Hi,
I come across an interesting problem. And though i have already resolved
it, i want to know _why_ this problem occured.
I tried to rotate a vector. Since there is no such a function in Java3D
i composed it myself. In theory everything should be quite simple:
Vector*rotationMatrix3D = rotatedVector. I took rotation matrix from
Transform3D object (some rotation was already there). But the vector was
rotated _clockwise_, though such functions as rotX or rotY produce
counter
clockwise rotation as well as rotation matrices of Transform3D itself.
When i inverted rotation matrix prior to multiplying vector by it,
everything worked fine and vector was rotated _counter clockwise_.
I wonder why such a thing occurred? In books dedicated to 3D it's _not_
said that rotation matrix should be inverted. Moreover, simple
calculations on the paper say the same: no invertion should be made
prior to multiplying it by vector. In a book it is said that rotation
around Y axis could be made by means of the following rotation matrix:
---
cos(a) 0 -sin(a)
0 1 0
sin(a) 0 cos(a)
---
If we multiply (0, 0, 1) vector by this matrix, the new coords of the
vector would be
( sin(a), 0, cos(a) ), that is rotaion was made counter clockwise.
Do the rotation matrices look the same in Java3D? Can somebody explain
all that stuff about inverting matrices, please? Where is the trick?
Thanks a ton,
vladimir
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