Surprising the difference 0.00001 makes.
I knew about that for punching holes through objects, but I didn't for 
intersection.
Many thanks.       Bob
"Jan Dvorak" <jan### [at] centrumcz> wrote in message 
news:480a2d1c@news.povray.org...
> Bob Frew napsal(a):
>> Am not really a newbie, thought I had CSG sussed.  However !!!
>> Can not see the reason I get a hollow object from the following code. See 
>> attached picture
>> All help appreciated
>> Bob
>>
>> #############################################################################
>> #version 3.6;
>> #include "colors.inc"
>> global_settings { assumed_gamma 1.0}
>> // ----------------------------------------
>> #local cam_type = "t";
>> #if (strcmp(cam_type, "f") = 0)  // f = from front
>>      #local cam_location = <0.0, 0.5, -3.0>;
>>      #local cam_look_at  = <0.0, 0.5,  0.0>;
>> #end
>> #if (strcmp(cam_type, "t") = 0)        // t = from top
>>      #local cam_location = <0.0, 4.5, -0.1>;
>>      #local cam_look_at  = <0.0, 0.0,  0.0>;
>> #end
>> camera {
>>   direction 1.5*z
>>   right     x*image_width/image_height
>>   location  cam_location
>>   look_at   cam_look_at
>> }
>>
>> sky_sphere {
>>   pigment {
>>     gradient y
>>     color_map {
>>       [0.0 rgb <0.6,0.7,1.0>]
>>       [0.7 rgb <0.0,0.1,0.8>]
>>     }
>>   }
>> }
>> plane { y, 0
>>         pigment { checker
>>                 pigment { color rgb <0.7,0.0,0.0> }
>>                 pigment { color rgb <1.0,1,1> } }
>>   }
>> light_source {<0, 0, 0> color rgb <1, 1, 1>  translate <-0.1, 100, -0.2>}
>> light_source {<0, 0, 0> color rgb <1, 1, 1>  translate <-5, 5, -0.2>}
>> // -------------------------------------------------------------------
>> intersection {
>>     cylinder { <0, -1, 0>, <0, 1, 0>, 1 translate -0.5*x }
>>     cylinder { <0, -1, 0>, <0, 1, 0>, 1 translate  0.5*x }
>>     pigment  { Yellow }
>>   }
>>
>> ############################################
>>
>>
>>
> Make one of the cylinders slightly longer. POVray does not know how to 
> handle coincident surfaces. This is a common problem of all or nearly all 
> raytracers.

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