Application of urban building completion survey?

1 project overview and operation process

1. 1 Project Overview Guangzhou Nanfeng International Convention and Exhibition Center is located in Pazhou Island, Haizhu District, Guangzhou, including Nanfenghui Global Convention and Exhibition Center and Nanfeng International Convention and Exhibition Center * *. It is a modern business center integrating commercial office buildings and five-star hotels with a total construction area of 283,000m2, as shown in figure 1. The appearance of the exhibition center is unique and fashionable, and it is staggered layer by layer; The design of the tower is like the random and disorderly stacking of squares, and each square, that is, each floor, is stacked in disorder and order; The skirt building design has the beauty of outward or inward inclined lines. Because of its modern geometric elevation structure, it is difficult to accurately measure the plane position of each floor of the podium slope, the plane position of each floor of the staggered-floor tower and many concave angles between the podium slope and the "square" of the tower by using the total station, which brings challenges to our traditional planning acceptance measurement.

1.2 operation flow in view of the above analysis of the completion acceptance of the special-shaped building of the convention and exhibition center, the project team used the three-dimensional laser scanning technology to measure its completion acceptance. Its operation flow is shown in Figure 2, and its main contents include: control survey, field scanning survey, indoor data processing, as-built drawing inspection, three-dimensional modeling, building area calculation, plane elevation, as-built topographic map, etc.

2 3D completion survey data acquisition

2. 1 control survey In order to meet the requirements of the planning and acceptance of construction projects for measurement accuracy, this project has laid out a first-class static GPS control network and four static control points to cover two buildings, and the fourth-class leveling is 8km in parallel (as shown in Figure 3). The starting point of the first-level control network is the third-level plane control point in Guangzhou near the project. In order to improve the accuracy of the whole network, the starting point covers four primary control points, and the elevation control starts from the nearby secondary bedrock level control point. Using the first-class GPS control network and the fourth-class leveling can not only ensure the accuracy of the planning acceptance control survey, but also access the acceptance survey results to the Guangzhou plane coordinate system and height system.

2.2 laser scanning measurement data acquisition RIEGLVZ-400 3D laser scanner is adopted in this project, and its reflection distance is 500m. According to the special-shaped features of the convention and exhibition center building, this 3D laser scanning mainly adopts the following two modes: ① Single-station absolute orientation mode: three-dimensional laser scanning stations and targets (similar to the prism of total station) are arranged at the root point of the map, and scanning parameters are set for scanning. ② Target-free relative orientation: directly scan the target building in a target-free manner. Coordinate measurement of scanning station Using Guangzhou Continuous Operation Satellite Positioning Urban Survey Integrated Service System (GZCORS) and Guangzhou Quasi-geoid, the built-in GPS positioning function of 3D laser scanner is developed, which enables 3D laser scanner to measure RTK coordinates of scanning station while scanning buildings, thus improving the speed of field operation and indoor registration efficiency.

3 3D completion survey data processing

3. 1 Pre-processing of scanning measurement data After building scanning is completed, point cloud data needs to be pre-processed, including point cloud denoising and point cloud registration. The original point cloud data obtained by (1) point cloud denoising and repairing will produce a large number of holes and noises due to shrub occlusion, self-occlusion, glass transmission and other reasons, resulting in poor quality of the original point cloud, so it is necessary to denoise and repair the holes. Firstly, the noise with large deviation is removed in RiscanPro, the supporting software of the ground 3D laser scanner, and then the noise is further removed and the holes are filled by interactive operation in GeomagicStudio.

(2) Point cloud data registration is based on two methods of field data collection, and data registration also adopts two corresponding modes. (1) Backward-looking directional registration: initial station and target are registered, station coordinates and target coordinates are input, and the backward-looking directional registration module in RieGLRiscan is used for registration, so as to determine the global coordinates of the whole point cloud data. (2) First, do a good job of registration between stations, which can be done in two ways: a. The method of selecting feature points with the same name is suitable for points with obvious features, at least four points with the same name are selected, and sharp features such as house corners and telephone pole tops are selected as far as possible; B, according to the manual interactive mobile station, move the unregistered station to the corresponding position of the registered station, and the matching accuracy shall be subject to automatic and accurate matching. After the rough matching is completed, the software is used to automatically and accurately match and improve the registration accuracy. Only when the registration error is within 0.0 1m can the next site be registered. As shown in Figure 5, the building point cloud data map of Nanfeng International Convention and Exhibition Center after data registration.

3.2 Calculation of Building Area (1) The characteristic line is extracted by slicing method, the appropriate slicing thickness is designed, and the registered 3D point cloud data of each floor is processed by X-Y horizontal section, and the characteristic line of each floor of the building is obtained by extracting the characteristic points, so as to calculate the building area of this floor. (2) For the calculation of building area, the characteristic lines of each layer are extracted by slicing method, the drawing exchange file (dxf format file) is output, and the CAD software is imported to draw the building line diagram in the editing state of data engineering, so as to calculate the building area.

3.3 Drawing of elevation According to the requirements of building completion acceptance, it is an important job to check the elevation of building completion. Comparing the completed elevation of this project based on scanned point cloud data with the completed elevation provided by the construction unit, we can clearly understand the actual size of the elevation, which is in line with the field situation. The drawing process of the elevation of this project is shown in Figure 6. Laserscanner, a software independently developed by the project team, is used to project the three-dimensional model of point cloud data on the main elevation, and the three-dimensional measurement mode is adopted to measure, and the dxf file is exported and imported into CAD software. Under the planning and management project template, the elevation line is drawn according to the high-definition pictures obtained by the high-resolution digital camera of the ground LiDAR component. Three-dimensional laser scanners are used to measure the completion of buildings. One of the final products is to establish a three-dimensional model of the target object, as shown in Figure 7, from which the cross section can be extracted for measurement and area calculation. According to the modeled point cloud, the completed elevation of the tower is drawn, as shown in Figure 8.

4 Result analysis

Take the 9th floor of Nanfeng International Center as an example (Figure 9). The figure below shows the point cloud plan taken from the X-Y horizontal section and compared with the total station observation data (the red line is the total station observation). In this project, the ground 3D laser scanner is combined with total station observation. Taking the ninth floor of Nanfeng International Convention and Exhibition Center as an example, the point cloud data is filtered and denoised again, and connected into a line, and compared with total station observation. See table 1 for the coordinates of each corner. Because the centers of the two towers are hollow, the peripheral area of the ninth floor of Nanfeng International Convention and Exhibition Center is 3 134.0km2 (excluding the hollow area), and the calculated area of the three-dimensional laser scanner is 3 133. 1 km2, with little difference.

5 abstract

With the increase of special-shaped buildings and the complexity of planning and management in the process of urbanization, the traditional two-dimensional completion survey can no longer meet the requirements of planning and management. With its own technical characteristics, 3D laser scanner can obtain some corners of buildings that are difficult to be collected by total station. Taking a special-shaped building in Guangzhou Convention and Exhibition Center as an engineering example, this paper verifies the feasibility of three-dimensional laser scanning technology in urban building completion survey. Firstly, the working process of 3D completion survey is summarized, then the data acquisition process and technology of control survey and laser scanning survey in 3D completion survey data acquisition are introduced, and finally, the three key processes of scanning survey data preprocessing, building area calculation and elevation drawing in 3D completion survey data processing are analyzed and studied. Through the comparative analysis of three-dimensional completion measurement data and total station observation data, there is little difference between point and surface results, which can meet the needs of building completion measurement. To sum up, this paper thinks that 3D laser scanning technology has good application value in the acceptance measurement of complex and super-large buildings, and should be popularized in the specific planning acceptance.

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