Method, carried out by a computer or set of computers, for generating correction information, hereinafter referred to as "tropospheric correction information", wherein the tropospheric correction information comprises information for correcting observations useful for estimating at least one of phase ambiguities and a position of at least one global or regional navigation satellite system receiver, hereinafter abbreviated as NSS receiver, the at least one NSS receiver being within the troposphere and on or above a region of interest of the Earth's surface, the method comprising: for each of a plurality of reference stations in the region of interest, receiving raw observations, hereinafter referred to as "multiple-frequency-signals-based raw observations", obtained by the reference station observing NSS multiple-frequency signals from a plurality of NSS satellites over multiple epochs; obtaining information, hereinafter referred to as "precise satellite information", on: the orbit position of each one of the plurality of NSS satellites, and a clock offset of each one of the plurality of NSS satellites, or information derived from the precise satellite information; for each of the plurality of reference stations, estimating at least one troposphere correction parameter by evaluating NSS observation equations using the precise satellite information or the information derived from the precise satellite information, and the received multiple-frequency-signals-based raw observations or a linear combination thereof; generating the tropospheric correction information, based on the estimated at least one troposphere correction parameter per reference station, wherein the tropospheric correction information comprises at least one mathematical function, each of which being hereinafter referred to as "regional tropospheric delay function", in the sense that the tropospheric correction information provides at least one indication, each indication referring to a particular function among a plurality of possible functions, and its coefficients, hereinafter referred to as "regional tropospheric delay coefficients", the at least one regional tropospheric delay function and its regional tropospheric delay coefficients representing a delay, hereinafter referred to as "tropospheric delay", affecting a NSS signal passing through the troposphere in the region of interest; and sending the generated tropospheric correction information. for each of a plurality of reference stations in the region of interest, receiving raw observations, hereinafter referred to as "multiple-frequency-signals-based raw observations", obtained by the reference station observing NSS multiple-frequency signals from a plurality of NSS satellites over multiple epochs; obtaining information, hereinafter referred to as "precise satellite information", on: the orbit position of each one of the plurality of NSS satellites, and a clock offset of each one of the plurality of NSS satellites, or information derived from the precise satellite information; the orbit position of each one of the plurality of NSS satellites, and a clock offset of each one of the plurality of NSS satellites, or information derived from the precise satellite information; for each of the plurality of reference stations, estimating at least one troposphere correction parameter by evaluating NSS observation equations using the precise satellite information or the information derived from the precise satellite information, and the received multiple-frequency-signals-based raw observations or a linear combination thereof; the precise satellite information or the information derived from the precise satellite information, and the received multiple-frequency-signals-based raw observations or a linear combination thereof; generating the tropospheric correction information, based on the estimated at least one troposphere correction parameter per reference station, wherein the tropospheric correction information comprises at least one mathematical function, each of which being hereinafter referred to as "regional tropospheric delay function", in the sense that the tropospheric correction information provides at least one indication, each indication referring to a particular function among a plurality of possible functions, and its coefficients, hereinafter referred to as "regional tropospheric delay coefficients", at least one mathematical function, each of which being hereinafter referred to as "regional tropospheric delay function", in the sense that the tropospheric correction information provides at least one indication, each indication referring to a particular function among a plurality of possible functions, and its coefficients, hereinafter referred to as "regional tropospheric delay coefficients", the at least one regional tropospheric delay function and its regional tropospheric delay coefficients representing a delay, hereinafter referred to as "tropospheric delay", affecting a NSS signal passing through the troposphere in the region of interest; and sending the generated tropospheric correction information.