Hi JP, Thanks. Sorry for the noise on the list. I remember the convention now that you mention it. However, I was implementing a rigid body simulation using the OSG quaternion, and doing the multiplications in the order described in the paper I was using as a reference. Mysteriously, I was adding energy to the system, and finally tracked it down to this. ;) I think I've learned my lesson... Again, sorry for the noise. Matt
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of J.P. Delport Sent: Sunday, September 14, 2008 5:06 AM To: OpenSceneGraph Users Subject: Re: [osg-users] Quaternion Multiply Hi, the matrix pre vs postmultiply (row and column major) issue comes up every now and again on the list, so also see the mailing list archives: http://news.gmane.org/gmane.comp.graphics.openscenegraph.user Basically, OSG follows a (consistent) matrix multiplication order convention that seems to differ from what most people expect first time around. The quaternion multiplication order was made so that the order is consistent with the matrix mult order used by OSG. The best way to sort this out for yourself is to write a rotation problem out on paper and then implement the same thing as a matrix and quaternion operation in OSG. See the code in osgunittests for the quaternion tests. There is also code in OSG to print out the values of matrices and quaternions that can help. regards jp Matt Sutton wrote: > Hi Folks, > > I know I must be missing something, but can someone help me out with > this. It is true that multiplying two quaternions, a and b, can be seen > as a linear transform of one on the other, right? So, for quaternions > a, b and c you can have something like: > > > > c = a*b > > > > Option 1: Using a linear transform on b constructed from a > > c = A*b > > Option 2: Using a linear transform on a constructed from b > > c = B*a > > > > Note that matrices A and B have a slightly different construction since > the product of two quaternions is not commutative. > > > > But, it looks to me like the OSG implementation is effectively using > option 1, but constructing the "A" matrix from the b quaternion? So, it > looks like a*b is actually b*a. Is that intended? If I'm totally > seeing this wrong, please forgive me. I've attached a test file. > > > > Thanks, > > Matt Sutton > > www.padtinc.com > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or g -- This message is subject to the CSIR's copyright terms and conditions, e-mail legal notice, and implemented Open Document Format (ODF) standard. The full disclaimer details can be found at http://www.csir.co.za/disclaimer.html. This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. MailScanner thanks Transtec Computers for their support. _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or g _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
