Can somebody explain what happens here??

Question

Hi everyone.
I was just wondering if someone could explain the following piece of code to me.
Thanks a lot.
Transform3D t3d = new Transform3D();
Transform3D ct3d = new Transform3D();
Matrix4d matrix = new Matrix4d();
t3d.rotY(angle);
viewingPlatformTG.getTransform(ct3d);
ct3d.get(matrix);
ct3d.setTranslation(new Vector3d(0.0, 0.0, 0.0));
ct3d.mul(t3d);
ct3d.setTranslation(new Vector3d(matrix.m03, matrix.m13, matrix.m23));
viewingPlatformTG.setTransform(ct3d);
////////////////////////////////////////////////////

Answer 1

Well I think the following task shall be accomplished:
1)The rotation around the y axis should be concatenated to the rotation already done with the object.
2)The rotation center shall be the center of the object (here the Viewingplatform), i.e. the center of the local coordinate system.
For 2) first the translation part is saved in matrix (in fact the whole transformation is saved), then the translation part is set to 0,0,0 which leaves only the rotation part (thus the center of local coordinate system is center of global coordinate system). Then the new rotation is concatenated. Then the translation part (contained in matrix.m03, ...) is restored thus the object is at the original position again.
Hope that helps.