A post processing navigation mapping system including: a camera subsystem; a GNSS/INS subsystem; one or more processors (30, 40, 60) that receive measurement data and image data from the subsystems, the one or more processors being configured to calculate sets of position, velocity and attitude solutions and associated variances that correspond in time to images taken by the camera subsystem, by processing the measurement data received from the GNSS/INS subsystem in a time domain filter forward in time and backward in time, thereby obtaining forward and backward solutions respectively, determine which of the sets of solutions are reliable based on a comparison of their respective forward and backward solutions and associated variances and using the reliable sets of solutions to determine position, velocity and attitude information for a camera included in the camera subsystem, and for sets of solutions determined to be unreliable further process the GNSS/INS measurement data and the corresponding image data from images that correspond in time to determine further processed solutions and using the further processed solutions to determine position, velocity and attitude information for one or both of the camera and an INS measurement unit included in the GNSS/INS subsystem. a camera subsystem; a GNSS/INS subsystem; one or more processors (30, 40, 60) that receive measurement data and image data from the subsystems, the one or more processors being configured to calculate sets of position, velocity and attitude solutions and associated variances that correspond in time to images taken by the camera subsystem, by processing the measurement data received from the GNSS/INS subsystem in a time domain filter forward in time and backward in time, thereby obtaining forward and backward solutions respectively, determine which of the sets of solutions are reliable based on a comparison of their respective forward and backward solutions and associated variances and using the reliable sets of solutions to determine position, velocity and attitude information for a camera included in the camera subsystem, and for sets of solutions determined to be unreliable further process the GNSS/INS measurement data and the corresponding image data from images that correspond in time to determine further processed solutions and using the further processed solutions to determine position, velocity and attitude information for one or both of the camera and an INS measurement unit included in the GNSS/INS subsystem. calculate sets of position, velocity and attitude solutions and associated variances that correspond in time to images taken by the camera subsystem, by processing the measurement data received from the GNSS/INS subsystem in a time domain filter forward in time and backward in time, thereby obtaining forward and backward solutions respectively, determine which of the sets of solutions are reliable based on a comparison of their respective forward and backward solutions and associated variances and using the reliable sets of solutions to determine position, velocity and attitude information for a camera included in the camera subsystem, and for sets of solutions determined to be unreliable further process the GNSS/INS measurement data and the corresponding image data from images that correspond in time to determine further processed solutions and using the further processed solutions to determine position, velocity and attitude information for one or both of the camera and an INS measurement unit included in the GNSS/INS subsystem.