Nervous system

**Petr Schreiber** · 24-09-2007, 15:48

Hi,

I tried to create symmetrical shape and put it "on head" by default.

What happens ?

At least on my PC it starts to rotate counter clock wise.
Maybe it is somehow related to forgotten mysterious prophecy about random ODE mood ( seek any medieval book for the reference

).

Does the same occur on your PC too, or system stays at same position forever ?

Thanks,
Petr

**Michael Hartlef** · 24-09-2007, 15:53

Hi Petr,

what are you doing with ODE? Where is the new TBGL ;D Just kiddin'

I'll check it tonight. I remember something odd and similar when I was trying to code an entity system
for the IBP 3D Pack. On my system (Intel) I got a strange behavior and and on Athlons everythign was fine.
Something math related. What is your CPU?

**Petr Schreiber** · 24-09-2007, 16:03

Hi Mike,

Where is the new TBGL ;D

Good try to make me heartattack

I am working on it, I am working on it ( even started to write docs

)

To make situation even more funny, I have AMD Sempron 64bit. So not Intel

I presume it could be related to fact ODE uses SINGLEs ( at least classic ODE from offical website ).
Maybe some rounding errors?. How hard is to store integer numbers in SINGLE variable ???

Thanks,
Petr

**ErosOlmi** · 24-09-2007, 16:10

Petr,

for sources so big, better to add as attach file otherwise forum color syntax parser will take a lot of web server CPU. Thanks

I tested and it start in perfect balance but after 2 secs start going down on the left (un-clock) and an infinite pendulus left/right starts. At every left/right it seems loosing a little bit. So it is not a 360 round but a 359.9999, 359.9998, 359.9997, ...

Are you using SINGLE (sorry no time right now to go though source code)? SINGLEs have low precision and if used in math expressions rounding problems are quite sure.

Eros

**Petr Schreiber** · 24-09-2007, 16:36

Hi Eros,

I am sorry, but I like colors

I removed the code section and attached whole script.

I am also quite curious why ODE uses SINGLEs by default, I think unprecision is not worth savings in memory ( DOUBLEs are twice as big ), especially in software dedicated to simulations

Thanks,
Petr

**ErosOlmi** · 24-09-2007, 16:41

Petr,

thanks a lot. For scripts around 100 lines, seems no problem, but for more than 300 lines it seems our server is suffering a bit :-[

I tried to change all SINGLE to DOUBLE but again same behave. I've not review all the code but just: find(SINGLE) - replace(DOUBLE) rough method.
On my machine it takes about 2/3 secs before to start moving. Maybe we can calculate how many main loops it takes to move and if all the same in all machines, it is quite sure a rounding problem. I will study the script more this night when back from work.

Ciao
Eros

**Petr Schreiber** · 24-09-2007, 16:43

When you add following code to the script ( after objects are created and jointed, but before loop ):

type t_xyzpos
x as dReal
y as dReal
z as dReal
end type

dim pos1 as t_xyzpos at dBodyGetPosition ( mySphereBody(%SPH_LOWESTRIGHT2) )
dim pos2 as t_xyzpos at dBodyGetPosition ( mySphereBody(%SPH_LOWESTLEFT2) )

msgbox 0, STR$(pos1.x)+STR$(pos1.y)+STR$(pos1.z)
msgbox 0, STR$(pos2.x)+STR$(pos2.y)+STR$(pos2.z)

... you will see values are stored without any round off errors !
It is weird. It must be something in ODE.

ODE is compiled already to work with SINGLEs, so re-declarataion sadly cannot help.
If somebody knowing C could recompile ODE.DLL with DOUBLE precision option it would be interesting to see if it makes difference.

I tried even constant simulation step, and it did the same fall.
Interesting is that setting too big step makes ODE crazy and it totally destroys the construction

Thanks,
Petr

**Michael Hartlef** · 24-09-2007, 18:25

Everything works like a charm here. ThinBasic 20070909

By working like I charm I mean, that it stays on top for about 2 seconds and then starts falling down and then swing left/right.

**kryton9** · 24-09-2007, 18:39

First, thanks for the demo... neat to see so much happening, toon shading, shadows, physics, cool mouse interaction with scene!!!

It stays still for a few seconds and does come down on the left side. Would such a structure be in balance in reality? It seems to act as you would think, at least the way I would think, and it falling to the left is correct with the Earth's rotations effects

Put a ball on the table and if it moves, with no outside forces, then worry

**Petr Schreiber** · 24-09-2007, 18:50

Hi guys,

thanks for the tests.
Did you know clicking using middle mouse button / mouse wheel click allows you to push objects like with finger

?

Kent has good point about earth rotation, but as ODE allows to setup gravity, I think it also does not presume Earth conditions for all operations. But good idea!

I am fool I do not backup my work, because I did similar object, like a grid, which was symmetrical and I think it rotated clockwise.

I need to do more tests

Thanks,
Petr