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"Mahalis" <don### [at] fakey com> wrote in message
news:3ba90af9$1@news.povray.org...
> How can you tell what the radius of a blob will be at any particular point
> (is there some sort of formula)? Whenever I try to position a regular
sphere
> touching a blob, it doesn't look anything like I want it to.
I am sure there is a formula for more complex shapes, but the general
idea is simple. If your radius is 1 and the threshold is 0.5, the surface is
0.5 units from the origin.
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"Bill DeWitt" wrote:
> I am sure there is a formula for more complex shapes,
> but the general idea is simple. If your radius is 1 and
> the threshold is 0.5, the surface is 0.5 units from the
> origin.
That's not true. In this case it's pretty close to 0.5, but if you try to
change the threshold to 0.1 or 0.9 you'll see great differences. BTW, this
all assumes that the strength is 1; I'm sure that's what you meant too.
I can't remember the real formula right now, but it should be possible to
derive it from my easyblob macro, which you can find here:
http://rsj.mobilixnet.dk/3d/blobs/blobs.html
Rune
--
3D images and anims, include files, tutorials and more:
Rune's World: http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users: http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk
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Rune wrote:
>>I can't remember the real formula right now, but it should be possible to
The formula is radius*(threshold -1)*strength. In other words, if your
threshold is .4, your radius is 1, and your strength is 1, the apparent size
of your blob component will be (1-.4)*1*1 or .6*1*1, or .6.
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Dave Dunn wrote:
> Rune wrote:
> >>I can't remember the real formula right now, but it should be possible to
>
> The formula is radius*(threshold -1)*strength. In other words, if your
> threshold is .4, your radius is 1, and your strength is 1, the apparent size
> of your blob component will be (1-.4)*1*1 or .6*1*1, or .6.
That should be, of course (1-threshold) :{
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Dave Dunn wrote:
>
> Rune wrote:
> >>I can't remember the real formula right now, but it should be possible to
>
> The formula is radius*(threshold -1)*strength. In other words, if your
> threshold is .4, your radius is 1, and your strength is 1, the apparent size
> of your blob component will be (1-.4)*1*1 or .6*1*1, or .6.
The R*S*(1-T) formula falls down for strength != 1. It can give an
observed radius larger than the given radius which never happens.
Actually, the density of a single spherical blob is given in ss6.5.1.1
of the v3.5 docs. Since the observed radius is where the density equals
the threshold, actual radius is given as
A = R*sqrt(1-sqrt(T/S))
where
R = given radius
S = component strength
T = threshold
so your example of T = 0.4, S = 1, R = 1 gives A = ~0.606
Bet you wanted to know that, hmm? :-)
Bye for now,
Mike Andrews.
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Michael Andrews wrote:
>>The R*S*(1-T) formula falls down for strength != 1.
Who knew, heh heh. Guess I never use strengths other than 1 or -1. Live and learn.
Thanks for the tip.
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Thought I'd try and salvage a bit of my integrity, anyway. The formula I gave for the
visible size of a blob component will work when the strength value <1. In other words,
if your strength is .5, you can apply the formula to get the apparent radius. Where it
breaks down is if strength >1.
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Jettison all math. If you have a cool blob object, it will have dozens of
components, no?
Use the trace function.
Mahalis wrote:
> How can you tell what the radius of a blob will be at any particular point
> (is there some sort of formula)? Whenever I try to position a regular sphere
> touching a blob, it doesn't look anything like I want it to.
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On Wed, 19 Sep 2001 17:17:20 -0400, "Mahalis" <don### [at] fakeycom>
wrote:
>How can you tell what the radius of a blob will be at any particular point
>(is there some sort of formula)? Whenever I try to position a regular sphere
>touching a blob, it doesn't look anything like I want it to.
Use trace() :)
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG e-mail : pet### [at] tagpovrayorg
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Dave Dunn wrote:
>
> Thought I'd try and salvage a bit of my integrity, anyway. The formula I gave for
the
> visible size of a blob component will work when the strength value <1. In other
words,
> if your strength is .5, you can apply the formula to get the apparent radius. Where
it
> breaks down is if strength >1.
Heh! In mine, if the strength is less than the threshold you get to take
the square root of a negative number ... this equates to having an
imaginary surface, I guess. Just too complex for a Friday evening.
Hmm, sorry about the bad punning, it's been a long day.
Here's hoping for a quiet weekend ...
Bye for now,
Mike Andrews.
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