Jerry Stratton wrote:

> I've never seen coincident surfaces act like this. In the past, it has
> always chosen one or the other at (apparent) random to display (and when
> both are the same texture, it hasn't shown). So merge, rather than doing
> what union does and choosing one, just gives up and effectively clips the
> surfaces?
> 
> Is it my imagination that merge did not used to do this?

 I just tried it on the dos version of POV-Ray v2.2 and it acted the same.
The reason you are percieving it as a clipping operation is because the
merge operation removes all interior surfaces. In fact I would say that
you are lucky that the two boxes where they overlap are coming out so
clean. If it were a true coincident surfaces problem you would likely
see physical artifacts left over by the merge operation. As it is the
merge operation is simply removing all overlapping and interior surfaces
just like you would expect it to.

 In the example below you can see where I have learned to exploit this
feature of the merge function to create an open geometeric object. Also
not unusual use of the cone object which has a negative radius specified.

  #declare SnowTex = 
   texture {
     pigment { rgb 1 }
      finish { ambient .6
               diffuse .2
               specular 1
               roughness .001
               brilliance 2
               reflection .02
               crand 0.1
             }
           }

  #declare MB = union{
  cone{<0,0,0>,1.3,< 0, 1, 0>,-0.25 open}
  cone{<0,0,0>,1.3,< 0,-1, 0>,-0.25 open}
  cone{<0,0,0>,1.3,< 1, 0, 0>,-0.25 open}
  cone{<0,0,0>,1.3,<-1, 0, 0>,-0.25 open}
  cone{<0,0,0>,1.3,< 0, 0, 1>,-0.25 open}
  cone{<0,0,0>,1.3,< 0, 0,-1>,-0.25 open}}

  #declare Fk = merge{
  sphere{<0,0,0>,1.1}
  object{MB rotate  0*y}
  object{MB rotate 45*z}
  object{MB rotate 45*y}
  object{MB rotate 45*x}}

  object{Fk texture { SnowTex } scale 2 }

  light_source { <100,225,-200> rgb 1}

  camera{location<0,0,-9> look_at 0 }

-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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