1. A method for generating an optimum measurement subset from a set of weighted input global navigation satellite system (GNSS) measurements, wherein the number of weighted input GNSS measurements in the set of weighted input GNSS measurements is a first integer, wherein the number of weighted input GNSS measurements in the optimum measurement subset is a specified second integer, and wherein the specified second integer is less than the first integer, the method comprising: performing the steps of: receiving the set of weighted input GNSS measurements; generating a group of trial measurement subsets by removing a different individual weighted input GNSS measurement from the set of weighted input GNSS measurements; for each trial measurement subset in the group of trial measurement subsets, calculating a value of accuracy criterion for at least one target parameter; determining a minimum value of accuracy criterion based on the values of accuracy criterion calculated for each trial measurement subset in the group of trial measurement subsets; and assigning the trial measurement subset having the minimum value of accuracy criterion as a current selected trial measurement subset; and iteratively performing the steps of: determining whether the number of weighted input GNSS measurements in the current selected trial measurement subset is equal to the specified second integer; upon determining that the number of weighted input GNSS measurements in the current selected trial measurement subset is equal to the specified second integer: assigning the current selected trial measurement subset as the optimum measurement subset; and upon determining that the number of weighted input GNSS measurements in the current selected trial measurement subset is not equal to the specified second integer: generating a new group of trial measurement subsets from the current selected trial measurement subset by removing a different individual weighted GNSS measurement from the current selected trial measurement subset; for each trial measurement subset in the new group of trial measurement subsets, calculating the value of accuracy criterion for the at least one target parameter; determining a new minimum value of accuracy criterion based on the values of accuracy criterion calculated for each trial measurement subset in the new group of trial measurement subsets; and assigning the trial measurement subset with the new minimum value of accuracy criterion as the current selected trial measurement subset; wherein the set of weighted input GNSS measurements corresponds to a first time instant, and wherein the optimum measurement subset is a first optimum measurement subset, further comprising: receiving a set of updated weighted input GNSS measurements corresponding to a second time instant; generating an updated first optimum measurement subset by updating values of the weighted input GNSS measurements in the first optimum measurement subset; determining whether the number of updated weighted input GNSS measurements in the updated first optimum measurement subset is less than the specified second integer; and upon determining that the number of updated weighted input GNSS measurements in the updated first optimum measurement subset is less than the specified second integer: performing the steps of: generating a group of trial updated measurement subsets from the updated first optimum measurement subset by adding a different individual updated weighted GNSS measurement to the updated first optimum measurement subset; for each trial updated measurement subset in the group of trial updated measurement subsets, calculating the value of accuracy criterion for the at least one target parameter; and determining a minimum value of accuracy criterion based on the values of accuracy criterion calculated for each trial updated measurement subset in the group of trial updated measurement subsets; and assigning the trial updated measurement subset with the minimum value of accuracy criterion as a current selected trial updated measurement subset; and iteratively performing the steps of: determining whether the number of updated weighted input GNSS measurements in the current selected trial updated measurement subset is equal to the specified second integer; upon determining that the number of updated weighted input GNSS measurements in the current selected trial updated measurement subset is equal to the specified second integer: assigning the current selected trial updated measurement subset as a second optimum measurement subset; and upon determining that the number of updated weighted input GNSS measurements in the current selected trial updated measurement subset is not equal to the specified second integer: generating a new group of updated trial measurement subsets from the current selected updated trial measurement subset by adding a different individual updated weighted GNSS measurement to the current selected trial updated measurement subset; for each trial updated measurement subset in the new group of trial updated measurement subsets, calculating the value of accuracy criterion for the at least one target parameter; determining a new minimum value of accuracy criterion based on the values of accuracy criterion calculated for each trial updated measurement subset in the new group of trial updated measurement subsets; and assigning the trial updated measurement subset with the new minimum value of accuracy criterion as the current selected trial updated measurement subset.