Displacement/distortion measuring method and displacement/distortion measuring apparatus

A structural displacement/strain measuring apparatus comprising:

• a hand-held line scanner apparatus that is manually re-positionable relative to a surface of a to-be-measured object, wherein the hand-held line scanner apparatus includes a light source and a line sensor;
• and
• means for
• measuring a predetermined time before and after a time elapse,
• capturing images of the surface of the to-be-measured object by
• arranging the line scanner apparatus in close adhesion or in vicinity of the surface of the to-be-measured object, and
• calculating a displacement or strain of the to-be-measured object by
• adapting an image analysis method to the images of the surface of the to-be-measured object captured before and after the time elapse, wherein the image analysis includes
• determining a first minute area in the image before the time elapse,
• acquiring a distribution of gradation values in the first minute area,
• comparing a distribution of gradation values in the image after the time elapse and the distribution of gradation values in the first minute area, and
• specifying, in the image after the time elapse, a second minute area of which a correlation with the distribution of gradation values in the first minute area is maximized, wherein the hand-held line scanner apparatus is connected to the means.