Assessing the Accuracy of Applying Photogrammetry to Take Geometric Measurements on Building Products

Abstract

The present research describes the fundamental working mechanism of photogrammetry and characterizes the errors of the photogrammetry-derived geometric measurements on building products in a systematic, practical, and statistically significant way. A site engineer simply takes snapshots of a building product with a digital camera from different angles. Back in office, the engineer derives as-built measurements through postprocessing those photos by use of photogrammetry software. The twelve objects sampled in our experiments were building products and building facilities found on the campus of Hong Kong Polytechnic University, yielding 79 paired geometric measurements (length, width, and height) by photogrammetry and by measurement tape, respectively. The biases and limitations of analyzing the agreement between two sets of measurements by regression and correlation coefficient techniques were first revealed. Then, the “95% limits of agreement” method was applied on the sample data and the confidence intervals were established for the limits of agreement derived, so as to ensure validity and statistical significance of the results. In short, the main contribution of this research lies in formalizing a statistically significant, quantitatively reliable technique to assess the accuracy of applying photogrammetry in particular applications of construction engineering. Through weighing the accuracy level achievable by photogrammetry against the accuracy level desirable in a particular application, the engineer makes the final decision on the applicability of the photogrammetry-based approach.