Am 26.07.2012 16:02, schrieb Chaanakya:
> "Chaanakya" <nomail@nomail> wrote:
>> Warp <war### [at] tagpovrayorg> wrote:
>>> Chaanakya <nomail@nomail> wrote:
>>>> I was trying to create half of a hollow cylinder (both ends open).  I tried
>>>> using CSG with an intersection, and that gave me a half a hollow cylinder, but
>>>> I'd like to not have a plane on the end.  That is, I'd like essentially a curved
>>>> plane (the side of the cylinder without the endcaps).  Is there some
>>>> transformation I could use on, for example, a box to achieve this?
>>>
>>> Just make a difference of the cylinder and another cylinder with a slightly
>>> smaller radius and which is a bit longer ther the first cylinder.
>>
>> Thanks!  That lets me control the thickness of the resulting object.  How would
>> I cut it in half?
>>
>> - Chaanakya
>
> This is a bit weird....the shell seems way too thick when I render this:
>
> #version 3.6;
> #include "colors.inc"
>
> global_settings {
>    max_trace_level 256
>    ambient_light White
>    assumed_gamma 1.0
> }
>
> camera {
>    location <10,0,0>
>    look_at <0,0,0>
>    //rotate <0,0,-clock*90>
> }
>
> light_source {
>    <0,100,0>
>    color White
> }
>
> plane {
>    y, -10
>    pigment { hexagon Green, White, Blue }
> }
>
> difference {
>    cylinder { <-1,0,0>,<1,0,0>,1}
>    cylinder { <-1.00003,0,0>,<1.00003,0,0>,0.99999999}
>    pigment { color Red }
> }
>
> The shell should be barely visible, but it's quite thick.  Why?  Is it floating
> point error?

What you're seeing is just a perspective effect; change the camera 
location to e.g. <10,3,0> and light source position to e.g. <100,100,0> 
to better see what's goung on.

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