In my previous post I talked about adding random translation/rotation into
my tunnel building script. I've played around with the rand() function with
mixed results. From what I understand it works like so

#declare myseed = seed(12);

translate <0,0,rand(myseed)>

The problem with this is that the random value you get is only between 0 and
1. SO I tried the following.

translate <0,0,rand(myseed)/rand(myseed)> or
translate <0,0,rand(myseed)/rand(myseed)*rand(myseed)>

This does work better but I still don't get the effect I want. With this
method most of the objects are still only translated an imperceptible
amount, and then every once in a while an object will be translated a large
distance. What I want is for all the objects to be noticeably translated a
random amount, but I don't want any sudden leaps.

Post a reply to this message

Random numbers are lots of fun. Generally, you need to multiply the random
number by some amount and then add or subtract a constant in order to get
random numbers within the range that you want. For example, if you want real
random numbers between 20 and 25, you could do this:
    #local NewZ = rand (MySeed) * 5 + 20;

If you want integer random numbers between -3 and 3, you could do this:
    #local NewZ = int (rand (MySeed) * 7) - 3;

Here's one more example: To get numbers between .2 and .3, you could use
this:
    #local NewZ = rand (MySeed) * .1 + .2;

Have fun,
Dave Blandston
--------------------------------------

"Thomas Lake" <tla### [at] homecom> wrote in message
news:3afdcb2e$1@news.povray.org...
> In my previous post I talked about adding random translation/rotation into
> my tunnel building script. I've played around with the rand() function
with
> mixed results. From what I understand it works like so
>
> #declare myseed = seed(12);
>
> translate <0,0,rand(myseed)>
>
> The problem with this is that the random value you get is only between 0
and
> 1. SO I tried the following.
>
> translate <0,0,rand(myseed)/rand(myseed)> or
> translate <0,0,rand(myseed)/rand(myseed)*rand(myseed)>
>
> This does work better but I still don't get the effect I want. With this
> method most of the objects are still only translated an imperceptible
> amount, and then every once in a while an object will be translated a
large
> distance. What I want is for all the objects to be noticeably translated a
> random amount, but I don't want any sudden leaps.
>
>

Post a reply to this message

Thanks for the info! I'm trying to find out how to create random numbers
between -0.75 and 0.75. I tried to come up with the function using your
examples but I can't seem to get it right. The general for seems to be

Num = rand*x + y

so

-0.75 = 0.1*x +y and
0.75 = 0.9*x +y

I've tried solving for x and y, buy graphing and calculating the
intersection of the 2 lines, but this doesn't work.


"Dave Blandston" <gra### [at] earthlinknet> wrote in message
news:3afdcfd6@news.povray.org...
> Random numbers are lots of fun. Generally, you need to multiply the random
> number by some amount and then add or subtract a constant in order to get
> random numbers within the range that you want. For example, if you want
real
> random numbers between 20 and 25, you could do this:
>     #local NewZ = rand (MySeed) * 5 + 20;
>
> If you want integer random numbers between -3 and 3, you could do this:
>     #local NewZ = int (rand (MySeed) * 7) - 3;
>
> Here's one more example: To get numbers between .2 and .3, you could use
> this:
>     #local NewZ = rand (MySeed) * .1 + .2;
>
> Have fun,
> Dave Blandston
> --------------------------------------
>
> "Thomas Lake" <tla### [at] homecom> wrote in message
> news:3afdcb2e$1@news.povray.org...
> > In my previous post I talked about adding random translation/rotation
into
> > my tunnel building script. I've played around with the rand() function
> with
> > mixed results. From what I understand it works like so
> >
> > #declare myseed = seed(12);
> >
> > translate <0,0,rand(myseed)>
> >
> > The problem with this is that the random value you get is only between 0
> and
> > 1. SO I tried the following.
> >
> > translate <0,0,rand(myseed)/rand(myseed)> or
> > translate <0,0,rand(myseed)/rand(myseed)*rand(myseed)>
> >
> > This does work better but I still don't get the effect I want. With this
> > method most of the objects are still only translated an imperceptible
> > amount, and then every once in a while an object will be translated a
> large
> > distance. What I want is for all the objects to be noticeably translated
a
> > random amount, but I don't want any sudden leaps.
> >
> >
>
>

Post a reply to this message

Thomas Lake wrote:
> 
> Thanks for the info! I'm trying to find out how to create random numbers
> between -0.75 and 0.75. I tried to come up with the function using your
> examples but I can't seem to get it right. The general for seems to be
> 
> Num = rand*x + y
> 

where x is the range of values and y the center minus half the range (or
the lowest value):

#declare Num = rand(Seed)*1.5 - 0.75;

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message

In article <3afe4401$1@news.povray.org>, tla### [at] homecom says...
> Thanks for the info! I'm trying to find out how to create random numbers
> between -0.75 and 0.75. I tried to come up with the function using your
> examples but I can't seem to get it right. The general for seems to be

This macro returns a random number between R_min and R_max
in your case use random(MySeed,-0.75,0.75)

#macro random(Myseed,R_min,R_max)
	(rand(MySeed)*(R_max-R_min) + R_min)
#end


> Num = rand*x + y
> so

> -0.75 = 0.1*x +y and
> 0.75 = 0.9*x +y
Wrong. 
-0.75 = 0*x+y
0.75 = 1*x+y

so
y = -0.75  // = R_min
x = 2*0.75 = 0.75 - (-0.75) // = R_max - R_min

Lutz-Peter

Post a reply to this message

I forget where I found this, but I've had it awhile.

#macro rand_ext(M,D,Seed)
  (M+(rand(Seed)-.5)*2*D)
#end

This macro returns a random number in a range where M is the mean value, D
is the negative and positive deviation from this mean, and Seed is a
seed([number]) value.

For instance, the line #declare fromfivetofifteen=rand_ext(10,5,seed(123));
would return a random value between 5 and 15.

-Chris-

Thomas Lake <tla### [at] homecom> wrote in message
news:3afdcb2e$1@news.povray.org...
> In my previous post I talked about adding random translation/rotation into
> my tunnel building script. I've played around with the rand() function
with
> mixed results. From what I understand it works like so
>
> #declare myseed = seed(12);
>
> translate <0,0,rand(myseed)>
>
> The problem with this is that the random value you get is only between 0
and
> 1. SO I tried the following.
>
> translate <0,0,rand(myseed)/rand(myseed)> or
> translate <0,0,rand(myseed)/rand(myseed)*rand(myseed)>
>
> This does work better but I still don't get the effect I want. With this
> method most of the objects are still only translated an imperceptible
> amount, and then every once in a while an object will be translated a
large
> distance. What I want is for all the objects to be noticeably translated a
> random amount, but I don't want any sudden leaps.
>
>

Post a reply to this message