Analytical Approach to Augmenting Site Photos with 3D Graphics of Underground Infrastructure in Construction Engineering Applications

This paper proposes an analytical approach to incorporating computer-generated three-dimensional (3D) graphics of invisible underground infrastructure into site photos so as to present a richer and more integral view of the site situation in construction engineering applications. The proposed approach simulates the image-forming process of a camera and produces a virtual photo of the underground scene, whose virtual coordinate axes coincide with the real coordinate axes of the aboveground site scene. As a result, the virtual photo and the site photo can be seamlessly merged in terms of perspective, position, and scale. This research simplifies the calculation of the camera’s spatial orientation by use of only two reference points’ positions, i.e., the camera station position and the object focus position. The whole procedure of the proposed approach is analytical and can be automated into a computer program. In practice, nondestructive subsurface imaging technologies are generally used to obtain the spatial data of the underground infrastructure, which can be readily processed into a 3D as-built model as one component in composing the virtual underground scene. The proposed approach is demonstrated with a case study in which the underground as-built data are superimposed onto the aboveground site photo for the purpose of quality investigation of a bored pile construction.