 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Is there a way to use a fog-like command to kill all rays over a certain length?
Rather than the exponential decay with length with a normal fog, I would like
any ray over a certain length to be entirely eradicated, and any ray shorter
than that to be transmitted, possibly with a slight fuzziness between these two
extremes.
Any ideas?
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
"statto" <nomail@nomail> wrote:
> Is there a way to use a fog-like command to kill all rays over a certain length?
>
> Rather than the exponential decay with length with a normal fog, I would like
> any ray over a certain length to be entirely eradicated, and any ray shorter
> than that to be transmitted, possibly with a slight fuzziness between these two
> extremes.
>
> Any ideas?
I think bounding boxes work in a similar manner. Not sure though.
-Mike
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
statto nous illumina en ce 2008-12-10 07:22 -->
> Is there a way to use a fog-like command to kill all rays over a certain length?
>
> Rather than the exponential decay with length with a normal fog, I would like
> any ray over a certain length to be entirely eradicated, and any ray shorter
> than that to be transmitted, possibly with a slight fuzziness between these two
> extremes.
>
> Any ideas?
>
>
There is no ready, automated, way to do that. I'm not sure why you want that.
What you can do:
Enclose your scene within a large sphere centered at the camera. That sphere's
radius is set to the distance at whitch you want your rays terminated. Be sure
to make it hollow, or use the "inverse" key word, if you want to use some fog.
Use one of the background feature, and make sure that there are no object
farther than the maximum distance you want. You may put your scene into an
union, and intersect it with a large sphere. Anything outside that sphere will
be removed.
SarkD, bounding box don't work that way. Bounding boxes are used to make ray
intersection tests with objects more efficient. You test against the list of
bounding boxes, and, if you hit one, you test the object within.
--
Alain
-------------------------------------------------
A modest man is usually admired; if people ever hear of him.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Alain <ele### [at] netscape net> wrote:
> statto nous illumina en ce 2008-12-10 07:22 -->
> > Is there a way to use a fog-like command to kill all rays over a certain length?
> >
> > Rather than the exponential decay with length with a normal fog, I would like
> > any ray over a certain length to be entirely eradicated, and any ray shorter
> > than that to be transmitted, possibly with a slight fuzziness between these two
> > extremes.
> >
> > Any ideas?
> >
> >
> There is no ready, automated, way to do that. I'm not sure why you want that.
>
> What you can do:
> Enclose your scene within a large sphere centered at the camera. That sphere's
> radius is set to the distance at whitch you want your rays terminated. Be sure
> to make it hollow, or use the "inverse" key word, if you want to use some fog.
>
> Use one of the background feature, and make sure that there are no object
> farther than the maximum distance you want. You may put your scene into an
> union, and intersect it with a large sphere. Anything outside that sphere will
> be removed.
>
>
> SarkD, bounding box don't work that way. Bounding boxes are used to make ray
> intersection tests with objects more efficient. You test against the list of
> bounding boxes, and, if you hit one, you test the object within.
>
> --
> Alain
> -------------------------------------------------
> A modest man is usually admired; if people ever hear of him.
Explaining why might make my question clearer: some friends and I were
discussing what it would look like if you could take a film with a camera so
fast that you could watch the progress of light across a room. I want the light
to ooze slowly out of the lights and over objects, and so I want to terminate
any ray which is longer than a distance ct, where c is the speed of light and t
the (short!) time since the start of the film.
If I understand your union-with-an-inverse-sphere suggestion correctly, it will
destroy all objects greater than a distance ct from the camera, which is not
quite the intended effect!
Perhaps my idea is impossible with POV-Ray...but I thought it would be easier to
make a computer model than try to do it in real life. ;)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
statto wrote:
> Explaining why might make my question clearer: some friends and I
> were discussing what it would look like if you could take a film with
> a camera so fast that you could watch the progress of light across a
> room. I want the light to ooze slowly out of the lights and over
> objects, and so I want to terminate any ray which is longer than a
> distance ct, where c is the speed of light and t the (short!) time
> since the start of the film.
I think there is a fundamental problem with this approach,
namely that POV-Ray does not trace from the light sources
forward but from the eye backwards. So, terminating rays
doesn't really have the effect of light oozing anywhere.
What you might do however, is to create an animation with a
light source which increases in range (using rather drastic
settings for fade_distance and fade_power, you should be
able to get sharp cutoffs).
Although this may look similar to what you expect, it is
however not physically correct because it does not take into
account the time for the light to travel from the object to
the camera.
Furthermore, you may also need to take into account that
your film material moves at relativistic speed :-P
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
"statto" <nomail@nomail> wrote:
> Explaining why might make my question clearer: some friends and I were
> discussing what it would look like if you could take a film with a camera so
> fast that you could watch the progress of light across a room. I want the light
> to ooze slowly out of the lights and over objects, and so I want to terminate
> any ray which is longer than a distance ct, where c is the speed of light and t
> the (short!) time since the start of the film.
I suggested a while back that a "speed_of_light" parameter be added to povray,
and the response was rather negative due to the required modeling of
relativity.
-Mike
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Alain <ele### [at] netscapenet> wrote:
> SarkD, bounding box don't work that way. Bounding boxes are used to make ray
> intersection tests with objects more efficient. You test against the list of
> bounding boxes, and, if you hit one, you test the object within.
Sorry, I just kind of read the thread title and skimmed over the rest of the
post.
-Mike
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
"SharkD" <nomail@nomail> wrote:
> > Explaining why might make my question clearer: some friends and I were
> > discussing what it would look like if you could take a film with a camera so
> > fast that you could watch the progress of light across a room. I want the light
> > to ooze slowly out of the lights and over objects, and so I want to terminate
> > any ray which is longer than a distance ct, where c is the speed of light and t
> > the (short!) time since the start of the film.
>
> I suggested a while back that a "speed_of_light" parameter be added to povray,
> and the response was rather negative due to the required modeling of
> relativity.
I remember an article *somewhere* about relativistic effects with an experiment
someone made with - ta-daaa - a modified version of PoV-ray!
So it must exist somewhere out there already...
The experiment showed the classic 3D-teapot zooming past the camera at about the
speed of light, and the PoV-ray version was tweaked to take speed of light into
account.
Much to the surprise of the readers (and possibly the experimentor as well), the
teapot did *not* look "squished" as is often claimed in popular-science articles
about relativity, but rather *rotated*!
Geez, if only I could remember where that article was! c't maybe (a german
computer technology magazine). I'll try to dig that up.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
"clipka" <nomail@nomail> wrote:
> Geez, if only I could remember where that article was! c't maybe (a german
> computer technology magazine). I'll try to dig that up.
Got something here (though it's not the original article I remember) on a German
web page for teachers:
http://www.lehrer-online.de/dyn/bin/435242-437415-1-programme_rel_raytracing.zip
The same page (http://www.lehrer-online.de/povray-relativistisch.php) claims
that there is also some Unix version downloadable from some university in
Australia, but that link seems dead.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
"clipka" <nomail@nomail> wrote:
> I remember an article *somewhere* about relativistic effects with an experiment
> someone made with - ta-daaa - a modified version of PoV-ray!
>
> So it must exist somewhere out there already...
I wonder how these modifications impacted performance, or whether they were
limited in such a degree that they were only in use when the designer intended
them to be.
-Mike
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
