public Transform combineWithParent(Transform parent) {
        //applying parent scale to local scale
        scale.multLocal(parent.scale);
        //applying parent rotation to local rotation.
        parent.rot.mult(rot, rot);
        //applying parent scale to local translation.
        translation.multLocal(parent.scale);
        //applying parent rotation to local translation, then applying parent translation to local translation.
        //Note that parent.rot.multLocal(translation) doesn't modify "parent.rot" but "translation"
        parent.rot
                .multLocal(translation)
                .addLocal(parent.translation);

        return this;
    }
Combines with the argument and returns the (modified) current instance.
This method is used to combine Node and Spatial transforms.

@param parent the parent transform (not null, {@code parent.rot.norm()}
    approximately equal to 1, unaffected unless it's <code>this</code>)
@return the (modified) current instance (for chaining)
jme3-core/src/main/java/com/jme3/math/Transform.java