Hyoseong Lee

Measurement of 3-D Vibrational Motion by Dynamic Photogrammetry Using Least-Square Image Matching for Sub-Pixel Targeting to Improve Accuracy.

This paper deals with an improved methodology to measure three-dimensional dynamic displacements of a structure by digital close-range photogrammetry. A series of stereo images of a vibrating structure installed with targets are taken at specified intervals by using two daily-use cameras. A new methodology is proposed to accurately trace the spatial displacement of each target in three-dimensional space. This method combines the correlation and the least-square image matching so that the sub-pixel targeting can be obtained to increase the measurement accuracy. Collinearity and space resection theory are used to determine the interior and exterior orientation parameters. To verify the proposed method, experiments have been performed to measure displacements of a cantilevered beam excited by an electrodynamic shaker, which is vibrating in a complex configuration with mixed bending and torsional motions simultaneously with multiple frequencies. The results by the present method showed good agreement with the measurement by two laser displacement sensors. The proposed methodology only requires inexpensive daily-use cameras, and can remotely detect the dynamic displacement of a structure vibrating in a complex three-dimensional defection shape up to sub-pixel accuracy. It has abundant potential applications to various fields, e.g., remote vibration monitoring of an inaccessible or dangerous facility.

Deformation Measurement of a Railroad Bridge Using a Photogrammetric Board without Control Point Survey

We propose a photogrammetric board to measure the deformation of a railroad bridge using close-range photogrammetry. The method can be used to compute the exterior orientation parameters and determine three-dimensional (3D) coordinates from images without measuring the control points. The bridge deformation measured using the proposed method was compared to that measured with a 3D laser tracker. The measurement error was within 1 mm, and the proposed method can measure the deformation of an I-plate girder of a railroad bridge. This method may be an alternative to precise stability inspections and bridge inspections.

Measurement of 3-D vibration by dynamic photogrammetry using least-square image matching for sub-pixel targeting

This paper deals with a methodology to measure 3-D dynamic displacements of a structure by the digital close-range photogrammetry. Using stereo sequence images of a vibrating structure taken by two cameras, a method is proposed to accurately trace the spatial displacement of the structure in 3-dimensional space. This method combines the correlation and the least square image matching so that the sub-pixel targeting is achieved to increase the measurement accuracy. Experiments have been successfully performed to measure displacements of a beam under forced vibration in both bending and torsional modes simultaneously with multiple frequencies. The proposed method only requires inexpensive daily-use cameras, and can remotely detect the dynamic full-field displacement of a structure vibrating in a complex 3-D defection shape up to the sub-pixel accuracy. It has various potential applications, e.g., remote vibration monitoring of a non-accessible or dangerous facilities, etc.