even close to 10x the
> accuracy value leading to the same result quality.
That's because you seem to be bent on using really low accuracy
settings, or something. All I'm implying is that it's not necessary to
use such low accuracy values all the time... it actually seems 'safe'
not to now, with the new patch.
> Just in case this was not clear: the 'i' samples are with the patch, the
> 'o' ones without (like with official POV-Ray 3.6).
It was clear, thanks.
>> Have you tried both patches (yours and Wolfgang's) combined yet? With AA?
>
>
> What patch of mine are you referring to? The isosurface bounding tree
> patch has nothing to do with this.
>
> Christoph
I guess if you believe linear interpolation patch won't help speed up
isosurface rendering significantly, you might say that.
-Sam
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Samuel Benge wrote:
>
> I guess if you believe (the) linear interpolation patch won't help speed up
> isosurface rendering
>
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Samuel Benge wrote:
>>
>> To me the difference seems very minor, not even close to 10x the
>> accuracy value leading to the same result quality.
>
> That's because you seem to be bent on using really low accuracy
> settings, or something. All I'm implying is that it's not necessary to
> use such low accuracy values all the time... it actually seems 'safe'
> not to now, with the new patch.
I have no idea how you come to this conclusion, to me
http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
looks much better than:
http://www.tu-bs.de/~y0013390/files/sam_test1_i05.png
and it only uses 5 times the accuracy value. I am using exactly the
accuracy values you proposed (x05 meaning accuracy 0.05).
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 06 Jul. 2004 _____./\/^>_*_<^\/\.______
Post a reply to this message
|
|
| |
| |
|
|
From: Wolfgang Wieser
Subject: Re: (simple?) Isosurface patch request
Date: 14 Aug 2004 17:52:18
Message: <411e8991@news.povray.org>
|
|
|
| |
| |
|
|
Christoph Hormann wrote:
> with Wolfgang's patch:
>
It's nice to see that you're actually using it (sometimes at least) ;))
Wolfgang
Post a reply to this message
|
|
| |
| |
|
|
From: Wolfgang Wieser
Subject: Re: (simple?) Isosurface patch request
Date: 14 Aug 2004 18:02:40
Message: <411e8bff@news.povray.org>
|
|
|
| |
| |
|
|
Christoph Hormann wrote:
> I have no idea how you come to this conclusion, to me
>
> http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
>
> looks much better than:
>
> http://www.tu-bs.de/~y0013390/files/sam_test1_i05.png
>
...but
http://www.tu-bs.de/~y0013390/files/sam_test1_i01.png
looks better than
http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
doesn't it?
BTW, we're not talking about what _looks_ better but what matches
the actual surface better.
I'm saying this because of the different looks of the grainy cylinder.
Seems the grain size is in the order of the accuracy.
>Since you usually won't use tangential lighting in real scenes for such
>flat surfaces
>
Well, I think this argument won't help. Imagine an animation where
the object is moved relative to the light (rotation e.g.)...
When I think that we would not have all that discussion if R. Suzuki had
thought of the linear interpolation himself, then it's probably a good time
to say good night and go to bed... :)
Wolfgang
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
|
|