USE OF TERRESTRIAL LASER SCANNING TECHNIQUE IN ARCHITECTURAL RESTORATION PROJECTS: AN EXAMPLE PROJECT

A visit to field was performed upon the request for an architectural surveying and measurement of the hotel to be restored. We decided on the use of 3D Laser Scanning measurement technique following meetings with the customer and field surveys. However, given the existing conditions and circumstances, it was thought that laser scanning technique would not suffice alone, and therefore integrated measurement techniques were used. Accordingly, in addition to 3D Terrestrial Laser Scanner (TLS), for aerial photographs and facade images a drone (drone photogrammetry) was used and to generate point cloud in the desired coordinate system, total station devices were employed.

In order to enable complete and accurate architectural drawings to be made, detailed measurements were taken where every detail of the building could be seen. Laser measurements, particularly those intended for use in facade drawings and high structures, were performed by choosing a high resolution option from the settings. Integrity and accuracy of data was achieved and maintained through additional measurements of links and connections to enable conceiving and assessment of 3 separate buildings in different locations on one and the same plan and leveling of differences in elevations thereof.

Figure-1: An example point cloud image (Ground Control Points (GCPs) and laser scanning targets were used together for collecting drone photos.)

Processes of registration, filtering, coloring and coordinate transformation were performed respectively for point cloud. After final controls and checks on the deliverable point cloud, orthophotos thereof were generated for architectural drawings, and thereby the process was finalized.

Figure-2: Controlled point cloud image.

Orthophoto images were generated and prepared by taking into consideration such criteria as display of the level of detail, and suitability for creating drawings. In order to facilitate the work of architectural drawing team, images were prepared with their alternatives. Since point cloud data is also able to capture and save density data in addition to location information, it is possible to present the data in other forms of display as well. This is one of the strongest aspects of laser scanning measurement technique.

Figure-3: Orthophotography images of the same facade. (Above: RGB image, Below: A transparent image with marked outer contours)

All plans, sections or elevations for the architectural surveying project were prepared through drawings relying on the generated orthophotographs.

Figure-4: The most suitable form of display is selected for drawing from among various display options. (Walls, windows and doors as well as other on-site objects to be included in plan drawing)

Figure-5: Plan drawing over orthophotograph.

Figure-6: Orthophotography images of the same section. (Above: orthophotograph of RGB section, Below: Drawing over the orthophotograph)

Figure-6: Orthophotography images of the same facade elevation. (Above: RGB elevation orthophotograph, Below: Drawing over the orthophotograph)

Laser scanning technology does not advance solely through development of scanning units or manufacturing of scanning devices with more practical designs, but also software development efforts are underway to better understand and review the point cloud data. One of the FARO’s latest products, Scene2Go is an auxiliary and supportive application that allows opening, viewing and exploring of panoramic images of each center of scans, and even measuring therethrough.

Figure-7: In FARO Scene2Go app, scanning positions are displayed on real-world colored plans. Selection process is made easier by showing scans at different elevations with different colors.

Notably in applications such as these where there is no final deliverable data of point cloud, it is a highly useful and functional application for the architectural drawing team that will use the generated data. In this example project, panoramic images provided alongside the orthophoto images were used for control purposes so as to ensure that different section and elevation drawings have heights that are in harmony with each other.

Figure-8: Viewing and measuring in FARO Scene2Go app – example 1.

Figure-9: Viewing and measuring in FARO Scene2Go app – example 2.

Geo-Mat3D, surveys with a high accuracy and precision all and any structures by using the most appropriate and right measuring technique. In order to overcome the challenges arising in projects, it attains optimal solutions by using integrated measurement techniques correctly and properly without compromising data accuracy.