"Thorsten Froehlich" <nomail@nomail> wrote in message 
news:web.4dd3aa7c955938cce619b42c0@news.povray.org...
> Jim Holsenback <jho### [at] povrayorg> wrote:
>> On 05/18/2011 06:55 AM, Thorsten Froehlich wrote:
>> > "SGeier"<som### [at] somewherecom>  wrote:
[...]
>> >> In steps (2) and (3) I see the exact same thing that I see with the 
>> >> sphere
>> >> object. In particular I can see the shadow on step (3) that tells me 
>> >> that I
>> >> can see the inside/backside of the isosurface.
>> >>
>> >> But in step 4, the back/inside of the isosurface is gone.
>> >>
>> >> Why?
>> >
>> > Because you did not read the manual.
>> >
>> > See http://www.povray.org/documentation/view/3.6.1/300/
>> >
>> > Thorsten
>> >
>> >
>> >
>> hmmm ... I didn't spot the clue. I'm tempted to say the use of or size
>> clipper ... care to offer another hint ;-)
>
> The hint about CSG and isosurfaces is at the very end of that page ;-)
>
> Thorsten

*IF* you are making reference to this sentence:

  "By default POV-Ray searches only for the first surface which the ray 
intersects. But when using an isosurface in CSG operations, the other 
surfaces must also be found. Therefore, the keyword max_trace must be added 
to the isosurface statement. It must be followed by an integer value.

*THEN* I'd like to point out that this sentence is false:
- The back-side of the isosurface IS the first surface the ray intersects 
after the sphere is clipped.
- It is in fact found when the 'clipper' object is visible.

It only vanishes after I turn off the clipper object. Even though it is 
still the first surface of the sphere that the viewing-ray intersects 
(because all surfaces "in front of it" are clipped). Nothing has changed 
about the sphere or which of its surfaces should or should not be 
intersected by the viewing ray; all that has changed is that I made the 
clipper-volume invisible.

Of course there is no reason why 3.7 should conform to the 3.6 
documentation. Which makes it a bit disingenous to point people to the 3.6 
docs when they ask questions about 3.7 regarding behaviour *that is 
definitely in conflict with the 3.6 documentation*.

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