[ODE] vector has zero size

[Bram Stolk]

Wouter Mollemans wrote:
> TIMESTEP: 0.001 (but even with 0.0001, i have this problem)
> ERP : 0.01

Sounds like a very low ERP to me.
Such a value would mean that only a very small fraction of the
error is corrected.

  Bram

> CFM : 0.07
> OBJECTS: trimeshes (approx 4000 triangles)
> 
> Greetings
> Wouter
> 
> Hampus Soderstrom wrote:
>> Hi Wouter,
>>
>> I meant you should try different ERP and CFM values, not making them 
>> smaller.
>>
>> What timestep are you running? Lowering that can help too.
>>
>> Are you using any ball joints or angular motors, thoose can be unstable 
>> aswell if you have a wide range in their stops.
>>
>> /Hampa
>>
>> On 18 Oct 2006, at 10:12 PM, Wouter Mollemans wrote:
>>
>>> I don't think the problem arises from performing simulations with 
>>> small ERP or CFM values. To clarify:
>>> after i call the nearcallback function and perfrom dCollide(), the 
>>> position of most contact points is completely correct. Only for a few 
>>> (most often only for one point) a NaN position value is returned. So I 
>>> don't think that simulation goes wrong.
>>>
>>> Best regards
>>> Wouter
>>>
>>> Hampus Soderstrom wrote:
>>>> Hi,
>>>> I think the best way to get rid of this is to fine tune ERP and CFM 
>>>> values.
>>>> If it is a case of exploding simulation that causes this, adding 
>>>> damping and making sure the mass of objects isn't to small can also 
>>>> help.
>>>> /Hampa
>>>> On 18 Oct 2006, at 8:20 PM, Wouter Mollemans wrote:
>>>>> Thx I will try to use your solution, but this is of course only a work
>>>>> around.  Does anyone has an idea what causes these infinite values?
>>>>>
>>>>> Is it the collision detection algorithm? I noticed that the collision
>>>>> algorithm (dCollide()) frequently reports a NaN value for the position
>>>>> value of the first contact (contact[0]).
>>>>>
>>>>>
>>>>> Alex Green wrote:
>>>>>> Apporx once every 12000 simulations I get the same error. The error 
>>>>>> can
>>>>>> be detected. I run a function called 'checkPhysicsForError()' per 
>>>>>> frame.
>>>>>> It works as follows:
>>>>>>
>>>>>> bool checkPhysicsForError(void){
>>>>>> dReal *pos = (dReal*) dBodyGetPosition(bodyID of one of my boxes);
>>>>>> if(!(pos[0]==pos[0]) || !(_finite(pos[0])))
>>>>>> {
>>>>>>     dWorldDestroy(world);
>>>>>>     reset all my stuff
>>>>>>     create everything again;
>>>>>>     rewind one test (ie do the one that failed from the beginning);
>>>>>>     return true;
>>>>>> }
>>>>>> else return false;
>>>>>> }
>>>>>>
>>>>>> Notes:
>>>>>> pos[0] == pos[0] checks for NAN (not a number);
>>>>>> _finite() is windows, is there a cross platform check?
>>>>>>
>>>>>> Cheers -alex
>>>>>>
>>>>>> Wouter Mollemans wrote:
>>>>>>> After some debugging, I noted that some of the collision points are
>>>>>>> lying at infinity. This causes dNormalize4() to go nuts. Has anyone
>>>>>>> seen this problem before and do you know what causes this effect?
>>>>>>>
>>>>>>> Greetz
>>>>>>> Wouter
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> In my simulator I try to fit two rigid objects into eachother (a
>>>>>>>> little bit like a 3D puzzle).  The rigid objects are trimeshes
>>>>>>>> (around 4000 triangles) and all my joint are of the type contact.
>>>>>>>> Sometimes this works nicely, but mostly I get following message: 
>>>>>>>> "ODE
>>>>>>>> message 2 : vector has zero size" emmtted by dNormalize4().
>>>>>>>> Consequently the velocity becomes Nan and my simulation is ruined.
>>>>>>>>
>>>>>>>> Is there a solution? Is there a maximum number of triangles that can
>>>>>>>> be used or what is the source of the error?
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> Greetz
>>>>>>>> Wouter
>>>>>>>>
>>>>>>>>
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>>
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-- 
Bram Stolk, VR Engineer SARA, Amsterdam.   tel +31 20 592 3000

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