Povray creates height_fields between coordinates <0,0,0> and <1,1,1>.  The
precise location depends on the input value, so it will vary from scene to
scene. I have found it helpful to perform a translation first in order to
center the height_field upon the origin. So, after applyng your texture
perform a translation of "<-.5,-.5,-.5>." This will give you a much better
idea of "where you are."
  Next, the characteristic of height_fields to deteriorate under large
scalings can be countered by using large input images. When using Pov, to
create input, *always* use a global setting of "hf_gray_16," in order to
insure an accurate and smooth transition between points on the field. Read
that sentence again. :) I said to create input. You don't need it to create
your final image, and it won't come out right if you do. Remember, the
larger the input image, the better the result. Use gray values in the
creation of your input file, and you can very easily control the position
and height of your results.
  Next, about the horizon, it is usually best to use more then a single
input file, and thus more then a single height_field. Otherwise, in order to
avoid that workaround, place the camera closer to the terrain.
  Now, go over to povray.binary.images and look at the heading "HillBilly
DoorKnob." The door, and the brick wall are height_fields. They are not
perfect (nothing ever is), but the image demonstrates that success is
possible. For both objects, I created hf_gray_16 images to use as input. I
have already improved upon it, but I won't waste bandwidth on the subject.
If, however, you want the source, I will post it when I finish it (or tire
of it).
  Don't hesitate to write if you need more help, or if I haven't answered
all of your questions.

--
Paul Hinds
gri### [at] swbellnet

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