I'm putting this in the povray.newusers area because I suspect it may be a
question that only someone with limited knowledge of POV-Ray might find
themselves needing to ask.  I, however, have been using POV-Ray off and on
for quite a few years.  My first POV-Ray stuff was done back when it was a
DOS-based program.

That having been said, I'm having a very perplexing problem.  I'm trying to
make a planet with POV-Ray 3.6.  I create this humungous sphere with a
camera focused on it's edge at an extreme closeup.  At this point you can't
really tell that you're looking at a shpere; just like looking at the
horizon on Earth, everything is just flat and fades off in the distance.

Then I start moving the camera back to get a wider perspective.  It was my
intent to pick a position that would give me a view of the whole planet.  I
put my camera at -6E4 * z, then -6E5 * z, etc.  However, when I went to
-6E7, the planet completely disappeared!

To debug the problem, I set the distance at -6E6 (the last time I saw the
planet where it was supposed to be) and multiplied it by 2, 3, etc. to see
exactly where the planet disappears.  I found that the planet wasn't just
vanishing, it was dropping (downwards) out of the view.  But, my lood_at
value never changed!?!  My planet's position was never changed.  I don't
get it.

Below is the code that will demonstrate the effect.  If you increase the
Z_Multiplier value by increments of 0.2, you can watch the planet, step by
step, drop below the camera's view.  I don't want it to do that.

Can anybody tell me what is going on and, more importantly, what I can do to
fix it?

Thanks a bunch!

===== Code begins ======

// Vers: 3.5
// Desc: Basic Scene Example
// Date: mm/dd/yy
// Auth: ?
//

#version 3.6;

#include "colors.inc"

global_settings
{
   assumed_gamma 1.0
}

// ----------------------------------------

#declare View_WorldView = 1;
#declare View_CloseUp   = 2;

#declare SwitchView = View_WorldView;
//#declare SwitchView = View_CloseUp;

#declare Z_Multiplier = 2.0;

#declare CamPos_WorldView  = < 0.0,  0.0, -Z_Multiplier * 6E6 >;
#declare LookAt_WorldView  = < 0.0,  0.0, 0.0 >;

#declare CamPos_CloseUp    = < 0.0, 5.5, -12 >;
#declare LookAt_CloseUp    = < 0.0, 2.0, 0.0 >;

// ----------------------------------------

camera
{
   #switch ( SwitchView )
      #case ( View_CloseUp )
      location CamPos_CloseUp
      look_at  LookAt_CloseUp
      #break

      #case ( View_WorldView )
      location CamPos_WorldView
      look_at  LookAt_WorldView
      #break

   #end // of switch

   direction 1.5 * z
   right     x * image_width / image_height
}

// ----------------------------------------

background
{
   rgb < 0.6, 0.7, 1.0 >
}

// ----------------------------------------

light_source
{
   < 0, 0, 0 >            // light's position (translated below)
   color rgb < 1, 1, 1 >  // light's color
   translate < -30, 30000, -30000000 >
}

// ----------------------------------------

#declare PlanetaryRadius = ( 4000.0 * 5280.0 ); //3820.0;

#declare Water = false;

// The World
sphere
{
   0.0, PlanetaryRadius

#if ( Water )
   texture
   {
      pigment
      {
         color < 0, 0, 0 >
      }

      normal
      {
         bumps 0.03
         scale 0.2 //0.05
      }

      finish
      {
         reflection 0.7
      }
   }
#else
   texture
   {
      pigment
      {
         color rgb < 0.7, 0.5, 0.3 >
      }
   }
#end

   translate -PlanetaryRadius * y
}

// ----------------------------------------
==== End of code ====

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