A pretty good explanation of row vector and transform Matrix here. http://msdn.microsoft.com/en-us/library/windows/desktop/bb206269(v=vs.85).aspx
On Tue, Aug 27, 2013 at 1:39 PM, Grahame Fuller <grahame.ful...@autodesk.com > wrote: > I'm pretty sure it's the row versus column vector issue. In a nutshell, > most of the CG world, including Softimage, treats vectors as rows, i.e., > 1x3 matrices. The rest of the world, including most references you'll find > for math, physics, robotics, etc., treats vectors as columns, i.e., 3x1 > matrices. > > In a row-vector world, you construct your transform by inserting your > X,Y,Z basis vectors into a matrix as rows. The order of multiplication for > transforms is Mchild x Mparent, and when multiplying a vector and matrix > the vector goes on the left and the matrix on the right. > > In a column-vector world, it's the opposite. You construct your transform > by inserting your X,Y,Z basis vectors into a matrix as columns. The order > of multiplication for transforms is Mparent x Mchild, and when multiplying > a vector and matrix the vector goes on the right and the matrix on the left. > > In particular, note that the row-vector transform is transposed (mirrored > across the diagonal) from the column-vector transform. So if the formulas > for your individual rotation matrices matX, matY, and matZ came from a > reference that uses column-vectors, you need to transpose the matrices. > > To calculate the various rotation orders, you just need to multiply the > matrices in different orders. In a row-vector world, you use reverse order, > for example, if you want XYZ order then you calculate matZ x matY x matX. > Luckily matrix multiplication is the same in both row-vector and > column-vector worlds, so you can save some processor time by figuring it > out long-hand and stuffing the final values into the full transform matrix > directly, like in the code sample you showed, but of course it's easy to > make a typo or other mistake. > > gray > > From: softimage-boun...@listproc.autodesk.com [mailto: > softimage-boun...@listproc.autodesk.com] On Behalf Of Eric Thivierge > Sent: Monday, August 26, 2013 8:21 PM > To: softimage@listproc.autodesk.com > Subject: Re: SI Matrix3 and Maths > > Thanks Raf I saw that today. It's a problem somewhere with my matrix > multiplication I think. Tried a bunch of different combos but I'm thinking > it's what Matt touched on either the row / column mixing or a mistake in > the shorthand somewhere. > > -------------------------------------------- > Eric Thivierge > http://www.ethivierge.com > > On Mon, Aug 26, 2013 at 8:15 PM, Raffaele Fragapane < > raffsxsil...@googlemail.com<mailto:raffsxsil...@googlemail.com>> wrote: > The rotation order matters. > It's as simple as each rotation pushing a gimbal along by a linear > distance of trigonometric functions of that angle in turns, in the rotation > order... order. > Wikipedia has the matricial forms: > http://en.wikipedia.org/wiki/Rotation_matrix#Basic_rotations > What's not working from that? Or if you haven't looked at it, shame on you! > > >
