A method for generating a trimming setpoint for an ophthalmic lens to be fitted in a surround of a spectacle frame, includes: a) within a coordinate system of the surround identified by a horizontal axis, acquiring the shape of a longitudinal profile of the surround and the perimeter length of this longitudinal profile; b) within an optical coordinate system of the ophthalmic lens which is identified by a centering point and by a horizontal axis and which is made to coincide with the coordinate system of the surround, centering and orienting the longitudinal profile, c) projecting the acquired longitudinal profile onto a curved surface deduced from a curvature parameter of the ophthalmic lens or from the spectacle frame, d) correcting in two operations, the shape of the projected longitudinal profile, so as to equalize its perimeter length with the perimeter length of the acquired longitudinal profile, and e) deducing from the corrected longitudinal profile the trimming setpoint.