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I was intrigued by the fact that an entire apple could be described by a
parametic equation: (WAY down at the bottom of the page)
http://www.econym.demon.co.uk/isotut/printable.htm
I wanted to play around with this some, but naturally it's been so long that I
have to RElearn how to get my brain to play nicely with functions.
#declare Apple = parametric {
function { cos(u) * (R1 + R2*cos(v)) + pow((v/pi), 100) },
function { sin(u) * (R1 + R2*cos(v)) + 0.25 * cos(5*u) },
function { -2.3 * ln(1 - v*0.3157) + 6*sin(v) + 2*cos(v) }
<0,0>, <2*pi,pi>
contained_by { sphere{0, 1.1} }
max_gradient 10
accuracy 0.0001
precompute 10 x,y,z
texture {pigment {color Red}}
}
This is throwing a
Parse Error: Expected 'parameter identifier or floating-point constant
identifier', } found instead
at the first _function_ line.
This leads me to believe that I'm missing something, but I've searched and read
things and looked at examples all over the place but haven't been able to lay my
finger on what's causing the error.
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Ok, the error was caused by a typo in defining R1, but now when the script runs,
there's no object visible.
I'm assuming I'll have to play with the following values, but I find it starnge
that I get NOTHING.
contained_by { sphere{0, 2} }
max_gradient 5
Not a dark spot, just... nothing.
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> Ok, the error was caused by a typo in defining R1, but now when the script runs,
> there's no object visible.
>
> I'm assuming I'll have to play with the following values, but I find it starnge
> that I get NOTHING.
>
> contained_by { sphere{0, 2} }
> max_gradient 5
>
> Not a dark spot, just... nothing.
>
>
Look at the messages after the render. Does it say anything about
max_gradient?
As one of the functions contain pow((v/pi), 100), the effective
max_gradient may be rather large. Try using max_gradient 100 or more.
Did you actualy /place/ your Apple object?
Add:
object{Apple pigment{rgb<1,0,0>}}
To your scene.
Alain
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> Look at the messages after the render. Does it say anything about
> max_gradient?
Nope.
But it did helpfully tell me what I might need to solve the issue:
Ray->Shape Intersection Tests Succeeded Percentage
Parametric 96390 0 0.00
Parametric Bound 245308 96390 39.29
Bounding Box 571708 490616 85.82
> Did you actualy /place/ your Apple object?
> Add:
> object{Apple pigment{rgb<1,0,0>}}
> To your scene.
Yep!
I did manage to do that. I even had the computer plugged in when running the
render. :D Yay for me!!!
object {Apple scale 10 texture {pigment {color Red}}}
(I thought maybe I just couldn't see it, so I kept scaling it up, and stopped at
10) So, bigger bounded_by, and smaller scale - to keep the render time down?
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Changing to :
contained_by { sphere{0, 1.1} }
max_gradient 30
accuracy 0.1
Gave me a red sphere after 5 min.
(using object {Apple scale 1 texture {pigment {color Red}}} )
camera {location <0.0, 0.0, -10.0> look_at <0, 0, 0>}
Message window:
Ray->Shape Intersection Tests Succeeded Percentage
Parametric 32428 18225 56.20
Parametric Bound 37710 32428 85.99
Bounding Box 387070 75420 19.48
Function VM calls: 281215195
I'm unsure how to interpret this output. Do I need to increase my contained_by
size to 1.28 (1.1/0.86)? Or do I need to double it because Parametric
Percentage is down near 50%?
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On 07/21/2014 10:15 AM, Bald Eagle wrote:
> Changing to :
>
> contained_by { sphere{0, 1.1} }
> max_gradient 30
> accuracy 0.1
>
> Gave me a red sphere after 5 min.
>
Have your tried working from the source code Mike provides via
download-able zip at the bottom of the page:
http://www.econym.demon.co.uk/isotut/real.htm ?
His Apple.pov example works without trouble for me in < 15 seconds. No
AA at default povray resolution.
Bill P.
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> Have your tried working from the source code Mike provides via
> download-able zip at the bottom of the page:
> http://www.econym.demon.co.uk/isotut/real.htm ?
Ooooooh. Tricksy you are, reading all the way down to the bottom of the page.
Stupid I was feeling, when I discovered that zip file already on my hard drive.
:(
I am, however, ever so grateful.
You've denied me my cross of agony and frustration.
> His Apple.pov example works without trouble for me in < 15 seconds. No
> AA at default povray resolution.
Wicked cool. I, embracing the technology of The Ancients, am able to render it
in a mere 1:52. (4:27 with aa).
Thanks for the tip, WP! While that gets me an amazing apple (really? with only
TWO pigments??), I'm still just as ignorant about the ray ---> intersection
output. I also didn't see any notification in the message window about
max_gradient. Is it there? Nothing leapt off the screen, grabbed me around the
neck, and screamed, "LOOK AT ME!!!" So I may have missed it. :O
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On 07/21/2014 09:47 PM, Bald Eagle wrote:
>
> Wicked cool. I, embracing the technology of The Ancients, am able to render it
> in a mere 1:52. (4:27 with aa).
Suppose with ray tracing as in the movie Jaws, once you see the shark,
you want a bigger boat. ;-)
>
> Thanks for the tip, WP! While that gets me an amazing apple (really? with only
> TWO pigments??), I'm still just as ignorant about the ray ---> intersection
> output. I also didn't see any notification in the message window about
> max_gradient. Is it there? Nothing leapt off the screen, grabbed me around the
> neck, and screamed, "LOOK AT ME!!!" So I may have missed it. :O
>
I admit to not spending much time with the intersection test values
beyond checking them for sanity if I am getting a result which is
completely wrong. That said, I believe what gets reported is basically a
hierarchy of tests. How many rays hit the bounding box(es) -> how many
of those rays hit the parametric containing sphere -> finally how many
of those rays hit the parametric object.
As for a maximum gradient report. I re-ran Mike's example code
commenting out the precompute option and adding a max_gradient of 0.5.
Only a portion of the object renders, so I would expect to see a max
gradient report - if they are reported for parametric objects - but I do
not. Lastly looking at the source code for the parametric object, it
doesn't look to me like any attempt is made to record and report a max
gradient as is the case with isosurfaces.
Bill P.
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Thanks for taking a look at that, it would have bothered me for a while.
After reading various threads on the explanation of why parametrics are so slow
to render, and how there can be problems seeing where the surface is supposed to
be rendered, I decided to see how fast the equations could be plotted out if I
"manually" ran through values of phi and theta. I figured this would also be
independent of any reliance on contained_by shapes, and would help rapidly
troubleshoot parametrics.
of note: I started out trying use "functions", and after contemplating
POV-i-cide, decided to just declare equations and while-loop through them.
Results at:
http://news.povray.org/povray.binaries.images/thread/<web.53cec54fc9bb24105e7df57c0%40news.povray.org>/
Even with the frequency (2 radians) and the bells and whistles, it renders for
me at +q9 in 25 sec.
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