Elander, Daniel
Piai, Maurizio
Roughley, John
Article History
Received: 17 April 2020
Revised: 29 May 2020
Accepted: 8 June 2020
First Online: 29 June 2020
Change Date: 17 December 2020
Change Type: Erratum
Change Details: Equation (3.24) contains a typo, the right-hand-side needs to be divided by 4. Figures 4 and 5 have been improved, and the cutoff artefacts are not visible any more. The caption of figure 5 has been amended accordingly.