Hi all!

This is a project, i started some year ago. Now it's maybe worth posting.

<talking (too) much>
The oldest part is the thermometer itself. I once stopped working on it,
when the lathe-bug crossed my way (the dark line at the green capsule - it's
not jpeg...): I'm not that sure, what it is. In march '99 Ken discovered a
so called "media bug". But it was the "well known" lathe bug (thomas
willhalm answered). It's in povray.bugreports.
I don't know much about this bug, i guess it's a precision problem. Will
this bug be fixed in a next version? Or does a workaround exist? I realized
that the problem gets bigger when you decrease the camera-angle. It is
something with orthoganal hits on the lathe.

Than there was another problem. The problem of coincident surfaces. Try to
modell a hollow glassphere half-filled with water. I didn't know a way to
avoid the problem with coincident surfaces but a very difficult one (a union
of{ the glass and a difference of {a union of { a bigger water and
airpart }}cut out to fill the sphere} I know i can't describe it well, but I
can send you the source. (Thinking of it now, clipped_by would improve it)

The sky is the first skysphere ever made by my girlfriend.

On the floor (that is a table with (I know ) a bad wood texture) there is a
crochet work out of 11000 sphere - try to meet with reality. Sorry for the
'real' floor (simple hexagon) but i hoped jpg (compression 60%) would love
it.

And - yes, I know it's a huge format (somewhat 768*2304) but now you can see
the inscription on the weights.
Can someone of you tell me the physics of the thermometer - i once knew, but
having finished school a half year ago, I forgot all physics. :-(
What happens is, if it's getting warmer, the capsules sink onto the floor.
the lowest of the leaving swimming capsules tells the temperature (that is

</talking (too) much>

What do you think of the scene?

cukk

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Attachments:
Download 'thermo.jpg' (98 KB)

Preview of image 'thermo.jpg'

I like this a lot, although a smaller image in a *.png might have preserved the
caustics better, but nice.

The Gallilean (sp?) themometer work on density changes of the bulk fluid verses
the fludis in the bulbs. As the temperature rises, the density of a liquid
ideally is reduced. So, as the temperature rise the density of all the liquids
in the thermometer goes down (bulk liquid as well as each bulb), but what is
important is that the rate of change, dp/dT  (p = rho = density g*ml^-1), is
different for each liquid. I forget what the composition of each liquid is (each
bulb has a slightly different composition), but that is how they work.


-paul
-------------------------------------------#
Paul Daniel Jones
120 Chandlee Laboratory
Penn State University
814-865-2090
pdj### [at] psuedu

http://research.chem.psu.edu/glassgrp/paul
--------------------------------------------#

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The dark line at the horizon? Sturm?

Grim

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Arranging the floor backgroud and the table should give better looking
results...
-- 
+-------------------------+----------------------------------+
| Simon Lemieux           | Website : http://www.666Mhz.net  |
| Email : Sin### [at] 666Mhznet | POV-Ray, OpenGL, C++ and more... |
+-------------------------+----------------------------------+

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Hi Paul!

> I like this a lot, although a smaller image in a *.png might have
preserved the
> caustics better, but nice.

Could you point me to a good png-programm. I don't know how to convert to
png.

Thinking of the Gallilean thermometer: The main trick is, that the volume of
the water increases, if it's getting warmer. The density decreases, and now
the capsules or too heavy to swim. Their density doesn't count. The mass is
constant, the volumechange is to neglect.

cukk

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"KalleK" <kal### [at] gmxde> wrote in message news:3a003d96@news.povray.org...
>
> Than there was another problem. The problem of coincident surfaces. Try to
> modell a hollow glassphere half-filled with water. I didn't know a way to
> avoid the problem with coincident surfaces but a very difficult one (a union
> of{ the glass and a difference of {a union of { a bigger water and
> airpart }}cut out to fill the sphere} I know i can't describe it well, but I
> can send you the source. (Thinking of it now, clipped_by would improve it)

First of all, got to say that now I know someone made this before I ever got
around to starting on one.  But I won't let that stop me  :-)
About using clipped_by.  Big mistake, if I understood you, because I think the
unioned difference is best to get a correct CSG.  Since clipping leaves object
open it's not very conducive to refraction (ior), imo.  At least not for all
things.
I'd just scale a copy of the object being used in the final union as the
cutaway object a fraction larger or smaller (depending on the desired result).
The laced cloth is a nice touch.  You're own creation, or from a macro or
include file someplace?

Bob

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Hi Bob!

> About using clipped_by.  Big mistake, if I understood you, because I think
the
> unioned difference is best to get a correct CSG.  Since clipping leaves
object
> open it's not very conducive to refraction (ior), imo.  At least not for
all
> things.
Yes. When I thought about finally improving my source I realized it's not
that easy. Exactly that problem with refraction...

> I'd just scale a copy of the object being used in the final union as the
> cutaway object a fraction larger or smaller (depending on the desired
result).
But I think that this can cause some unwanted results with complex objects
(like the thermometer-lathe). If you scale the letter "H" his new 'volume'
will not cover the old one. The result would be surfaces of the cutaway
object in the final union. Therefore I used a much bigger cylinder for the
cutaway object.

> The laced cloth is a nice touch.  You're own creation, or from a macro or
> include file someplace?
It's my own creation. Some loops, no macros. It should match with reality
and represent the real crochet work the thermometer is placed on in reality.
In fact this detail encouraged me to finally post the scene.

As far as the lathe bug is concerned - i got no answers. Shell I ask in
povray.general? I want to avoid these artefacts and don't know how.

cukk

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"KalleK" <kal### [at] gmxde> wrote in message news:3a05920f@news.povray.org...
>
> As far as the lathe bug is concerned - i got no answers. Shell I ask in
> povray.general? I want to avoid these artefacts and don't know how.

I'm not so sure it can really be classified as a true "bug" since it's probably
more of a mathematics problem in the spline.  They tend to wrap back on
themselves if the points which are set up for the profile aren't in good
relation to one another.  sturm helps but can't seem to go beyond a certain
limit to clear it up.  Numerical precision and all that, you know.
Anyhow, what I'm actually getting at is that the spline calculations are either
faulty or just can't reach correct accuracy.  But if you place the points well
enough there wouldn't be artifacts.  What it needs is a over-ride to prevent
bad points and thus bad splines.  I guess in that respect it would be a bug
once the answer to that were found.
Didn't make perfect sense, did I ?

Bob

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Hi Bob!

> I'm not so sure it can really be classified as a true "bug" since it's
probably
> more of a mathematics problem in the spline.  They tend to wrap back on
> themselves if the points which are set up for the profile aren't in good
> relation to one another.  sturm helps but can't seem to go beyond a
certain
> limit to clear it up.  Numerical precision and all that, you know.
Now I get what Grimdude answered. And I thought it was a joke. Because sturm
is a german word for storm. And If there was a dark line at the horizon, it
could be a storm. but it's that keyword sturm, he ment. I see and will try
sturm now.

> Anyhow, what I'm actually getting at is that the spline calculations are
either
> faulty or just can't reach correct accuracy.  But if you place the points
well
> enough there wouldn't be artifacts.  What it needs is a over-ride to
prevent
> bad points and thus bad splines.  I guess in that respect it would be a
bug
> once the answer to that were found.
> Didn't make perfect sense, did I ?
Reading twice helped (but that are maybe language problems to be solved...)

Now I'm disappointed - I thought I prevented the spline from bad points,
therefore i did a cubicspline-prism first.
And having tried to find out what was wrong, I realized the error on the
lathe was exactly the height of the camera (those orthogonal rays to the
lathe, Thomas Willhelm mentioned in his answer to kens so called "media bug"
in march '99).
You answer is another direction, and i thought i had no "bad points" in the
lathe spline. Have to look at it.

Anyway, many thanks to you(r help)!

cukk

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I don't generally reply in German (my Deutsche being so poor).

Grim

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