Hello!

I have got a problem about fog and I'm almost desperate because I don't find any
solution.
The problem is that the ground_fog object doesn't appear on my rendered images.
The camera is not inside a solid object, so this should not be the problem.
I have got a few solid objects in the center, a sky_sphere object, a camera and
a light source. Nothing special.
I also copied codes from fog-objects from similar codes that worked, but also
that did not help.
Maybe you have got an idea, what could be the problem.
I would be very glad about that.
Thank you in advance!

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1.  What version of POV-Ray are you using?
2.  It's easier (and even possible) to help if you post a complete scene so we
can see exactly what is going on.
3.  Have you looked at
http://www.f-lohmueller.de/pov_tut/interior/interior_001e.htm   ?

Media can be tricky.

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Am 24.04.2016 um 22:52 schrieb Dedus:

> I have got a problem about fog and I'm almost desperate because I don't find any
> solution.
> The problem is that the ground_fog object doesn't appear on my rendered images.
> The camera is not inside a solid object, so this should not be the problem.
> I have got a few solid objects in the center, a sky_sphere object, a camera and
> a light source. Nothing special.
> I also copied codes from fog-objects from similar codes that worked, but also
> that did not help.
> Maybe you have got an idea, what could be the problem.

I have a few ideas, but as Bald Eagle already mentioned, without looking
at your scene code there's no way of knowing which of these is the case:

- Despite your claims, you might have a non-`hollow` huge object inside
your scene after all.

- Your ground_fog might be too thin to be noticeable.

- Your ground_fog might be engulfed by a huge object without a `hollow`
statement.

- Your ground_fog might be too dense to see anything but the fog, and
you might be mistaking the fog for background.

- Did I mention huge non-`hollow` objects yet?

- Your ground_fog altitude settings might happen to place the fog too
low to rise above your ground plane.

- You really should double-check once more for any huge objects
engulfing the scene and not carrying a `hollow` statement.


The reason I keep mentioning large non-`hollow` objects is that it's
probably the number one cause for media or fog to fail completely and
leave you puzzled -- and there are ways to immerse your scene in such an
object without it being glaringly obvious:

- You might have decided to use a very large sphere instead of a
sky_sphere, and forgotten about it.

- You might have accidently gotten the ground plane's direction vector
the wrong way round. Remember that a plane technically _is_ a solid
object, dividing the universe into an "inside" and "outside", even
though normally you don't see a difference.

- You might have accidently defined some other object inside-out. Like
with an upside-down ground plane, you won't normally see a difference.

- You might have a mesh in your scene that happens to be not perfectly
closed, and with an inside_vector that happens to point straight from
the camera to the "hole"; in that case, too, the camera would be
considered "inside" the mesh, knocking out the ground fog entirely.

If in doubt, add a `hollow` statement to _each and every_ object in your
scene; there's absolutely no downside to it (except if you're
intentionally using any objects to knock out media or fog in particular
places).

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clipka <ano### [at] anonymousorg> wrote a lot of great stuff:

Whoa.  That's a very interesting list of stuff.
Very educational.   I would have never thought of, and therefore never caught
several of those.

Sometimes I'd love to see a thread - or a section of the documentation - be
devoted to showing how SDL can get buggy or do unexpected things, and how best
to avoid or unravel it.

I'm curious if there's a way to determine if the media is inside an object, or
the camera is inside the mesh you mentioned.  Is there an inside/outside test
that can return a value?

Something like isenclosed(myObject) would be mighty handy.
It could return yes/no true/false, or the type of object that it is "most
directly" inside.  (if MySphere were in a box that was in a cylinder,
isenclosed(MySphere) would return "box".
I'm sure that's one of those things that's nearly impossible to do.

There's still SO much I don't know about what can and can't be done in POV-Ray.

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> clipka <ano### [at] anonymousorg> wrote a lot of great stuff:
>
> Whoa.  That's a very interesting list of stuff.
> Very educational.   I would have never thought of, and therefore never caught
> several of those.
>
> Sometimes I'd love to see a thread - or a section of the documentation - be
> devoted to showing how SDL can get buggy or do unexpected things, and how best
> to avoid or unravel it.
>
> I'm curious if there's a way to determine if the media is inside an object, or
> the camera is inside the mesh you mentioned.  Is there an inside/outside test
> that can return a value?
>
> Something like isenclosed(myObject) would be mighty handy.
> It could return yes/no true/false, or the type of object that it is "most
> directly" inside.  (if MySphere were in a box that was in a cylinder,
> isenclosed(MySphere) would return "box".
> I'm sure that's one of those things that's nearly impossible to do.
>
> There's still SO much I don't know about what can and can't be done in POV-Ray.
>
>

If you wrap your whole scene, minus the camera, into an union, you can 
make an insideness test on that union from the camera's location.
If the result is zero (no/false), the camera is outside all of the 
scene's objects. If the result is one (on/true), then the camera is 
inside something, but you don't know what object.
There is no way that I'm aware of that can directly return whitch object 
you are inside of. For that, you need to declare all objects, translate 
them to the final location, then, in a loop, individualy test your point 
against all of the objects of your scene.




Alain

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> Hello!
>
> I have got a problem about fog and I'm almost desperate because I don't find any
> solution.
> The problem is that the ground_fog object doesn't appear on my rendered images.
> The camera is not inside a solid object, so this should not be the problem.

Are you sure? Check the message pane after the render is completed. If 
you get a warning mentioning the camera and non-hollow object, then your 
camera is realy inside some object.

> I have got a few solid objects in the center, a sky_sphere object, a camera and
> a light source. Nothing special.

A sky_sphere is not an object at all, but a background feature. If your 
sky_sphere is realy an object instead of a background feature, then you 
need to add hollow to it.

> I also copied codes from fog-objects from similar codes that worked, but also
> that did not help.
> Maybe you have got an idea, what could be the problem.
> I would be very glad about that.
> Thank you in advance!
>
>

Do you use an actual sky_sphere, a very large sphere, or some sky_sphere 
generating macro?
The sky_sphere is a background feature and don't have any inside.
A very large sphere definetely have an inside, and everything in the 
scene is inside that sphere. You need to add hollow or inverse to that 
sphere.
A macro may actualy create a very large sphere. Enclose that macro into 
an object statement : object{SkySphereMacro() hollow}




Alain

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