Hello, all.

I've been messing about with Ron Parker's pattern image type to make me some
quick heightfields in MegaPOV 0.6a, and something caught my eye.

The heightfield in the attached image was made up from the following code:

height_field {
  pattern 1000,1000 {
    hf_gray_16
    dents
    colour_map {
      [0.0 rgb 0.0]
      [0.4 rgb 0.0]
      [0.5 rgb 0.1]
      [0.6 rgb 0.8]
      [0.7 rgb 1.0]
      [1.0 rgb 1.0]
    }
    scale 0.25
  }
  pigment {gradient y colour_map {[0 rgb <1,0,0>] [1 rgb <0,0,1>]}}
  translate <-0.5,0,-0.5>
  scale <200,20,200>
}

Looking at the resulting image, it appears that the graduations between the
different greyscales in the colour_map are linear, rather than nice and
smooth in a spliney sort of way.

This right?  Only asking because it seems to go against what's said in the
help file: 'Most of the color patterns do not use abrupt color changes of
just two or three colors like those in the brick, checker or hexagon
patterns. They instead use smooth transitions of many colors that gradually
change from one point to the next.'

Bye,
Alan.

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Attachments:
Download 'colour_map.jpg' (4 KB)

Preview of image 'colour_map.jpg'

If you want things to be spliney, look in the docs for "wave types", and
you'll find cubic_wave, sine_wave and such.

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Alan Holding wrote:
> 
> [...]
> 
> This right?  Only asking because it seems to go against what's said in the
> help file: 'Most of the color patterns do not use abrupt color changes of
> just two or three colors like those in the brick, checker or hexagon
> patterns. They instead use smooth transitions of many colors that gradually
> change from one point to the next.'
> 

Well, it's not really an abrupt change in the value, but in the slope. 
Anyway it looks somewhat strange.  It's probably specific for the 'dents'
pattern, but i don't know, because i'm not using it very often.  

Christoph

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

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Tony[B] <ben### [at] catholicorg> wrote in message
news:3a539907@news.povray.org...
> If you want things to be spliney, look in the docs for
> "wave types", and you'll find cubic_wave, sine_wave
> and such.

Weeell...

Had a go, but the only one which came close was a scaled up poly_wave (see
attached).  I don't think there's a way round this because, as stated in the
help file, 'Although any of these wave types can be used for pigments,
normals, textures, or density the effect of many of the wave types are not
as noticeable on pigments, textures, or density as they are for normals.'

Ah, phooey!

Bye,
Alan.

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Attachments:
Download 'sine_wave.jpg' (4 KB) Download 'poly_wave2.jpg' (5 KB) Download 'scallop_wave.jpg' (9 KB) Download 'cubic_wave.jpg' (6 KB)

Preview of image 'sine_wave.jpg'

Preview of image 'poly_wave2.jpg'

Preview of image 'scallop_wave.jpg'

Preview of image 'cubic_wave.jpg'

In article <3a539907@news.povray.org>, "Tony[B]" <ben### [at] catholicorg> 
wrote:

> If you want things to be spliney, look in the docs for "wave types", and
> you'll find cubic_wave, sine_wave and such.

Those only affect the waveform of the pattern. They won't smooth out the 
color_map, they will just move things around a bit and sometimes make 
the transitions non-flat.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Alan Holding wrote:
> 
> Had a go, but the only one which came close was a scaled up poly_wave (see
> attached).  I don't think there's a way round this because, as stated in the
> help file, 'Although any of these wave types can be used for pigments,
> normals, textures, or density the effect of many of the wave types are not
> as noticeable on pigments, textures, or density as they are for normals.'
> 

This applies for pigments, but not for use with heightfields and
isosurfaces.  Tony's idea was quite good for smoothing the pattern itself,
but in your case it does not help much because of the color_map.  

The following should look better, because the color_map is much
'smoother':

    dents
    colour_map {  
      [0.0 rgb 0.0]
      [0.3 rgb 0.1]
      [0.4 rgb 0.2]
      [0.6 rgb 0.7]
      [0.8 rgb 0.9]
      [1.0 rgb 1.0]      
    }

You can also try to specify a more detailed color_map using a #while loop
for example.  

Christoph

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

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In article <3a539535@news.povray.org>, "Alan Holding" 
<man### [at] lineonenet> wrote:

> This right?  Only asking because it seems to go against what's said 
> in the help file: 'Most of the color patterns do not use abrupt color 
> changes of just two or three colors like those in the brick, checker 
> or hexagon patterns. They instead use smooth transitions of many 
> colors that gradually change from one point to the next.'

Color maps are linearly interpolated. And that does qualify as a "smooth 
transition", it is referring to the fact that colors are blended 
smoothly from one to the other instead of being bands of solid color, 
not to the change between blends.
I have often wondered whether it would be useful to have different 
spline types for color_maps, or to allow splines to be used as color 
maps(the xyz values would be taken as rgb values), but I never saw any 
real use for it...this is one I had missed.
One of the patches I have written should work for this specific problem, 
though: the "spline_wave" patch. It lets you specify (with a spline) the 
exact mapping the pattern goes through before evaluating the color_map, 
in other words, giving a custom waveform to the pattern...in this case 
you would use a single black-white gradient and adjust the spline_wave 
to get what you want. I don't know if it will make it into MegaPOV 0.6b, 
though.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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In article <3A53A995.2E42E153@gmx.de>, Christoph Hormann 
<chr### [at] gmxde> wrote:

> You can also try to specify a more detailed color_map using a #while loop
> for example.  

You could also make a macro (using MegaPOV's spline feature or a spline 
include file) to convert a spline to a color_map...just watch out for 
the 255-entry limit in the official version and current MegaPOV.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Thanks for the advice, chaps!

I'll have a go with a #while loop and a spline.

Bye.

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That's how it should be, the abrupt change is in the rate of change, not the
color itself.

--
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/

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