WIKI Update Request RE: [ODE] Jitters and GeomTransforms
hplus-ode at mindcontrol.org
Mon Feb 7 09:29:50 MST 2005
> However, the documentation seems a little light on the issue of how
> ODE creates their 4x3 rotation matricies. Does anyone know if it is in
> column order, or row order? I typically just use 3x3 (Leaving out
> entires, 3, 7 and 11) rotation matricies, and I think it's that
> section of code that was wrong.
Not only is there a question of column or row major, but there's also
a question of pre-multiply vs post-multiply convention.
The ODE Wiki actually has documentation on the ODE matrix layout, and
gives functions for converting between ODE and DirectX matrices.
You can also run the following experiment:
dQFromAxisAndAngle( q, 0, 1, 0, 3.1416/2 );
dRfromQ( R, q );
This shows that the matrix after rotating around Y for quarter turn is:
0-3 0 0 1 
4-7 0 1 0 
8-11 -1 0 0 
Remember that this should take X to -Z, so the lower-left -1 must be
multiplied by "X" from an input vector, so input vectors
This assumes row major storage, and post-multiplied column vectors. If
you believe your layout is column major, then it assumes pre-multiplied
row vectors. This means that the un-used fourth elements could contain
a translation, if you wanted to use them for that.
I can't seem to actually edit the Wiki, so please stick this into the
FAQ section, something about matrix lay-out.
More information about the ODE