"Slime" <fak### [at] emailaddress> wrote in message 
news:42044254$1@news.povray.org...
>> One of the bizarre effects was that
>> no matter what I did, the hole cut by the heightfield would extend all 
>> the
>> way through to the other side of the object.  It didn't seem to matter 
>> how
>> small I made the heightfield or how deep I made the box.
>
>
> By the way, are you aware that your height field surface is completely
> outside of the box's surface? This is why it cuts all the way through. 
> Since
> you're rotating it by -90 degrees in the x direction, it extends from Z = 
> 0
> backwards to Z = -0.5, whereas your box extends from Z = 0 to Z = 1. So
> everything in the box {0, <0.5, 0.5, infinity>} is cut away by the height
> field.
>


I think I understand what's going on now.  Originally, I had used a 
heightfield with "waterlevel".  Even though the heightfield appeared just as 
I expected, the difference operation was quite a bit different from what I 
had expected.  I tried to make an example based on that faulty bit of code. 
Simply rotating and translating (in order so "slice" from the other 
direction) seems to have fixed the problem.

I was not aware of the "infinity" aspect of heightfields.  I believed that 
they were contained within a box, which then led to my confusion.  Thanks 
for the "paradigm shift".  ;-)

This code below produces what I expected to see (though it's not the 
cleanest bit of code).

difference {
  box { 0, 1}
  height_field {
    png "hole.png"
    rotate x*-90
    scale 0.5
    translate z*1.2
  }
  rotate y*160
  pigment {Red}
}

-- 
Jeremy
www.beantoad.com

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