The texture

    texture {
       pigment {
          gradient x
          color_map {
             [0  Gray35]
             [1  Gray40]
             }
    //    scale 0.30
          frequency 1/0.30
          }
       }  // end of base texture

is supposed to produce a repeating gradient every 30 centiunits.  However,
there are also lines visible at the position of the original un-modified
gradient.  It's as if both the 0->1 gradient and the 0->0.3 gradient are
layered.

If I use a scale instead of frequency, I get the desired effect.
The docs say that the effects should be identical.

What's up?

--John

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On Thu, 16 Sep 1999 22:13:29 -0500, "John M. Dlugosz"
<joh### [at] dlugoszcom> wrote:

>If I use a scale instead of frequency, I get the desired effect.
>The docs say that the effects should be identical.
>
>What's up?

You're misreading the docs.  

| The frequency keyword adjusts the number of times that a color map 
| repeats over one cycle of a pattern. For example gradient covers color    
| map values 0 to 1 over the range from x=0 to x=1. By adding frequency
| 2.0 the color map repeats twice over that same range. 

The pattern doesn't change.  Just the color map does.  So saying
  color_map {[0 rgb 0][1 rgb 1]} frequency 2.0
is like saying
  color_map {[0 rgb 0][1/2 rgb 1][1/2 rgb 0][1 rgb 1]}
but saying
  color_map {[0 rgb 0][1 rgb 1]} frequency 1.5
is like saying
  color_map {[0 rgb 0][2/3 rgb 1][2/3 rgb 0][4/3 rgb 1]}
except that that isn't legal.  So POV truncates the color
map at 1.

You're probably referring to this sentence:

| The same effect can be achieved using scale 0.5*x so the frequency keyword 
| isn't that useful for patterns like gradient.

The problem is, that sentence isn't definitive.  It just points out
that the results of THAT SPECIFIC OPERATION are identical to a scale.
Noninteger frequencies are not identical to a scale.

Post a reply to this message

Ron Parker <par### [at] fwicom> wrote:
: | The same effect can be achieved using scale 0.5*x so the frequency keyword 
: | isn't that useful for patterns like gradient.

  Is this true even if you use 'turbulence'?

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Nieminen Juha wrote:
> 
> Ron Parker <par### [at] fwicom> wrote:
> : | The same effect can be achieved using scale 0.5*x so the frequency keyword
> : | isn't that useful for patterns like gradient.
> 
>   Is this true even if you use 'turbulence'?

I don't see where turbulence would have any effect on the order of the
color map in a pattern. Turbulence will 'bend' the pattern but will not
change it.

-- 
Ken Tyler

See my 1000+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

Post a reply to this message

Ken <tyl### [at] pacbellnet> wrote:
:> : | The same effect can be achieved using scale 0.5*x so the frequency keyword
:> : | isn't that useful for patterns like gradient.
:> 
:>   Is this true even if you use 'turbulence'?

: I don't see where turbulence would have any effect on the order of the
: color map in a pattern. Turbulence will 'bend' the pattern but will not
: change it.

  Scaling a "turbulenced" pattern by 0.5*x is certainly not the same as
just setting its frequency to 2. When you scale the pattern, the shape of
the "bending" changes but when you only change the frequency that doesn't
change the shape of the pattern.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Without testing, I'd say
{gradient x scale .5*x warp{turbulence .5}} =
{gradient x frequency 2 turbulence .5}

Turblence is entirely separate from the pattern; it's a variation of 3d
Perlin noise whose value at point P affects the pattern value at that
point. The difference arises from wether turbulence is or is not
transformed with the pattern. Frequency affects _only_ the pattern.

Margus

Nieminen Juha wrote:
> 
>   Scaling a "turbulenced" pattern by 0.5*x is certainly not the same as
> just setting its frequency to 2. When you scale the pattern, the shape of
> the "bending" changes but when you only change the frequency that doesn't
> change the shape of the pattern.
> 
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

On 17 Sep 1999 03:22:19 -0400, Nieminen Juha wrote:
>Ron Parker <par### [at] fwicom> wrote:
>: | The same effect can be achieved using scale 0.5*x so the frequency keyword 
>: | isn't that useful for patterns like gradient.
>
>  Is this true even if you use 'turbulence'?

No, because of the order of evaluation.  But my point was that it's not
even true in all simple cases, just in the specific case mentioned in 
the docs and in other cases of integer frequency.

Post a reply to this message

Ron Parker <par### [at] fwicom> wrote in message
news:37e3b6a6.257855790@news.povray.org...
> The pattern doesn't change.  Just the color map does.  So saying
>  ...
> The problem is, that sentence isn't definitive.  It just points out
> that the results of THAT SPECIFIC OPERATION are identical to a scale.
> Noninteger frequencies are not identical to a scale.

Gotcha.

So the advice on using "frequency" with a texture map, seen a week or two
ago, isn't right either.

--John

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