Rotating objects attached to other objects

Question

I have a question concerning a single mesh (building) that contains a collection of animated objects (these objects make up the complete building, rising up from the ground when

Answer 1

The transformation you're looking for is this:

Matrix positionRotationMatrix = Matrix.CreateTranslation(-parentPosition) 
                               * Matrix.CreateFromQuaternion(parentRotation) 
                               * Matrix.CreateTranslation(parentPosition);
Vector3 translation = Vector3.Transform(parentPosition + relativePosition,
                               positionRotationMatrix);

You define your world matrix with the new sub-objects position (translation variable):

Matrix worldMatrix = Matrix.CreateScale(scale)
                * Matrix.CreateFromQuaternion(rotation)
                * Matrix.CreateFromQuaternion(parentRotation)
                * Matrix.CreateTranslation(translation);

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To demonstrate, here's a cube (parent) that is being rotated around it's position, with an arrow whose position and rotation are defined in relation to its parents position and rotation. The arrow follows the cubes rotation, and rotates around it's Z axis independently.

Values used for the demonstration:

parentPosition = Vector3(-1.1f, 0f, -2); //cube
relativePosition = Vector3(0, 0, -3); //arrow
parentRotation = Quaternion.CreateFromRotationMatrix(
                       Matrix.CreateRotationZ(angle) 
                     * Matrix.CreateRotationY(angle) 
                     * Matrix.CreateRotationX(0.5f));
rotation = Quaternion.CreateFromYawPitchRoll(0f, 0f, angle);
angle += 0.05f;