Method implemented by computer means, for determining a position of an optical lens member having a surface placed on a lens blocking ring, the blocking ring comprising a bearing zone arranged to bear at least partially the placed surface of the optical lens member when said optical lens member is placed on the lens blocking ring, the method comprising: - a reference system providing step during which a reference system is provided, the reference system comprises a main axis perpendicular to a main plane (X,Y) defined by two axes perpendicular to each other and to the main axis, - a blocking ring data providing step during which blocking ring data representing, in the reference system, a plurality of at least three points of the bearing zone, is provided; - an optical lens member surface data providing step, during which optical lens member surface data is provided, the optical lens member surface data representing, in the reference system, the placed surface of the optical lens member to be placed on the blocking ring, - a position parameters providing step during which position parameters are provided, the position parameters (TX, TY, RZ) defining a position of a reference point of the placed surface with respect to the main plane of the reference system and an orientation, about the main axis of said placed surface at said reference point, - an initial position determining step during which the position of the placed surface of the optical lens member is determined according to the position parameters, characterized in that the method further comprises: - a repositioning step during which the placed surface is virtually translated along the main axis and rotated about the two perpendicular axes (X;Y), from said initial position, to be set in a virtual position, - an altitude determination step during which a difference in position along the main axis between each of the points of the blocking ring data and the placed surface of the optical lens member in said virtual position is determined, wherein the repositioning and altitude determining steps (S6, S7) are repeated so as to minimizing the difference in position along the main axis between the points of the blocking ring data and the placed surface of the optical lens member and by imposing that for each point of the blocking ring data, the distance in position along the main axis with the placed surface of the optical lens member is greater than or equal to zero for determining complementary position parameters (RX, RY, TZ) of the optical lens member. - a reference system providing step during which a reference system is provided, the reference system comprises a main axis perpendicular to a main plane (X,Y) defined by two axes perpendicular to each other and to the main axis, - a blocking ring data providing step during which blocking ring data representing, in the reference system, a plurality of at least three points of the bearing zone, is provided; - an optical lens member surface data providing step, during which optical lens member surface data is provided, the optical lens member surface data representing, in the reference system, the placed surface of the optical lens member to be placed on the blocking ring, - a position parameters providing step during which position parameters are provided, the position parameters (TX, TY, RZ) defining a position of a reference point of the placed surface with respect to the main plane of the reference system and an orientation, about the main axis of said placed surface at said reference point, - an initial position determining step during which the position of the placed surface of the optical lens member is determined according to the position parameters, characterized in that the method further comprises: - a repositioning step during which the placed surface is virtually translated along the main axis and rotated about the two perpendicular axes (X;Y), from said initial position, to be set in a virtual position, - an altitude determination step during which a difference in position along the main axis between each of the points of the blocking ring data and the placed surface of the optical lens member in said virtual position is determined, wherein the repositioning and altitude determining steps (S6, S7) are repeated so as to minimizing the difference in position along the main axis between the points of the blocking ring data and the placed surface of the optical lens member and by imposing that for each point of the blocking ring data, the distance in position along the main axis with the placed surface of the optical lens member is greater than or equal to zero for determining complementary position parameters (RX, RY, TZ) of the optical lens member. - a repositioning step during which the placed surface is virtually translated along the main axis and rotated about the two perpendicular axes (X;Y), from said initial position, to be set in a virtual position, - an altitude determination step during which a difference in position along the main axis between each of the points of the blocking ring data and the placed surface of the optical lens member in said virtual position is determined,