Issue 51

K. Li et alii, Frattura ed Integrità Strutturale, 51 (2020) 386-397; DOI: 10.3221/IGF-ESIS.51.28 389 In the {O A -X A Y A Z A } coordinate system, the three-dimensional coordinates of S (x a , x b , x c ) are expressed as follows:      = = = vt z y x a a a     sin cos (1) The distance from the sensor to the surface of the object can be expressed by Equation (2):   tan d = (2) Therefore, the position coordinates of any light spot S can be expressed as:        = = = vt z d y d x a a a     tan sin tan cos (3) Then the laser scanned image is obtained and establish the coordinate system {O-XYZ} is established, as shown in Fig. 3. Figure 3 : Laser scanning image coordinate system {O-XYZ}. The laser scanned image is an object model that is recombined by laser spots. Therefore, the detection data of the structure can be acquired by the position change information of any two points P 1 (x 1 , y 1 , z 1 ) and P 2 (x 2 , y 2 , z 2 ) on the image. The deformation information of the structure can be calculated by the formula (4). 2 1 2 2 1 2 12 ) ( ) ( y y x x PP − + − = (4) where y = vt, x is related to the variables α, θ and the size of the detected object. The variation of the structure elevation information can be obtained by formula (5). 1 2 z z D − = (5) where  tan d z = . Therefore, the established 3D laser scanning system can detect structural damage by acquiring the positional changes of the spots on the laser scanned image.