Sensor-Based Calibration of Camera’s Extrinsic Parameters for Stereophotogrammetry

Stereophotogrammetry is a well-recognized technique for structural health monitoring. Before performing any quantitative stereophotogrammetry measurement, the cameras must be calibrated to obtain the intrinsic and extrinsic parameters of the stereovision system. However, when large-sized structures are to be monitored, the calibration process is challenging and limits the use of stereophotogrammetry. In this article, a sensor-based calibration method for determining the extrinsic parameters of a stereovision system is presented and validated. A multisensor board has been developed that synchronizes inertial measurement units (IMUs) and a laser on a single board computer to measure the spatial orientation and the distance of two paired cameras and compute the extrinsic parameters of the stereovision system. The effectiveness of the sensor-based calibration is evaluated through both analytical studies to quantify the effects of performance degradation caused by the sensors’ noise as well as laboratory tests. Results show that the sensor-based calibration is effective in quantifying displacement with errors below 3% when compared to measurements performed using a stereovision system calibrated with the traditional image-based procedure.