Non-contact type urban rail vehicle wheel set size on-line detection method

The invention discloses a non-contact type urban rail vehicle wheel set size on-line detection method. The method includes the following steps: successively arranging a first laser displacement sensorand a second laser displacement sensor on the inner side of a track in a train forwarding direction and successively arranging a fourth laser displacement sensor and a third laser displacement sensoron the outer side of the track, the first and fourth laser displacement sensors being symmetrical about the track and the second laser displacement sensor and the third laser displacement sensor being symmetrical about the track; carrying out coordinate rotation and transverse plane and feature point extraction on two-dimensional data points collected by the laser displacement sensors, and obtaining distances between the laser displacement sensors and a tread side of a vehicle wheel when the circle center of the vehicle wheel is in the central lines of the first and second laser displacementsensors and is in the centr