Evaluation of Acquisition Strategies for Image-Based Construction Site Monitoring

Abstract

Commission V WG 4 KEY WORDS: photogrammetric point cloud, construction site monitoring, 3D building model, BIM ABSTRACT:Construction site monitoring is an essential task for keeping track of the ongoing construction work and providing up-to-date information for a Building Information Model (BIM). The BIM contains the as-planned states (geometry, schedule, costs, ...) of a construction project. For updating, the as-built state has to be acquired repeatedly and compared to the as-planned state. In the approach presented here, a 3D representation of the as-built state is calculated from photogrammetric images using multi-view stereo reconstruction. On construction sites one has to cope with several difficulties like security aspects, limited accessibility, occlusions or construction activity. Different acquisition strategies and techniques, namely (i) terrestrial acquisition with a hand-held camera, (ii) aerial acquisition using a Unmanned Aerial Vehicle (UAV) and (iii) acquisition using a fixed stereo camera pair at the boom of the crane, are tested on three test sites. They are assessed considering the special needs for the monitoring tasks and limitations on construction sites. The three scenarios are evaluated based on the ability of automation, the required effort for acquisition, the necessary equipment and its maintaining, disturbance of the construction works, and on the accuracy and completeness of the resulting point clouds. Based on the experiences during the test cases the following conclusions can be drawn: Terrestrial acquisition has the lowest requirements on the device setup but lacks on automation and coverage. The crane camera shows the lowest flexibility but the highest grade of automation. The UAV approach can provide the best coverage by combining nadir and oblique views, but can be limited by obstacles and security aspects. The accuracy of the point clouds is evaluated based on plane fitting of selected building parts. The RMS errors of the fitted parts range from 1 to a few cm for the UAV and the hand-held scenario. First results show that the crane camera approach has the potential to reach the same accuracy level.

Practical Implementation of Photogrammetry for the Modelling of a Cylindrical Historical Building

“…The baseline, distance between each station, is determined in order to have a good overlap between successive photos (around 80%). This overlap should allow to see every points in at least three images (Tuttas et al, 2016). The capture distance from the * Corresponding author wall is chosen so that the researched ground pixel size could be achieved, which is linked to the desired level of details:…”

Multi-Building Extraction and Alignment for As-Built Point Clouds: A Case Study With Crane Cameras

“…But UAVs have certain disadvantages. Aside from the need for flight permissions (Cardot, 2017), there are restrictions such as a security distance to be maintained from buildings and cranes, and maximal flight heights, which can pose a problem for tall buildings (Tuttas et al, 2016). Also, UAVs can only operate in the active area of construction when the cranes do not move, such as during breaks.…”

“…We review the exceptions subsequently. Tuttas et al (2016) were the first to study as-built point clouds generated from crane cameras. They did a comparative analysis of image acquisition from crane cameras with hand-held cameras and UAVs.…”

“…However, georeferencing asbuilt data based on site referencing systems is a common practice in the industry (Wang and Kim, 2019) and is thus considered necessary for this work. Crane camera technology offers some key advantages over its counterparts like Light Detection And Ranging (LiDAR) and Unmanned Aerial Vehicles (UAVs), such as being fully automated, low-cost, and low-labor (Tuttas et al, 2016). The 3D point clouds obtained from crane cameras can allow daily and automatic inference of the current floor under construction, while 2D images can be used to infer the state of cast-in-place concrete roof slabs.…”