Projected velocity field for some toy models with angle i, j (the kinematic axis is shown as a dashed line, the projected major axis is a solid line). Panel a: projection onto the plane of the sky of an observer with (i = 45 ° ,j = 0°) of disk with purely circular motion. Panel b: as in panel a but for a disk with purely radial velocities. Panel c: as in panel a but for an ellipse with purely circular motions. Panel d: as in panel c but for i = 45 ° ,j = 30°. Panel e: as in panel c but for i = 45 ° ,j = 60°. Panel f: as in panel c but for an ellipse with purely radial motions. Panel g: as in panel f but for i = 45 ° ,j = 30°. Panel h: as in panel f but for i = 45 ° ,j = 60°.