POV-Ray : Newsgroups : povray.advanced-users : Random tree position, without duplicates? Server Time: 28 Sep 2020 22:10:50 GMT
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From: Jim Charter
Subject: Re: Random tree position, without duplicates?
Date: 5 Jun 2010 22:49:22
Message: <4c0ad472$1@news.povray.org>
Edouard wrote:
> Jim Charter <jrc### [at] msncom> wrote:
>> Edouard wrote:
>>> SharkD <mik### [at] gmailcom> wrote:
>>>> On 6/4/2010 5:31 PM, Edouard wrote:
>>>>> "Edouard"<pov### [at] edouardinfo>  wrote:
>>>>>
>>>>> Opps - I mean:
>>>>>
>>>>> #macro halton2D( n )
>>>>>   #local baseX = 2;
>>>>>   #local baseY = 3;
>>>>>
>>>>>   <  halton( n, baseX ), halton( n, baseY ), 0>
>>>>> #end
>>>> Could you provide an example of how to use it? Thanks.
>>> I'll try!
>>>
>>> The halton macro returns a number from 0..1, and halton2D() returns a vector
>>> where the X is 0..1, Y is 0..1 and the Z = 0.
>>>
>>> You call halton2D() with an incrementing integer, so it works best in a loop.
>>>
>>> If you had a macro called PlaceTree(), you could loop through values from
>>> halton2D calling the tree macro like this:
>>>
>>> #declare n = 1;
>>> #while( n < number_of_trees_wanted )
>>>   #declare position = halton2D( n );
>>>   // position is <0..1, 0..1, 0> - scale the vector here
>>>   // to the size you need for PlaceTree
>>>   PlaceTree( position )
>>>   #declare n = n + 1;
>>> #end
>>>
>>> Does my explanation make sense?
>>>
>>> Cheers,
>>> Edouard.
>>>
>>>
>> This is very useful! I see that the increasing integer eliminates the
>> overlap of points.  Is there a relationship between the size of the
>> object and the size of the increment that can be used to prevent
>> objects intersecting?
> 
> Unfortunately not - all it does is generate numbers that have a distribution
> that looks random, but have the property that they don't clump together. As you
> generate more numbers, each new item fills a position that was empty, and as you
> generate more and more numbers in the sequence, space gets filled denser and
> denser.
> 
> If your objects aren't too closely packed, a halton sequence is a very easy
> replacement for rand(), and may work well. I posted it mainly because it should
> be very easy to try out for the problem described.
> 
> Cheers,
> Edouard.
> 
> 
It's a revelation, thanks.


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