A REC can have any orientation in space. It is limited by a cylindrical elliptical surface and by two plane faces perpendicular to its axis. (If the cylinder axis is parallel to one of the coordinate axes, it is worth considering instead the use of an infinite cylinder XEC, YEC or ZEC (see below), leading to increased tracking speed). Each REC is defined by 12 numbers: V_x, V_y, V_z (coordinates of the centre of one of the elliptical plane faces), H_x, H_y, H_z (x, y and z components of a vector corresponding to cylinder height, pointing to other plane face), R1_x, R1_y, R1_z (components of a vector corresponding to the minor half-axis of the cylinder elliptical base), R2_x, R2_y, R2_z (ditto for the major half-axis). A REC definition extends over 2 lines in default fixed format, or over 4 lines in high-accuracy body fixed format. Example in default fixed format:*...+....1....+....2....+....3....+....4....+....5....+....6....+....7..REC 1 -10.0 12.0 7.0 0.0 58.0 0.0 9. 0.0 0.0 0.0 0.0 17.0* (an elliptical cylinder 58 cm long parallel to the y axis, with minor* half-axis 9 cm long parallel to the x coordinate axis, major* half-axis 17 cm long parallel to the z axis, base centred at point* x=-10, y=12, z=7)The same example in high-accuracy body fixed format:*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+.REC 1 -10.0 12.0 7.0 0.0 58.0 0.0 9. 0.0 0.0 0.0 0.0 17.0 The same, in free format: REC pipesurf -10.0 12.0 7.0 0.0 58.0 0.0 9.0 0.0 0.0 0.0 0.0 17.0