I am trying to create circular walls with radius and diameter values or from
which I can obtain said values. I am trying to stay away from CSG so I am
thinking of cubic_splines in prisms. I have been studying the code from Block
Wall Macros specifically the macro Blockwall_Arc(360,"") but it has been
difficult for me. Is there anybody that can make this code clearer for me...
tried to find a way to contact Chris Bartlett (I think, who wrote the code but
he seems very scarce on the net). Any help will be greatly appreciated. I am
guessing this is OK to include the code here. Perhaps studying it here will make
it easier for somebody to explain it to me.

Basically, I want to be able to plug in radius and/or diameter values to get a
circular wall or I would like to use this method but then be able to extract
radius and/or diameter values from it. Cheers!

//  This macro creates a circular (cylindrical) wall or a segment of a circular
wall.
//
#macro Blockwall_Arc (Blockwall_ArcDegrees, Blockwall_BlockType)
  #ifndef(Blockwall_Radius) #declare Blockwall_Radius  = 1;    #end
  #declare Blockwall_Spline = spline {
    cubic_spline
    #local Blockwall_I = -0.25;
    #while (Blockwall_I<=1.25)
      Blockwall_I, vrotate(Blockwall_Radius*z,
y*Blockwall_I*Blockwall_ArcDegrees)
      #local Blockwall_I = Blockwall_I + 0.01;
    #end
  }
  object {Blockwall_FollowSpline(Blockwall_BlockType)}
#end

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> I am trying to create circular walls with radius and diameter values or from
> which I can obtain said values. I am trying to stay away from CSG so I am
> thinking of cubic_splines in prisms. I have been studying the code from Block
> Wall Macros specifically the macro Blockwall_Arc(360,"") but it has been
> difficult for me. Is there anybody that can make this code clearer for me...
> tried to find a way to contact Chris Bartlett (I think, who wrote the code but
> he seems very scarce on the net). Any help will be greatly appreciated. I am
> guessing this is OK to include the code here. Perhaps studying it here will make
> it easier for somebody to explain it to me.
>
> Basically, I want to be able to plug in radius and/or diameter values to get a
> circular wall or I would like to use this method but then be able to extract
> radius and/or diameter values from it. Cheers!
>
> //  This macro creates a circular (cylindrical) wall or a segment of a circular
> wall.
> //
> #macro Blockwall_Arc (Blockwall_ArcDegrees, Blockwall_BlockType)
>    #ifndef(Blockwall_Radius) #declare Blockwall_Radius  = 1;    #end
>    #declare Blockwall_Spline = spline {
>      cubic_spline
>      #local Blockwall_I = -0.25;
>      #while (Blockwall_I<=1.25)
>        Blockwall_I, vrotate(Blockwall_Radius*z,
> y*Blockwall_I*Blockwall_ArcDegrees)
>        #local Blockwall_I = Blockwall_I + 0.01;
>      #end
>    }
>    object {Blockwall_FollowSpline(Blockwall_BlockType)}
> #end
>
>
>

That macro is not self contained.
First : It create a spline that follows a circular path. For that, it 
use an externaly created variable: Blockwall_Radius.
It also use 2 passed parameters: A value in degrees and a reference 
value defining what kind of blocks to use.

Then, once the spline is constructed, it use another macro 
(Blockwall_FollowSpline) to place blocks along that spline, surely 
binded in an union so that you can place the result anywhere you need it.

What this macro _DON'T DO_: Create a prism.
It /DOES/ use CSG as an union of numerous blocks.



Alain

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Alain <aze### [at] qwertyorg> wrote:

>
> That macro is not self contained.
> First : It create a spline that follows a circular path. For that, it
> use an externaly created variable: Blockwall_Radius.
> It also use 2 passed parameters: A value in degrees and a reference
> value defining what kind of blocks to use.
>
> Then, once the spline is constructed, it use another macro
> (Blockwall_FollowSpline) to place blocks along that spline, surely
> binded in an union so that you can place the result anywhere you need it.
>
> What this macro _DON'T DO_: Create a prism.
> It /DOES/ use CSG as an union of numerous blocks.
>
>
>
> Alain

I suspected that. OK, is there a way to create a spline path that can be used to
draw a prism of a particular radius or diameter. I can do trial and error and
end up with an approximation but I was wondering if there is a way to get a
mathematically precise method that can generate values for any radius or
diameter.

Post a reply to this message

Am 17.09.2010 23:16, schrieb Kene:

> I suspected that. OK, is there a way to create a spline path that can be used to
> draw a prism of a particular radius or diameter. I can do trial and error and
> end up with an approximation but I was wondering if there is a way to get a
> mathematically precise method that can generate values for any radius or
> diameter.

There's no mathematically /exact/ way whatsoever to represent a circular 
arc with a finite sequence of cubic splines (and all splines in POV-Ray 
are effectively cubic splines or special cases thereof). Neither for the 
general case, nor for any specific case (except maybe pathological ones).

Post a reply to this message

> Alain<aze### [at] qwertyorg>  wrote:
>
>>
>> That macro is not self contained.
>> First : It create a spline that follows a circular path. For that, it
>> use an externaly created variable: Blockwall_Radius.
>> It also use 2 passed parameters: A value in degrees and a reference
>> value defining what kind of blocks to use.
>>
>> Then, once the spline is constructed, it use another macro
>> (Blockwall_FollowSpline) to place blocks along that spline, surely
>> binded in an union so that you can place the result anywhere you need it.
>>
>> What this macro _DON'T DO_: Create a prism.
>> It /DOES/ use CSG as an union of numerous blocks.
>>
>>
>>
>> Alain
>
> I suspected that. OK, is there a way to create a spline path that can be used to
> draw a prism of a particular radius or diameter. I can do trial and error and
> end up with an approximation but I was wondering if there is a way to get a
> mathematically precise method that can generate values for any radius or
> diameter.
>
>

Quick and dirty:
- Remove the call to the other macro.
- Start your prism.
- Call the macro twice: once with the inside radius of your wall and 
travel it to create the iner part of the prism. (use a loop)
- SAVE the first point!
- Call the macro a second time with the outside radius and travel the 
spline backward to create the outside of the prism.
- Close the prism by adding the last point equal to the first one.
- Add any needed transformation and texturing.
- Finish the prism.

That's for a prism using a linear_spline interpolation.
If you want to use a cubic_spline interpolation, then the last TWO 
points must repeat the first two points. The first and last points are 
controls, the second and secont to last are real points.


Alain

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Alain <aze### [at] qwertyorg> wrote:

> > Alain<aze### [at] qwertyorg>  wrote:

>
> Quick and dirty:
> - Remove the call to the other macro.
> - Start your prism.
> - Call the macro twice: once with the inside radius of your wall and
> travel it to create the iner part of the prism. (use a loop)
> - SAVE the first point!
> - Call the macro a second time with the outside radius and travel the
> spline backward to create the outside of the prism.
> - Close the prism by adding the last point equal to the first one.
> - Add any needed transformation and texturing.
> - Finish the prism.
>
> That's for a prism using a linear_spline interpolation.
> If you want to use a cubic_spline interpolation, then the last TWO
> points must repeat the first two points. The first and last points are
> controls, the second and secont to last are real points.
>
>
> Alain

Interesting! This is what I am looking for. Let me see if I can get it to work.
Thanks...

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