A navigation assistance device, said device being designed to be placed on a carrier and comprising: - at least one inertial unit; - an integration module designed to estimate the position, speed and orientation of said carrier on the basis of data supplied by said inertial unit; - a digital map of the locations in which said carrier is present, said map being designed to store a navigable network, over which said carrier can move; characterised in that said device further comprises: - a module for generating position pseudo-measurements on the basis of the position estimated by said integration module and of cartographic data supplied by said digital map, a position pseudo-measurement indicating the position that must be estimated by said integration module in the event of movement constraints imposed by said digital map of the locations, said module for generating position pseudo-measurements being designed to project the position computed by said integration module on said navigable network so as to generate said position pseudo-measurement; - an indirect extended Kalman filter connected by a switch to said module for generating position pseudo-measurements, said filter being designed to estimate any errors relating to the position, speed and orientation estimated by said integration module on the basis of the position pseudo-measurements generated by said module for generating position pseudo-measurements; - a module designed to indicate the availability of a pseudo-measurement of said module for generating position pseudo-measurements and designed to control the closure of said switch when a pseudo-measurement is available and designed to otherwise open said switch; the output of said integration module, which indicates the position, speed and orientation estimate, being connected to said module for generating position pseudo-measurements, to said Kalman filter and to the positive input of a filter of a subtractor, the errors estimated by said Kalman filter being fed to the negative input of said subtractor, the output of said subtractor supplying the corrected position, speed and orientation of the carrier. - at least one inertial unit; - an integration module designed to estimate the position, speed and orientation of said carrier on the basis of data supplied by said inertial unit; - a digital map of the locations in which said carrier is present, said map being designed to store a navigable network, over which said carrier can move; - a module for generating position pseudo-measurements on the basis of the position estimated by said integration module and of cartographic data supplied by said digital map, a position pseudo-measurement indicating the position that must be estimated by said integration module in the event of movement constraints imposed by said digital map of the locations, said module for generating position pseudo-measurements being designed to project the position computed by said integration module on said navigable network so as to generate said position pseudo-measurement; - an indirect extended Kalman filter connected by a switch to said module for generating position pseudo-measurements, said filter being designed to estimate any errors relating to the position, speed and orientation estimated by said integration module on the basis of the position pseudo-measurements generated by said module for generating position pseudo-measurements; - a module designed to indicate the availability of a pseudo-measurement of said module for generating position pseudo-measurements and designed to control the closure of said switch when a pseudo-measurement is available and designed to otherwise open said switch;