A workflow for producing point clouds used in transport infrastructure retrofit construction

In this technical note, we propose a workflow that engineers will implement when creating a point cloud survey for transportation infrastructure retrofit projects. The workflow is based on a critical review of two case studies of bridge retrofit where critical phases in the design are identified and related to the outputs of point cloud surveys as well as the BIM design process. The review was carried out form a sub-contractor point of view and includes the expert opinions of professionals involved in the case studies as means of validation of the findings. From the case studies, we identified key workflow activities in a typical construction project cycle while mapping areas for improvement of the efficiency when producing a point cloud. We identified that working with large file sizes of the point cloud survey not only hinders productivity in terms of time needed for download and analysis, but also in terms of need for intervention from an engineer who would align the new design elements with the existing structure in situ. The absence of common referencing system and the presence of alien objects during the survey were also identified as hindrances to the accuracy and productivity of the point cloud. The critical review and the expert opinion provided information to support the development of a best practice approach that is applicable to point cloud production, which is a common approach to survey existing infrastructure undergoing retrofit construction. The main results, or benefits, from this approach include increased productivity due to the size of the point cloud files and due to quality assurance and planning prior to undertaking the point cloud survey. Point cloud file size can be reduced up to 90% to suit the resolution optimal to the project, and this can bring up to 97% reduction in time needed for file download. This workflow could be used as a best practice guidance in addition to the relevant national standards and act as an example framework that experts in the industry should produce for other BIM assignments.