This is an erratum for the following article:
F. Devernay et O. Faugeras, Straight Lines Have to Be Straight:
Automatic Calibration and Removal of Distortion from Scenes of Structured Environments, *Machine Vision and Applications*, 1,
2001, pp. 14-24 (PDF).

Formula (9) should read (in maple code):

rd := (R+sqrt(Delta))**(1/3)-Q/((R+sqrt(Delta))**(1/3)):

and not

rd := (R+sqrt(Delta))**(1/3)+Q/((R+sqrt(Delta))**(1/3)):