Parametric tolerance determining methods for steel rail height and rail bottom concavity

The invention discloses parametric tolerance determining methods for steel rail height and rail bottom concavity, and solves the problem of large error in a conventional determining method. The parametric tolerance determining method for the steel rail bottom concavity comprises the steps of firstly, performing fitting calculation of an equation of a rail bottom straight line, dividing the scanned cross section contour rail bottom of the steel rail into three parts, finding out the maximum distance from each part to the rail bottom straight line and coordinates of corresponding points, and determining an equation of a rail bottom reference line by comparing the three distances; and secondly, selecting the maximum value as the rail bottom concavity by comparing the distances from the points of the rail bottom to the rail bottom reference line, and finally performing parametric tolerance determination. The parametric determining method for the steel rail height comprises the steps of respectively calculating the distances from points on the rail head to the rail bottom reference line, taking the maximum value as the steel rail height, and then performing parametric tolerance determination. The invention is high in measuring precision, the rail height and the rail bottom concavity can be accurately measured and determined even if the rail bottom is uneven, and the methods can be achieved through a computer program.