-"According
to the tradition of the Physiologus and medieval
bestiaries,
the aspidochelone is a fabled sea creature, variously
described as a large whale or sea turtle."
-"It rises to
the surface from the depths of the sea,
and entices unwitting sailors to make landfall on its
huge shell. In the moralistic allegory of the Physiologus
and bestiary tradition, the aspidochelone represents
Satan, who deceives those whom he seeks to devour."
Hello World Introduction to Bullet
(Open Source - BULLET PHYSICS LIBRARY, Physics Symulation
Forum)
Sep 14, 2008
>>"Dropping
a ball that's 2cm wide from one meter high is like saying
you're dropping a ball fifty times its own width from the
ground"
- Chunky,
could you please explain what does that mean?
>>"Is that what you're doing too, or
are you dropping a basketball from waist height?"
- I think SynVis was pretty clear on what kind
of ball and what height, even supplied a listing where we
can see exactly what is he trying to do.
..it is recommended to
have meters as distance unit and than you should have
mass in kg not grams, but that shouldn't make any
difference with free fall. In any case units do not
matter much, it is about proportions and relations, but
it might help to have units sorted out especially if you
compare results with real life experiments.
In any case you should be able to enlarge your ball to
the minimum size of 0.2meters without any impact on
physics calculations because air resistance is not
directly implemented in Bullet, but also be sure to take
that lack of air resistance into account when comparing
with real life experiment.
Sep 14, 2008
>>"Well,
it's a question of perception. If you look at the big
ball on-screen, it drops really fast because 1) It
doesn't actually have as far to go; it hits the ground
much sooner because it's much wider, in absolute terms 2)
It doesn't appear to have as far to go because you're
only dropping it three times its own width, while the
smaller one has maybe fifty times its own width to fall.
Gary (-;"
Do you mean to say - "distance should be measured not from the centre of the ball, but from the lowest point" ?
>>"..big
ball on-screen, it drops really fast because.."
- Without air friction acceleration of small
objects is the same as big ones."
>>"..it
hits the ground much sooner because it's much wider, in
absolute terms"
- It hits the ground sooner only if you measure
the "distance" from the centre of the ball.
Don't do that, because that is not a real distance you
want to measure. "
Everything
is relative, "only Sith deal in absolutes"
For instance, If you move camera away - the big ball you
were talking about ain't so big anymore and it shouldn't
fall any "slower" just because we moved camera
around.
Problem When Increasing Gravity
(Open Source - BULLET PHYSICS LIBRARY, Physics Symulation
Forum)
Sep 20, 2008
>>"If
I just multiply all my object units by 50 to get them
into to 0.2 to 5 unit range then no problem there.
However, to make my objects move realistically, I would
have to multiply gravity by 50 too and that's where the
problem lies."
- Why do you think that you would need to
increase gravity?
When Appolo 15 astronaut Dave Scott let go of the feather and hammer they fell down with about the same speed and touched the Moon surface about the same time.
Size does not matter, mass matters but you can leave the mass out too if your objects are smaller than mountain i suppose. With all that said, gravity is actually pretty much unexplained really.
Sep 22, 2008
>>"Ignore
steven.hutheir; he seems to have not understood the
question."
- Sparkprime,
Exscuse me? Can you explain your statement?
>>"..you
will have to increase the simulation frequency I think
- I'm afraid that it is you who does not
understand. On the contrary, he needs to *decrease*
simulation frequency, i.e. to increase fixedTimeStep.
Practically, change your stepSimulation() call to one of
these:
1.)
stepSimulation(dt, 100, 1.0f/30);
2.) stepSimulation(dt, 100, 1.0f/10);
3.) stepSimulation(dt, 0);
Please report the results so that everyone can learn from their mistakes.
Thank you
Sep 22, 2008
>>"Ok,
I'll give a concrete example of why you *do* need to
increase gravity, real simple."
- I simply can't believe what is going on?
How do you two find appropriate to be giving any advice
if you do not know basics of Physics?
RobW,
You simply must be wrong,
because if you measure gravity anywhere on the Earth
surface you will read around ~9.8. Maybe if you simulate
'Black Hole', then you would have increase in gravity,
according to popular theories. I don't even dare to read
how you managed to "explain" your statement,
its just wrong to begin with.
Hopefully, someone will come along and clear it up. I will happily admit if im wrong.
Sep 22, 2008
>>"How
is anyone going to clear it up when you won't read a
concrete example?"
Huh?
>"because if you measure gravity
anywhere on the Earth surface you will read around
~9.8"
This is going to be very silly discussion if you are unable to understand that, in computer simulation, we are trying to "imitate" the above fact - meaning, we actually want gravity to be constant, just as it is in a real life, ok?
Sep 22, 2008
>>"Surely
you can take a little time out from being a general
physics genius to point out my mistake?"
- I do have time because i find it amusing.
Basically, you only have to read my 1st message, at least
once. Anyway, here we go again - look at the last
sentence starting with "because", its a 3rd
time now.. told you its gonna be silly.
>"because if you measure gravity anywhere on the Earth surface you will read around ~9.8"
Sep 22, 2008
>>"Yeah,
gravity measured near the earth's surface is ~9.81
ms/s/s, well done, but that was never in question. This
is the situation that we are actually talking about.
Spuddy is making a game where the objects are small in
metre units. Let’s pretend it's a pool game..."
Nonsense, are you actually the same person as "Sparkprime"?
There should be age limit or something. Are you not aware how much time you can waste by giving a bad advice? I hope you're not doing this on purpose or as some kind of a bad joke.
Is this a joke?
Sep 22, 2008
>>"..you're
actually starting to sound like a bit of an idiot."
- Spuddy, that's not very nice thing to say.
You did not mention what were the results with what I
suggested
So all three
of you are actually one and the same person?
You pose question, then answer it yourself with another
nick-name and got angry because someone interfered?
I don't see other explanation, it is impossible that three different persons would have this same understanding, especially if the one actually posed the original question, and then get angry for no apparent reason.
>>"If
you can't see this and acknowledge it then I'd prefer
that you didn't reply to this thread as I'd like to find
a solution, not argue with you over my
requirements."
- You see,
you say "not argue with you", but
"Spuddy" we never had an argument - I only had
an argument with your other two nick-names.
What is it you think you're doing?
Sep 22, 2008
>Please
report the results so that everyone can learn from their
mistakes.
>>"Well, I'm a
reasonable person, so I tried your suggestions. Now I'm
reporting back the results. Let’s just say, it wasn't
good.. "
- RobW, I
was asking "Spuddy", not you,
obviously all of you are making a 'pool game' and have
the same, wrong understanding and in the same time all
three of you are quite passionate about defending the
same wrong position, even more "Spuddy" that
actually asked the question in the 1st place is now
absolutely sure in his understanding, and for some reason
everyone still has the same problem.. sheesh!
Sep 22, 2008
>>"Please stop heating this flamewar, steven.hutheir"
>>"You
can also consider discussing this on IRC,
any freenode server channel #bulletphysics"
>>"Indeed,
when using a different scale..
you have to use a matching scale for gravity too."
- Erwin,
Can you please explain in what relation is size and
gravity?
Thank you
Sep 22, 2008
There
are two problems:
1.)
stepSimulation(dt, 0) will
solve moon-like slow downs, if not your computer is
simply too slow.
2.)
Everyone should understand that 3m ball will fall with
the same speed/acceleration as 15cm ball (no air
friction), and so the normal sized, real life pool table
will play just as same as 10x enlarged. Of course, mass
should stay the same as in real life pool table.
You should not increase gravity if you need to change the size of the balls.
What physics equation has both gravity and size?
Sep 22, 2008
>>"I
would urge you not to use this, and instead stick with
erwin's suggestion of
stepSimulation(dt, 100,
btScalar(1.0)/btScalar(240.0))"
- Chunky, please,
two of us already had this same discussion, it turned out
you too lack the basic knowledge in physics. I'm talking
about DIAGNOSTICS. If you're experiencing slow-downs,
then the first thing you need to check if your computer
is too slow, right?
Do you not
understand that by increasing the frequency you only
making it worse? You only need to look at the source code
to realize that:
//*** clamp the
number of substeps,
//*** to prevent simulation grinding spiralling
down to a halt
int clampedSimulationSteps =
(numSimulationSubSteps > maxSubSteps)? maxSubSteps :
numSimulationSubSteps;
for (int i=0;i<clampedSimulationSteps;i++)
{
internalSingleStepSimulation(fixedTimeStep);
synchronizeMotionStates();
}
Obviously
problem is still there as no one cares to realize that I
was right all along. Feel free to prove me wrong by
presenting just one Physics equation that has gravity and
size together.
By increasing the gravity you only introduce the
problems, then you try to fix them by doing the
completely opposite of what you should. You failed to
realize that you have TWO problems. If you look at the
source code you should understand that by increasing the
frequency you increase the number of iterations and if
your CPU was slow to begin with it explains all the
problems you're having.
>>"If
you are scaling your objects / world, please follow the
suggestions found here: Scaling The
World.
[www.bulletphysics.com/..php?title=Scaling_The_World]"
- According to all the reasons i already stated
in my 1st message that page is simply wrong, I don't know
about the rest but this bit is wrong - "Scale
gravity by X"
Size does not matter, I'm not sure why famous Apollo 15 experiment is not sufficient to prove that to this thread, it was enough of a "proof" for the rest of the world.
NASA -
Motion of free falling objects (no air resistance):
- "The weight, size, and shape of the
object are not a factor in describing a free fall"
Size does not matter.
Sep 23, 2008
>>"If
I increase the scale of my world so that the object now
has 1000 meters to fall and is.."
- I see now what is everyones problem.
You don't really know what is it your are talking about
when you say "scale my world"
You do not need to "scale" anything, all you need is to ENLARGE your OBJECTS, so that minimum sized shape is 0.2meters in size. Mass and everything else should stay the SAME as in real rife, INCLUDING GRAVITY.
But Chunky this might be a 3rd time I'm explaining this to you. All you have to do to prove me wrong is to find a piece of source code In Bullet where the acceleration of the objects caused by gravity is dependent of size. I'm not flaming I'm giving you the facts. Check it up on the internet.
I find it interesting that it was me who was accused of flaming, even thought they called me "idiot" and were suggesting that I should be ignored, and somehow different people all came up with the same understanding, logging one after another in a matter of minutes, being angry at me for no apparent reason. Funny.
*** messages DELETED, banned ..y'$#%@! ***
Scale in centimeters, need clarification
(Open Source - BULLET PHYSICS LIBRARY, Physics Symulation
Forum)
Oct 7, 2008
>>I'm
trying to get Bullet working for a simulation where my
real life object counterparts are measured in
centimeters, and the issue with 0.2 (meter) unit
precision is giving me major pains."
>>REFERENCING
PREVIOUS THREAD, PERSON EXPLAINS - HAS ALL THE SAME
PROBLEMS AS ALREADY DESCRIBED, only this time its CHESS
PIECES not POOL BALLS..
(UNSPOKEN:
huh?! ..could you be Fenrisulfr, again? what is going on,
deceiving people on purpose?!)
>>"Despite
my basic questions,
I'm actually pretty well educated in engineering and
computer science.."
(UNSPOKEN:
mhhh.. its time for magic mirror)
[..//..]
>>"..same problems, too. I
haven't yet found a series of parameter values that
work."
1.) When Apollo 15 astronaut Dave Scott let go
of the feather and hammer they fell down with about the
same speed and touched the Moon surface about the same
time. Size does not matter, mass matters but you can
leave the mass out too if your objects are smaller than
mountain i suppose. With all that said, gravity is
actually pretty much unexplained really.
2.) if you look at the source code you should understand that by increasing the frequency you increase the number of iterations and if your CPU was slow to begin with it explains all the problems.. ergo, on the contrary - use LARGEST POSSIBLE fixed step (10Hz, 30Hz, 60Hz.. )
3.) You do not need to "scale" anything, all you need is to ENLARGE your OBJECTS, so that minimum sized shape is 0.2meters in size. Mass and everything else should stay the SAME as in real rife, INCLUDING GRAVITY. - use METERS as distance units, smallest shape SHOULD be 0.2 METERS
[MISSING-REPEAT]
Oct 7, 2008
>>"I
don't think your post addresses my questions."
- tp,
just try it, try to read it once again,
try to understand it.. try to practically experiment and
then make conclusion
>>"I
don't wish to turn this thread into another physics
theory lesson"
-what do you mean?
you came here with incomplete understanding asking for
help, actually asking for lesson, right? so im giving you
theoretical lesson and practical examples, why do you
mind?
>>"so
I'd like to limit this to a couple of brief replies and
then get back to the simulation problems."
- that is exactly what i gave you, is it not?
let me point at it more directly..
>>"When you scale things up, you're not simply affecting object sizes"
-that is your 1st mistake right there, as i explained already:
* R --> You do not
need to "scale" anything, all you need is to
ENLARGE your OBJECTS, so that minimum sized shape is
0.2meters in size. Mass and everything else should stay
the SAME as in real rife, INCLUDING GRAVITY.
* R --> NASA -"The weight, size, and shape of the
object are not a factor in describing a free fall(no air
resistance)"
>>"It's
obvious you haven't tried to do this yourself, as the
effect is quite easily noticeable."
- no,
it is obvious that you have not tried what i suggest
i, of course, have tried it all,
otherwise i would not find appropriate to be giving any
advice ..as a matter of fact, im kind of a supreme expert
on these matters - but, sure, i'll leave you be if you
wish
>>"My CPU isn't slow, and that's not relevant here."
- that is your 2nd
mistake right there
it is relevant, sure it is!
..who is asking a question here? why do you argue instead
of to try and understand, or try in practice what i told
you?
>>"I
was saying the simulation loses real time applicability
when I need to run it at 6000 Hz to obtain
stability."
- of course you are having problems.. and i
already explained why:
* R --> if you look at the source code you should
understand that by increasing the frequency you increase
the number of iterations and if your CPU was slow to
begin with it explains all the problems.. ergo, on the
contrary - use LARGEST POSSIBLE fixed step (10Hz, 30Hz,
60Hz.. )
>>"The
whole topic is about a simulation where the objects are
small, such as pieces on a chess board where the largest
shape is about 0.05 meters."
- yes,
and thats why i told you this:
R --> You do not need to "scale" anything,
all you need is to ENLARGE your OBJECTS, so that minimum
sized shape is 0.2meters in size. Mass and everything
else should stay the SAME as in real rife, INCLUDING
GRAVITY.
use METERS as distance units, smallest shape SHOULD be
0.2 METERS
but of course,
if you prefer to continue and have the same problems
still, you are free to ignore all this yet again
cheerio
*** messages DELETED, banned ..y'$#%@!! ***
-"Sic patiuntur omnes qui increduli sunt et
quicumque ignorant diaboli astutias,
spem suam ponentes in eum; et operibus eius se
obligantes,
simul merguntur cum illo in gehennam ignis ardentis: ita
astutia eius."
Seraphim and Nephilim, the chronicles
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