Correction for geometrical center-to-limb systematics in maps of circulation velocity v^ac for LCT and TD using HMI observations. This example shows the correction of v^ac maps at 60° latitude. a) Patch 1 (raw data) is located at 60° latitude at the central meridian. Patch 2 (systematics data) is situated at the equator, 60° west of the central meridian. We corrected the raw data by subtracting patch 2 from patch 1 (after rotating patch 2 anticlockwise by 90°). We note that we also use measurements of the systematics from the east for the correction (rotated clockwise by 90°). This is omitted in the sketch for clarity. b) Maps of v^ac for LCT and f-mode TD. The three columns of panels show (from left to right) the measured raw data at 60° latitude, the measured systematics from 60° west and east (rotated and averaged), and the corrected data.