Re: [Plib-users] Matrix rotation question

[Curtis L. O. <cu...@me...>]

It sounds like you may be experiencing "gimble lock".  If so, you
should take a look at the definitive document on the subject:

    http://web2.airmail.net/sjbaker1/eulers_are_evil.html

Regards,

Curt.


McEvoy, Nick writes:
> Sorry matrix operations are not my strong point ... can somebody please
> point out my stupid mistake !?
> 
> I'm developing a space sim with PLIB ... and I have a problem where my
> spaceship behaves in a crazy manner when its heading is directly 'UP' and
> tries to roll to the left or right.
> 
> // Say my initial my position is as follows: (ie. I'm pointing directly up
> ... NOTE: this only happens when pointing directory UP !!!)
> sgCoord mPosition;
> sgSetCoord(&mPosition, 0.0f, 0.0f, 0.0f, 0.0f, 90.0f, 0.0f);
> 
> // Say my direction change is as follows: (ie. I'm rolling to the left)
> sgVec3 mDirChange;
> sgSetVec3(mDirChange, 0.0f, 0.0f, -0.01f);
> 
> // I have a loop where the direction change is applied as follows to update
> the hpr:
> sgMat4 POS, ROT;
> sgMakeCoordMat4(POS, &mPosition);
> sgMakeRotMat4(ROT, mDirChange);
> sgPreMultMat4(POS, ROT);
> sgSetCoord(&mPosition, POS);
> 
> // Why does this loop toggle the hpr part of my mPosition as follows:
> (causing the model to FREAK OUT flipping between ~0 and 90)
> hpr:	0, 90, 0
> hpr:	0, 90, 90.01
> hpr:	0, 90, 6.18986e-006
> hpr:	0, 90, 90.01
> hpr:	0, 90, 1.38196e-005
> hpr:	0, 90, 90.01
> hpr:	0, 90, 1.38196e-005
> etc ...
> 
> Any help appreciated,
> Nick
> mailto:nic...@as...
> http://members.ozemail.com.au/~ndmcevoy/
> 
> 
> _______________________________________________
> plib-users mailing list
> pli...@li...
> http://lists.sourceforge.net/lists/listinfo/plib-users

-- 
Curtis Olson   Human Factors Research Lab       FlightGear Project
Twin Cities    cu...@hf...                cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org