Hey, gang.

To whomever it was who said he was a 3-year user and yet still a newbie, I
sympathize.  I've been mucking with POV since '97, and I still frequently go
back to my old scenes thinking, "Wait a second...  How do you define a light
source again?"  Okay.  I admit it.  I'm an idiot.

But anyway, I've noticed a problem with all of my height fields.  When I
zoom in on them, there are often white (or very light) patches on them that
don't make any sense to me.  I don't know if the weird shaping in spots
makes the traces skim over areas or if the normals at those parts are just
perfectly aligned with the light source to cause weird problems (actually,
moving the light source doesn't help, so that ain't it).  I'm just clueless,
but this makes it frustratingly difficult to create landscapes since these
spots don't look terribly realistic.

Anybody have any words of wisdom for this old newbie?
An example statement is below, and anyone would like to see image output (or
input), let me know; I just wasn't about to clutter the newsgroup with it
without being asked (and even then, should I post it in binaries?).

Thanks!

- m




// example height field possessed by demons of stupidity

height_field {
 sys "C:\mydocu~1\povfiles\height_field\rollinghills1.bmp"
 smooth
 translate <-0.5, -0.25, -0.5>
 scale <10, 4, 10>
 rotate -5*z
}

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A small example scene would help a lot.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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Small example scene...  Okay.  Try this.  The bmp can be found at
http://www.slimy.com/~mgreen/rollinghills1.bmp shortly.

// =====================================

camera {
 location 0.2*<11, 3, 0>
 look_at 0.2*<0, 2, 0>
}

light_source {
 <10, 3, -10>
 color 1.9*<1, 1, 1>
}

#declare ground_o =
 height_field {
  sys "C:\mydocu~1\povfiles\height_field\rollinghills2.bmp"
  smooth
  translate <-0.5, -0.25, -0.5>
  scale <10, 4, 10>
  rotate -5*z
 }

#declare ground =
 object {
  ground_o
  texture {sandtex}
 }

object {
 ground
}

#declare sandtex =
  texture {
     pigment {color rgb 1.34*<0.75,0.68,0.5>}
     normal {bozo, 0.8 scale 0.2}
     finish {crand 0.1 ambient 0.4}
  }

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... make that
http://www.slimy.com/~mgreen/rollinghills2.bmp

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Heightfields sometimes behave in strange ways which I haven't understood.
Sorry, but I have no ideas about this.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Hey there, Matthew.

Well, I didn't have any luck when I went to check this out. I even tried
making your bmp file into a png, output as hf_gray_16 with orthographic
camera to try and get the best possible heightfield. Same thing really, a
little different but same bad result.
Reason?: it's a 256 color, 8 bits/pixel image file. At least that would be
my guess as to why it doesn't smooth well enough. The normals on the surface
of the HF could be another matter, however when I create a hf_gray_16 output
using pigment {granite} and use it instead things are fine. Only scale
matters then as to how pixellated the result is, the normals appear fine.

Bob

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Hey Matthew,

What I think is happening, is that your heightfield is terraced (shaped like
steps) and your light-source is very close to the surface. This causes rays
from the light to hit the vertical edge of the terraces and not the tops of
them making the flat sides seem to glow white because your light source is
multiplied by 1.9. You can reduce the appearance of these white spots by
moving your light source higher in your scene. This however does not change
the fact that your heightfield looks like steps in profile.

Hope this answers your question,

J.N. Roy

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