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Hi, I read in my 3D math book that “heading-pitch-bank” was also called “roll-pitch-yaw” with roll=bank and yaw=heading, but it is not very clear if the order of rotations (around y, x and z axes for heading-pitch-bank) was the same or not (z-x-y axes for roll-pitch-yaw? or same as heading-pitch-bank, heading/bank and roll/yaw words are just swapped?). Thank you.

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RPY is the same as the heading notation. Its also called XYZ Euler, which means you apply the rotation matrices like so:
Rr = RotationMatrix of ROLL degrees about X axis
Rp = RotationMatrix of PITCH degrees abotu Y axis
Ry = RotationMatrix of YAW degrees about Z axis
Assumign orientation matrix O

New O = Ry*Rp*Rr*O, the roll is applied first I believe.

Ok, thanks.

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it depends on how you're multiplying the component matrices, premultiplication of HPB will be equivalent to postmultiplication of RPY (BPH).

also, roll is not necessarily about the x axis, some animation packages (lightwave for example) define roll as the z axis and pitch as the x axis. Sort of analogous to being in an airplane with the X axis running along the wings.

whatever you're doing, make sure you settle on a scheme, and do whatever conversions you need to make other stuff the -same- as your stuff, if you try and mix pre/post multiplication or axis orders you will end up with all sorts of insanely hard to debug problems, and generally long after you thought your matrix classes were bulletproof

james

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