Matrix order

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Larry Ramey (ramey++at++ccpo.odu.edu)
Fri, 17 Sep 1999 13:12:47 -0400


The standard order of transformations for a hierarchical scene involves
postmultiplying the transformation matrix for a child by the matrix for
the
parent. For instance, assume your scene involves a hand attached to an
arm attached to a body. To get a transformation matrix H for the hand,
postmultiply the arm's transformation matrix (A) by the body's (B): H =
AB. To transform the hand object (at location h in hand coordinates) to
body coordinates, calculate h' = hH.

OK, This SOUNDS nice, but anyone who knows matrix math KNOWS you can't
multiply

0
1 * 4x4 Matrix
0
1

Now you CAN do

              0
              1
4x4 Matrix * 0
              1

I am assumeing that this wierdness might have something to do with the
fact that performer matrices print out their translation elemnets in the
4th row instead of the 4th column like a NORMAL GL matrix.

Can someone PLEASE explain in what freaking order the DCS(SCS,FCS) in a
scene graph are multiplied in!!!! I would greatly appreceate it if the
word Postmuliply wasn't used at all. Please, Please, Please use normal
MATH notation. (4x4)*(column vector) = (transformed vector)

If am not an idiot, but something about performer math is really
odd........

Please if you can CC a copy to my address as I only get info performer
in digest mode.

Thank you in advance.

---------------------------------------------------------------
Larry E. Ramey ramey++at++ccpo.odu.edu
757-683-3439 (CAVE) 757-683-5335 (VEL Lab)
"I eat weirder things than you in my cereal" - Zaphod Bebblebrox
"Maybe life is like a ride on a freeway/
dodgeing bullets while your trying to find your way" - Offspring


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