POV-Ray : Newsgroups : povray.general : How to check if two objects have any intersection? Server Time: 30 Mar 2020 14:27:35 GMT
  How to check if two objects have any intersection? (Message 1 to 4 of 4)  
From: Kima
Subject: How to check if two objects have any intersection?
Date: 30 Jan 2020 21:10:00
Message: <web.5e33452eb572e6a0ecc0fada0@news.povray.org>
I need an if statement to check if two objects have any intersection. I assumed
trace(a, b) should give false when there is no intersection, something like

 #if ( trace(a,b) )
   ....
 #else
   ....
 #end

but apparently, trace return a vector, when if statement needs a numeric
expression.

How can I check if two objects have any overlap in an if statement?


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From: jr
Subject: Re: How to check if two objects have any intersection?
Date: 30 Jan 2020 21:55:00
Message: <web.5e33502f78dd1088451952ca0@news.povray.org>
hi,

"Kima" <nomail@nomail> wrote:
> I need an if statement to check if two objects have any intersection. I assumed
> trace(a, b) should give false when there is no intersection, something like
>
>  #if ( trace(a,b) )
>    ....
>  #else
>    ....
>  #end
>
> but apparently, trace return a vector, when if statement needs a numeric
> expression.
>
> How can I check if two objects have any overlap in an if statement?

I guess you'd need to write a macro which takes the two objects and returns a
bool, true if the bounding boxes overlap (or whichever method you use to
determine "intersection").


regards, jr.


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From: Bald Eagle
Subject: Re: How to check if two objects have any intersection?
Date: 30 Jan 2020 22:40:00
Message: <web.5e335a3d78dd10884eec112d0@news.povray.org>
"Kima" <nomail@nomail> wrote:

> but apparently, trace return a vector, when if statement needs a numeric
> expression.

Well, since trace {} returns <0, 0, 0> as the surface normal if it misses the
object, then you can just add together the x, y, and z components of the vector
to give a scalar value.  Use abs() so nothing cancels out.

#declare TraceBool = abs(Normal.x)+abs(Normal.y)+abs(Normal.z);

http://news.povray.org/povray.binaries.tutorials/thread/%3Cweb.51f61e827603294573fc9ebb0%40news.povray.org%3E/

Gonna be tricky with CSG to look at the right place and get an accurate result.
If they are curves / algebraic surfaces, then I might see about doing the math
to see if there are any intersection points.

Just curious - what if you did:
intersection {
     ObjectA
     ObjectB
}
and computed the volume of the bounding box?

At the very least, if you're "scanning" with trace{}, then it would give you a
much smaller, and accurate volume to focus on.


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From: Alain Martel
Subject: Re: How to check if two objects have any intersection?
Date: 31 Jan 2020 17:01:23
Message: <5e345d63$1@news.povray.org>
Le 2020-01-30 à 17:35, Bald Eagle a écrit :
> 
> "Kima" <nomail@nomail> wrote:
> 
>> but apparently, trace return a vector, when if statement needs a numeric
>> expression.
> 
> Well, since trace {} returns <0, 0, 0> as the surface normal if it misses the
> object, then you can just add together the x, y, and z components of the vector
> to give a scalar value.  Use abs() so nothing cancels out.
> 
> #declare TraceBool = abs(Normal.x)+abs(Normal.y)+abs(Normal.z);
> 
>
http://news.povray.org/povray.binaries.tutorials/thread/%3Cweb.51f61e827603294573fc9ebb0%40news.povray.org%3E/
> 
> Gonna be tricky with CSG to look at the right place and get an accurate result.
> If they are curves / algebraic surfaces, then I might see about doing the math
> to see if there are any intersection points.
> 
> Just curious - what if you did:
> intersection {
>       ObjectA
>       ObjectB
> }
> and computed the volume of the bounding box?
> 
> At the very least, if you're "scanning" with trace{}, then it would give you a
> much smaller, and accurate volume to focus on.
> 
> 

You can test for the length of the normal vector.
If the trace encounter a surface, the length is 1. If it miss, the 
length is zero.

So, it become :
#declare TraceBool = vlength(Normal);


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