Representation of shock-wave triangulation using three different viewpoints, with the 23 Jul. 2012 event. Top: three points of view running difference images of a halo CME in white-light, with STEREO-A, SoHO/LASCO, and STEREO-B (shown from left to right). Red dashed lines show the shape of a reconstructed shock wave. Bottom: view of the ecliptic from the solar north that shows the spacecraft position around the Sun at the CME eruption time. The direction of propagation of the CME is shown by the black arrow. This panel is produced using Solar-MACH online toolprotect (https://solar-mach.streamlitapp.com/).