Modeling of architectural and engineering structures allows making comparisons between the expected or desired state of a building through a digital model, based on the main purpose of modeling. In this way, it becomes possible to plan for the operations performed or intended to be performed on the structure.
The sequential workflow of scanning an object and modeling point clouds with a 3D Laser Scanner measurement focuses mostly on building modeling. Because, many architectural renovation and restoration processes are carried out on the current state of buildings. Many examples in this area, scanning both historical and modern buildings, continue to increase day by day. In addition, BIM (Building Information Modeling), which is a very important work area of the last period, has started a new era in terms of processing building models and using the information obtained from the model.
The fact that building models have become a GIS (Geographic Information Systems) project has attracted the architecture, engineering and construction sectors. Building models subjected to BIM have started to be evaluated with their different features and a new process has been formed with the information content expected from the model. BIM has become an operating, monitoring and quality control tool that offers the opportunity to use from building constructions to very large engineering structures and also provides benefits proportional to the size of the structure.
In particular, building models are often produced to analyze multi-storey and large structures. It is obligatory to check at certain stages of production whether a building facade is of the quality specified, for example, it is straight along an axis, in its project, or not. Many building elements controlled by traditional measuring techniques are products that give more efficient results with their produced models and contribute to the construction process in terms of both cost and quality assurance (QA).
Due to the aforementioned importance of BIM, many researchers are working on building BIM techniques and increasing their usability for large projects. At this point, it is envisaged to create a robotic system that can navigate inside a building, make 3D measurements, and then automatically produce a highly accurate, semantically rich building model. In the robotics industry, many researchers are investigating the problem of mapping indoor facilities. (Huber vd., 2010)
Figure 1: An example of modeling errors detected by the deviation analysis method for QA. The upper floor’s wall is offset about 3 cm from the wall of the lower floor, but it is modeled using two walls in the same plane.The difference between the point cloud and the model is shown in blue and green when they are below 3 cm and 0.5 cm, respectively. (Huber vd., 2010)
Figure 2: Example point cloud of a tunnel. (Slob & Hack, 2004)
Project-based special measuring setups can be prepared for measuring these types of structures. In order to measure bridge and viaduct piers, custom bent-up bars and pillars are installed in certain places in a position suitable for 3D laser scanning measurement, and the manufacturing progress of these structures are followed continuously with models produced with point cloud. In order to carry out the measurement of highways and tunnels, a rail mechanism is prepared and MLT (Mobile Laser Scanning) measurements are also made.
Laser scanners are frequently used to measure tunnel geometry. These types of structures can be measured faster with Terrestrial Laser Scanners (YLT) with higher detail and accuracy. For example, the thickness of the applied shotcrete can be monitored in this way and final geometry controls of the tunnel can be performed with this method. Since the internal geometry can be captured with very high precision, these models may also be suitable for monitoring the deformation. (Slob & Hack, 2004)
In addition, special building projects are modeled as high visual reality for promotional purposes. There is no difference between the produced model and the final product, it is only used for promotion and prestige.
Figure 3: A very detailed building model obtained from point cloud.