MANHOLE IRON LID MAXIMUM STEP DIFFERENCE AMOUNT MEASURING APPARATUS AND METHOD, PIXEL RESOLUTION CALCULATING APPARATUS USED THEREFOR, MANHOLE IRON LID MAXIMUM STEP DIFFERENCE PLACE DETECTING APPARATUS, PIXEL RESOLUTION CALCULATING METHOD, AND MANHOLE IRON LID MAXIMUM STEP DIFFERENCE PLACE DETECTING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a technique for measuring a maximum step difference amount of a manhole iron lid from a manhole receiving frame efficiently with high precision from a digital image obtained by photographing a manhole.SOLUTION: A manhole iron lid maximum step difference amount measuring method includes: detecting lateral and longitudinal both-end parts of a manhole receiving frame by subjecting a digital image to a texture mapping process and edge filtering process; calculating an absolute length per pixel on the basis of lateral and longitudinal pixel values of the manhole receiving frame in the digital image and actual size values of the manhole receiving frame; detecting a step candidate from shade parts in the digital image by subjecting the digital image to an edge filtering process; determining a shade part having longest lateral continuity among the shade parts as a step of the manhole iron lid and then calculating longitudinal pixel values of a part where the longitudinal width of the shade part is longest; and measuring the absolute amount of a maximum step amount of the manhole iron lid from the manhole receiving frame on the basis of the longitudinal pixel values of the shade part and the absolute length per pixel.