Centroids of the radio emission at 173 MHz. The top panel shows the centroids of the radio emission from the perspective of STEREO-B (left) and Earth (right). The centroids are plotted over running difference images from EUVI at 195 Å and COR1 on board STEREO-B and AIA at 211 Å from SDO. The bottom panel shows the centroids together with the 3D reconstruction of the shock from three perspectives: STEREO-B (left), solar north pole (middle), and Earth (right).