Three-dimensional reconstruction of the extended filament. (a) Schematic illustration of triangulation and a filament (red) above the solar surface. Points A and B show schematic locations of the SDO and STEREO-A spacecraft, respectively. C is the highest point of the filament. Point P shows the orthogonal projection of C onto the sphere. Points M and N are the projections of point C on the sphere along the LOS of SDO (AC) and STEREO-A (BC). (b) Selected points M (blue) in the AIA 304 Å image along the filament axis are used for the 3D reconstructions. (c) STEREO-A image showing the points N (blue) matching the same features observed in the SDO image.