Construction monitoring is one of the key applications of the 3D laser scanner. Starting with the inspection of the foundation excavations through to the weekly monitoring of the building shells, the laser scanner enables time and cost-efficient working. Any discrepancies between the building under construction and the existing plans are monitored. In this article we show how the laser scanner helps with construction monitoring and the advantages that are offered by the laser scanner compared with conventional measuring instruments.
Monitoring the progress of an office building using the 3D laser scanner
A job in the construction industry might involve monitoring the progress of an office complex. The excavation for the foundations has already been completed. The client requires weekly documentation and monitoring of construction progress for legal and technical documentation. The property is a modern design with lots of free-form surfaces. Conventional measuring instruments cannot measure it comprehensively. Laser scanners are predestined for this purpose. They are also suitable for documenting any discrepancies between the existing building and the planning documents. Laser scanning saves time and money. With the appropriate software it is also possible to produce new plans if necessary.
Surveying the property using a 3D laser scanner
First, the locations of the laser scanner are noted on a site plan. These are used as orientation points so that the results can later be pieced together on the PC. Laser scanners such as the FARO Focus3D record almost a million measuring points per second and produce a detailed, three-dimensional image of the status quo within a few minutes. In the second phase of the survey, the measured data must be evaluated. This is easily possible with a piece of software like SCENE.
The advantages of the 3D laser scanner in construction monitoring
One of the strengths of the laser scanner in construction monitoring is evident in the post-processing of the results. Once they have been entered into the PC, a point cloud is created from several million measuring points. From these survey data it is now possible to produce detailed plans, elevations and layouts. Any differences can be picked up in the variance comparison with the old plans.
1. Checking the foundation excavations
The laser scanner can be used to supervise the foundation excavations. It can be installed in the trench. In this way it is possible to measure any changes in the trench at regular intervals. Both the volume of excavated material and the size of the trench can be checked. The developer keeps control of costs, such as for the transportation of excavated material, as the laser scanner helps to optimize the use of lorry capacity. There is the further fact that conventional measuring instruments such as tacheometers only measure individual points. With 3D laser scanners it is now possible for the first time to record the entire excavation in a single measuring process. Any movements of the trench, such as slippage of the trench walls, are detected in good time.
2. Measuring free-form surfaces
The advantage of the 3D laser scanners over commonly used measuring instruments becomes even clearer when measuring free-form surfaces. These tacheometers and theodolites can only cope with a limited number of measuring tasks. They only measure individual coordinates of predefined objects. This means that it is not possible to measure free-form surfaces comprehensively. In contrast, the laser scanner records millions of measuring points in no time at all. They also remain archived and available to the architect long after the actual measurement. Individual values can be re-measured in the scan. When working with tacheometers you have to return to the building site for every new measurement.
3. Monitoring building progress
The 3D laser scanner displays its greatest strength in construction monitoring, when regularly recording the property. Here too the device can be installed, as when checking the excavation trench, and record the building shell. Previously it was necessary to engage a field survey firm to do the measurement. This can now be undertaken by architects themselves, saving time and money. With SCENE they can compare the 3D models produced from the survey results with the plans and detect any discrepancies. By regularly monitoring the progress of construction with the laser scanner, any problems can be promptly detected and prevented, so saving money.
This is just a brief outline of the possibilities that arise with a laser scanner in construction monitoring. 3D laser scanners record buildings faster and more comprehensively than has ever been possible with conventional methods. It is now also possible to survey free-form shapes comprehensively. Scans are compared with one another and with plans in order to detect any discrepancies and to document construction progress.