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deshan
12-05-2013, 02:27 AM
Hi all,

I am trying to extract the forward vector from 4x4 transformation matrix.
I have two forms of calculation one is for nodes in the scene graph and other is for camera.

This is how I calculate transformation matrix for node.




// Matrix44 is a float[16]

Matrix44 nodeTranslationMat; // translation matrix for node

Matrix44 nodeRotationMat; // rotation matrix for node

Matrix44 transformationMatrix= nodeTranslationMat* nodeRotationMat; // transformation matrix



And this is how I do it for camera



Matrix44 cameraTranslateMat; // translation matrix for camera

Matrix44 cameraRotationMat; // rotation matrix for camera

Matrix44 transformationMatrix= cameraRotationMat* cameraTranslateMat; // transformation matrix, note - multiplication order is different form node


And then for the camera forward vector I can extract using above transformation matrix like


Vector3f forwardVector = Vector3f(transformationMatrix[2], transformationMatrix[6], transformationMatrix[10]);

But If I do this above to find the forward vector for node it's not works.

Could you please help me to find it it?

CarstenT
12-05-2013, 01:50 PM
Changing the order of rotation and translation makes for two different transformations .. reasonably with two different z-vectors in the output transformation-matrix.

deshan
12-11-2013, 01:53 AM
Thanks for the reply.

After doing visual experiments, I realized that the forward vector for node can be calculate as

Math::Vector3f(transformationMatrix[8], transformationMatrix[9], transformationMatrix[10]);

For camera, forward vector is

Math::Vector3f(transformationMatrix[2], transformationMatrix[6], transformationMatrix[10])

So if the multiplication order is different


Matrix44 nodeTransformationMatrix= nodeTranslationMat* nodeRotationMat;
Matrix44 cameraTransformationMatrix= cameraRotationMat * cameraTranslationMat;

forward vector calculation should also different?

Sorry I am trying to learn the basics.

CarstenT
12-11-2013, 07:52 AM
deshan,
have you checked the visual differences between the two transformations?
If you do two nodes, one with each transformation .. you'll see why you may not be able to match up the two 'forward' vectors.
A 'forward' vector is not an inherent quality of a matrix .. it may fit the z-vector for the camera, but did you make your node in coordinates, where the z-vector is 'forward'?