Hello everyone, I hope this is the correct group.  My apologies if it is
not.

I am having some difficulty with rendering heightfields (pov and megapov do
the same thing).  I am getting a "patchiness" large patches on slopes that
do not conform to anything reasonable as seen in this small are of an image.
I've eliminated everything in the scene except the heightfield (feed by an
image) and shaded with White.  I've tried other height map images, and
everything exhibits the same symptoms.

The problem is the dark gray patches creeping up the slope of this plateau
which are clearly not conforming to the true shape.  In heightfields with
gentle hills, I get the same thing (even more prominent).

Any hints?

Thanks,

David Whatley
dw### [at] playnet


ps. POV is a wonderful work of engineering.  Kudos to those who made it
possible!

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Attachments:
Download 'test.bmp.dat' (25 KB)

David Whatley wrote:
> 
> Hello everyone, I hope this is the correct group.  My apologies if it is
> not.
>
> I am having some difficulty with rendering heightfields (pov and megapov do
> the same thing).  I am getting a "patchiness" large patches on slopes that
> do not conform to anything reasonable as seen in this small are of an image.
> I've eliminated everything in the scene except the heightfield (feed by an
> image) and shaded with White.  I've tried other height map images, and
> everything exhibits the same symptoms.
> 
> The problem is the dark gray patches creeping up the slope of this plateau
> which are clearly not conforming to the true shape.  In heightfields with
> gentle hills, I get the same thing (even more prominent).
> 
> Any hints?

How big is the image you are using for the HF object? If it is a low
resolution image you often see a gridding effect because there are
much fewer pixels worth of information for POV-Ray to work with. Higher
resolution (640x480 or larger) images often give better results.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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Hi

I have found that in addition to Ken's suggestion, adding a normal will
solve the problem.

Mick

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David Whatley wrote:
> 
> Hello everyone, I hope this is the correct group.  My apologies if it is
> not.
> 
> I am having some difficulty with rendering heightfields (pov and megapov do
> the same thing).  I am getting a "patchiness" large patches on slopes that
> do not conform to anything reasonable as seen in this small are of an image.
> I've eliminated everything in the scene except the heightfield (feed by an
> image) and shaded with White.  I've tried other height map images, and
> everything exhibits the same symptoms.
> 
> The problem is the dark gray patches creeping up the slope of this plateau
> which are clearly not conforming to the true shape.  In heightfields with
> gentle hills, I get the same thing (even more prominent).
> 
> Any hints?
> 

I can't say much from this small picture.  If you are using 'smooth' try
turning it of and see the result, it usually gives a better impression of
the geometry and resolution which is not changed by smooth BTW.

Otherwise a larger perspective view (preferred in jpg) and maybe the code
could help.

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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"Mick Hazelgrove" <mic### [at] mhazelgrovefsnetcouk> wrote in message
news:3a839924@news.povray.org...
> Hi
>
> I have found that in addition to Ken's suggestion, adding a normal will
> solve the problem.
>
> Mick
>
>

I'm sorry, my limited experience with POV must be showing.  I was under the
impression that there were normals on the resulting mesh.  If not, it would
not generate any of it accurate, right?   What would the syntax be for
adding a normal?

For reference, here is the code and I've attached a more pathological
example:

#include "colors.inc"
  camera{
    location <-.7, 1, -7>
    look_at 0
    angle 45
  }

light_source{ <1000,1000,-1000> White 1.5 }

background {color <0.2,0.25,0.42>}

height_field
{
  png  "devils_tower_WY.png"
  smooth
  translate <-.5, 0, -.5>

  scale <15,1,15>

  pigment { White }
}

I've highlighted one of the areas with a red circle just to be clear (though
I don't believe it's not visible).  As you can see the terrain is properly
rendered except for these odd quad patches that have, what appears to be, an
incorrect normal.  Around it, though, are finely detailed hill slopes that
are fine in all respects.  What I don't it is... if I'm doing something
wrong here, why isn't it uniformly wrong?

Thanks for helping with this everyone. :)

David Whatley
dw### [at] playnet

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Attachments:
Download 'hfield.jpg' (15 KB)

Preview of image 'hfield.jpg'

Oh, and here is the source image in case it is helpful for reproducing the
problem.

David Whatley
dw### [at] playnet

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Attachments:
Download 'devils_tower_WY.png' (107 KB)

Preview of image 'devils_tower_WY.png'

David Whatley wrote:
> 
> "Mick Hazelgrove" <mic### [at] mhazelgrovefsnetcouk> wrote in message
> news:3a839924@news.povray.org...
> > Hi
> >
> > I have found that in addition to Ken's suggestion, adding a normal will
> > solve the problem.
> >
> > Mick
> >
> >
> 
> I'm sorry, my limited experience with POV must be showing.  I was under the
> impression that there were normals on the resulting mesh.  If not, it would
> not generate any of it accurate, right?   What would the syntax be for
> adding a normal?
 
> For reference, here is the code and I've attached a more pathological
> example:
 
Adding a normal is easy to add and gives you a lot of options to work
with. Any pattern that works as a pigment also works within a normal
statement. I tested this example with the .png you sent me and it
effectively removed the problem you were seeing (although I did go
a bit overboard with it - YMMV).

See below for a simple example -

 height_field
 {
   png  "devils_tower_WY.png"
   smooth
   translate <-.5, 0, -.5>

  scale <15,1,15>
 
   pigment { White }
     normal { granite 1 scale .5 }

 }

-- 
Ken Tyler

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David Whatley wrote:
> 
> Oh, and here is the source image in case it is helpful for reproducing the
> problem.
> 

The problem is your heightfield file, don't know how you generated it, but
it contains 'lower lines' between the different seperated levels of height
(see attachment)

I tried to apply a smoothing filter to weaken that effect but you should
better use a geographically correct heightfield.  

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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Attachments:
Download 'image1.png' (7 KB)

Preview of image 'image1.png'

As a side note, can you have the height_field self-shadow?  It doesn't seem
too by default unless I'm doing something (else) wrong. :)

David Whatley
dw### [at] playnet

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David Whatley wrote:
> 
> As a side note, can you have the height_field self-shadow?  It doesn't seem
> too by default unless I'm doing something (else) wrong. :)

Add a finish statement :)

-- 
Ken Tyler

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