Sketch of the coordinate system adopted to calculate the visibility of ECM emission from the active field lines. The top left vectors show the relation between the line of sight and rotation coordinates, and the top right vectors show the relation between the rotation and magnetic vectors. The bottom panel shows the vectors that define the plane containing active field line, which emits in a hollow cone configuration centred on the vector ĉ, which has an opening angle α. The visibility of the ECM emission is dependent on the angle γ formed between ĉ and the line of sight $\widehat{x}$ (see Equation 1).