[Rock-dev] Representation of invalid positions vs. unknown uncertainty

[Janosch Machowinski]

Uhm, why don't we just set the position
vector to nan in case it is unknown and
the covariance matrix to nan in
case it is unknown ?
Greetings
     Janosch

On 19.01.2012 19:32, Leif Christensen wrote:
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> Hi,
>
> some thoughts on that:
>
> With respect to IEEE 754 floating point conventions, using NaN for
> unknown uncertainty is an option, since it is commonly used for
> undefined, but also uninitialized or even unknown values. Con is, that
> operations with NaN may throw an error if honoring singalling NaNs is
> on (-fsignaling-nans). On most system the default will be quiet NaNs,
> that will propagate through your operations.
>
> Concerning 0 vs. Inf in the off-diagonal positions, there should be no
> difference at least for the case multiplying with a vector:
>
> case 1:
> Inf 0   0	a 	aInf  + b0   + c0
> 0   Inf 0   x   b  =    a0    + bInf + c0
> 0   0   Inf	c       a0    + b0   + cInf
>
> 	Inf
> =	Inf
> 	Inf
>
> case 2:
> Inf Inf Inf   a		aInf  + bInf   + cInf
> Inf Inf Inf x b = 	aInf  + bInf   + cInf
> Inf Inf Inf   c		aInf  + bInf   + cInf
>
> 	Inf
> =	Inf
> 	Inf
>
> since Inf + Inf is defined as Inf.
>
> If a or b or c is zero, the resulting row will be NaN for both cases.
>
> Greetings,
> Leif
>
> P.S. Hm, just checked 0 multiplied by Inf which gives on my system
> - -NaN and not NaN, using gcc -std=gnu99. Weird
>
>
>
> On 19.01.2012 16:18, Sylvain Joyeux wrote:
>> On 01/19/2012 09:48 AM, Jakob Schwendner wrote:
>>>> Which is the default value set by RigidBodyState::invalidate()
>>>> and marks the position as unknown (infinite uncertainty on the
>>>> position).
>>> I would also think that the NaNs in the off-diagonal are
>>> misplaced if it wants to say infinite uncertainty. Should be 0 in
>>> my opinion.
>> That's something I meant to ask ...
>>
>> What would
>>
>> Inf 0   0 0   Inf 0 0   0   Inf
>>
>> actually mean (if it does mean something). What would be the
>> difference with:
>>
>> Inf Inf Inf Inf Inf Inf Inf Inf Inf
>>
>> Sylvain _______________________________________________ Rock-dev
>> mailing list Rock-dev at dfki.de
>> http://www.dfki.de/mailman/cgi-bin/listinfo/rock-dev
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-- 
  Dipl. Inf. Janosch Machowinski
  SAR-&  Sicherheitsrobotik

  DFKI Bremen
  Robotics Innovation Center
  Robert-Hooke-Straße 5
  28359 Bremen, Germany

  Phone: +49 (0)421 178 45-6614
  Fax:   +49 (0)421 178 45-4150
  E-Mail: robotik at dfki.de

  Weitere Informationen: http://www.dfki.de/robotik
  -----------------------------------------------------------------------
  Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
  Firmensitz: Trippstadter Straße 122, D-67663 Kaiserslautern
  Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
  (Vorsitzender) Dr. Walter Olthoff
  Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
  Amtsgericht Kaiserslautern, HRB 2313
  Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
  USt-Id.Nr.:    DE 148646973
  Steuernummer:  19/673/0060/3
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