Two-Dimensional and Three-Dimensional CNN-Based Simultaneous Detection and Activity Classification of Construction Workers

The type and duration of construction workers' activities are useful information for project management purposes. Therefore, several studies have used surveillance cameras and computer vision to automate the time-consuming process of manually gathering this information. However, the three-stage method they have adopted consisting of separate detection, tracking, and activity classification modules is not fully optimized. Additionally, the activity classification module is trained per-clip/segment on trimmed video clips and fails when applied to long untrimmed construction videos. This paper aims to (1) investigate the benefits of a fully optimized method such as you only watch once (YOWO) and a per-frame and per-worker annotated untrimmed data set over the previous approach for activity recognition of construction workers; (2) propose an improved version of YOWO, called YOWO53, to improve detection performance; (3) propose a semiautomatic data set annotation; (4) conduct a sensitivity analysis to compare the performance of YOWO, YOWO53, and the three-stage method; and (5) conduct a case study to compute the percentage of different workers' activities. YOWO53 improves the detection recall of YOWO by up to 3%, and the classification accuracy of the three-stage method by 16.3%. Although YOWO53 has a lower inference speed, it is still sufficiently fast for productivity analysis.

Automated summary

This paper investigates the advantages of a fully optimized method and an annotated untrimmed data set for activity recognition of construction workers. It proposes an improved version of YOWO to enhance detection performance and conducts a sensitivity analysis and a case study to compare different methods.