A method has steps of providing a three-dimensional (3-D) laser scanner, providing a computer, obtaining point group data (PGD) and calculating measuring an outline of a top reactant stratum from the PGD. The step of providing a 3-D laser scanner directs a 3-D laser scanner at reactant strata in a blast furnace and output PGD that represent digital data of an inside of the blast furnace. The step of providing a computer connects the 3-D laser scanner to a computer having a point group analysis program. The step of calculating an outline of the top reactant stratum from the PGD is performed by the point group analysis program to calculate an outline of the top reactant stratum in the blast furnace from the PGD. At least one two-dimensional laser scanner is used to measure a path of the reactant being charged.