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In article <38b53386@news.povray.org>, "Bill DeWitt"
<the### [at] earthlink net> wrote:
> Looks great how it is but you are right, just a little bit of
> texturing would go a long way on this. I am just baffled at how this
> is one IsoSurface! I suspect that there is some sort of a sin()/cos()
> thing going on, but dang if I can figger it.
>
> There is a -lot- more to IsoSurface than I will ever be able to learn.
function {
sqrt(
sqr(x)
+ sqr(y-sqrt(sqr(x/2)+sqr(z/2))*1.5)
+ sqr(z)
) - 1
- (sin(TH(x, y, z)*18)*0.1)//This is what makes the ridges
}
I will post the complete source in povray.text.scene-files after I clean
it up a little.
--
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/
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In article <38b54e72@news.povray.org>, "Mike Weber"
<mik### [at] pyxiscom> wrote:
> Outstanding!! Most realistic looking real-life thing. I think the
> thorns or pricks or whatever you want to call them is what makes it
> realistic - the randomness, as well as the soft shadows. Well done!!
Soft shadows? There is only one point light in the scene, no area
lights. I did use MegaPOV radiosity, that is probably what causes the
realistic lighting...it looks quite bad without radiosity.
Or did you mean the way the shadows from the spines break up the outline?
--
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/
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reminds me of a 3d image i saw years ago, a cactus like that, in a pot with
arms and feet, in front of some blinds..
very nice :)
Rick
"Chris Huff" <chr### [at] yahoocom> wrote in message
news:chrishuff_99-9D37D5.05283324022000@news.povray.org...
> Here is my first attempt at a cactus in MegaPOV(inspired by some
> discussions in the thread "A clock"), it uses trace() and an isosurface.
> The texturing still needs a lot of work...
>
> --
> Chris Huff
> e-mail: chr### [at] yahoocom
> Web page: http://chrishuff.dhs.org/
>
>
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<juh### [at] kolumbusfi> wrote:
> That looks great. If I can't come up with a good cactus could you share
> the code ? :)
See povray.text.scene-files:
Chris Huff IsoCactus 2/24/2000 4:14 PM
> Maybe just a slight granite normal scaled bigger in y than in x and z
> ? I'll go fech some books since I haven't taken a better look at the
> "texture" of real cactii :)
Granite, or dents, or maybe agate...something to give some smaller scale
features to the surface. And some color variation.
And a halfway decent sand texture. Maybe some rocks and other plants.
--
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/
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Great! I have one of this type but it has fewer pleats and a smaller "dent"
in the top.
Could be a tad darker in color I think.
--
___ ______________________________________________________
| \ |_ <dav### [at] faricynet> <ICQ 55354965>
|_/avid |ontaine http://www.faricy.net/~davidf/
"Sitting on a cornflake, waiting for the van to come" -Beatles
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I like it! Tricky trace work there. I just recently found out that using
just method 2 and eval with a very low accuracy (about .001) gives the best
results. I hope to work on my tutorial soon :)
Chris Huff wrote:
> Here is my first attempt at a cactus in MegaPOV(inspired by some
> discussions in the thread "A clock"), it uses trace() and an isosurface.
> The texturing still needs a lot of work...
>
> --
> Chris Huff
> e-mail: chr### [at] yahoocom
> Web page: http://chrishuff.dhs.org/
>
> [Image]
--
Samuel Benge
E-Mail: STB### [at] aolcom
Visit the still unfinished isosurface tutorial:
http://members.aol.com/stbenge
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In article <38B5EA14.BC81C7D6@aol.com>, "SamuelT." <STB### [at] aolcom>
wrote:
> I like it! Tricky trace work there. I just recently found out that
> using just method 2 and eval with a very low accuracy (about .001)
> gives the best results. I hope to work on my tutorial soon :)
Hmm, actually, that is a pretty high accuracy. :-)
Maybe this keyword should be changed to something like "allowable_error"
in the official version...
I confess that I haven't tweaked the settings for this isosurface at
all...it rendered as wanted and wasn't too slow, so I just didn't
bother. I just typed in the equation, liked the results, gave it a plain
green pigment, and began playing with trace().
--
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/
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Bravo!!!
Eric
--------------------
http://www.datasync.com/~ericfree
--------------------
"The whole problem with the world is that fools and fanatics are always so
certain of themselves, but wiser people so full of doubts."
--Bertrand Russel
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"Chris Huff" <chr### [at] yahoocom> wrote in message
news:chrishuff_99-00EEB8.15435524022000@news.povray.org...
>
> function {
> sqrt(
> sqr(x)
> + sqr(y-sqrt(sqr(x/2)+sqr(z/2))*1.5)
> + sqr(z)
> ) - 1
> - (sin(TH(x, y, z)*18)*0.1)//This is what makes the ridges
> }
How did you come up with this? Luck? Patience? Or did you say, "hmm...
the formula for a cactus should be blah blah blah" and just whip it up?
Even tho I've had a couple semesters of calculus and physics (20 years ago)
I have no clue how to take an idea and make an iso-surface out of it.
Eric
--------------------
http://www.datasync.com/~ericfree
--------------------
"The whole problem with the world is that fools and fanatics are always so
certain of themselves, but wiser people so full of doubts."
--Bertrand Russel
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In article <38b7154e@news.povray.org>, "Eric Freeman"
<eri### [at] datasynccom> wrote:
> How did you come up with this? Luck? Patience? Or did you say, "hmm...
> the formula for a cactus should be blah blah blah" and just whip it up?
> Even tho I've had a couple semesters of calculus and physics (20 years
> ago)
> I have no clue how to take an idea and make an iso-surface out of it.
No calculus or physics required. If there were, I wouldn't be able to
accomplish anything. I am still in Algebra II.
Well, the cactus is approximately spherical, with an indentation in the
middle and radial ridges.
I started from the equation for a sphere:
function {
sqrt(
sqr(x)
+ sqr(y)
+ sqr(z)
) - 1
}
To indent the top of the cactus and extend the bottom, I modified the y
portion of the equation like this:
+ sqr(y-sqrt(sqr(x/2)+sqr(z/2))*1.5)
This subracts a certain amount from the y value which depends on the
distance from the y axis. The /2 and *1.5 were just to "tune" it to the
right proportions. Subtracting from the y value has the effect of
raising that portion of the surface, since a higher initial value is
required to reach the threshold value. This modification really raises
the sides of the cactus, although a variant of it could be made to
depress the middle.
Then to add the "ridges", I subtracted a value depending on the sine of
a multiple of the angle around the y axis from the total density:
- (sin(atan2(x, z)*18)*0.1)
(note that while this is slightly different from the other version, it
is really just a different way of calling the same function.)
The angle around the y axis can be calculated by atan2(x,z), which
returns the angle in radians. This is ok, since the sin() function takes
radians. I then multiply by 18 to get 18 "cycles" for a full revolution.
Since the sin() function returns values between -1 and 1, I multiplied
it's result by 0.1 to get shallower ridges. This makes the ridges extend
from about 0.1 units "below" the surface of the original sphere-like
shape to about 0.1 units "above" it. Because the function returns both
positive and negative values equally, I could just have easily used
addition to incorporate it into the equation.
I probably did a very poor job of explaining it, but that is how I came
up with this equation. I tend to have more success visualizing the
isosurface as a density function with a "skin" at a certain density
level(the threshold value). I start with a basic shape and progressively
"sculpt" the density pattern by tweaking the function, adding
characteristics to the function, and adding other density functions into
the mix.
--
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/
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