Object plane deformation due to refraction in two-dimensional underwater motion analysis

The purpose of this study was twofold: (a) to investigate the effects of selected experimental factors on the magnitude of the object plane deformation due to refraction, and (b) to discuss their practical implications in an effort to improve the applicability of the 2-D DLT method in the underwater motion analysis. The RMS and maximum object plans reconstruction errors of various experimental conditions were computed systematically. To isolate the error due to refraction from the experimental errors, the comparator coordinates (image plane coordinates) of the control points were computed based on a theoretical refraction model rather than actual digitizing. It was concluded from a series of object plane reconstruction that among the distance and angle factors of the experimental setting in the 2-D underwater motion analysis, the camera-to-interface distance and the interface-to-control-object distance are the two major factors affecting the magnitude of the abject plane deformation. The other factors revealed only minor effects. The advantages of the 2-D DLT method over the traditional multiplier method in underwater motion analysis, such as oblique projection and multiple camera setup, were further discussed. Possible ways to reduce the maximum reconstruction error were also explored.