III. LA EDAD MODERNA
1. EL SIGLO XV EN ITALIA a) Introducción
The client is currently parking at a street corner and would like to establish a carport within the property line. The ‘L’ shape street corner is located on a hillside, the steep slopes are indicated with red arrow on Figure 53. According to the requirements of the city council the floor level of the carport should be slightly below the street level and the rainwater from the roof of the future building should be drained to the existing stormwater pipe.
The ‘Dial-before-you-dig’ map indicated that although the stormwater pit #34 grate is positioned in a lower level, then the #32A, the water inside the pipeline below the surface is flowing from #34 toward #32A. In order to be able to determine the flow of the rainwater and establish the required floor level (FL) of the future building a detailed land surveying plan was required.
Figure 53 The site of the future cross-over and carport. The ‘Dial-before-you-dig’ map indicates the existing stormwater pipes (Source: TheLIST and ‘Dial-Before-You-Dig)
Future Carport TBM
_______________________________________________________________________________________________________________ 6.2 Data Acquisition
As a first step a TBM was established. The height value and the Easting-Northing position of the TBM was determined with a CORS36 corrected RTK37 GPS equipment using nearby Survey Control Marks. In this case the TBM could have an arbitrary height value, but the GPS was available and the procedure took less than half an hour. Another half an hour was allocated to taking a series of photos of the site using Canon 600D DSLR38 camera with a 35 mm lens. Also the distances between nominated control points and the dimensions of the existing stormwater pits were measured using Leica Disto-A5 (DISTO) digital distance measurement tool. The images were processed into a dense point-cloud later in the office using Agisoft PhotoScan photogrammetry software (http://www.agisoft.com/ ).
At that point of time it was not clear which points of the streetscape will be relevant, hence the whole area was recorded employing close range photogrammetry. The software semi automatically listed the Easting, Northing (MGA) and AHD values of the pre-selected points of the dense point-cloud (Figure 54). These points were used as survey observations in order to create the 3D model of the footpath and the driveway. Although the PhotoScan is able to export the data into LAS file format or 3D PDF as well, in this example the dense point cloud was used as a real-size, measurable 3D virtual model of the area of interest.
36 Continuously Operating Reference Stations 37 Real-time Kinematic
38 Digital Single–Lens Reflex camera (https://store.canon.com.au/en/Our-Products/Digital-Cameras/EOS-Digital-SLR-Cameras/EOS-600D) Figure 54 Screen capture images of the point-cloud scene created by PhotoScan
software. The Easting, Northing and the AHD values of the nominated points are marked with ‘blue flags’ and listed on the screen. (Created by: F. Acs)
6.3 Terrain modelling and the Design Procedure
The survey observation data and an architectural BIM authoring software, ArchiCAD 19, were used to construct the 3D model of the existing terrain and design the carport and the crossover. The virtual model of the design and the terrain of future building was constructed simultaneously. Although a proper BIM model of the project was constructed, the 3D modelling was used only to demonstrate the flow-path of the rainwater for the planning department officials. The Development Application required traditional 2D drawings. While the design was presented in animated 3D PDF as well, only the screen-capture images of the 3D model were carefully interrogated by the authorities. The pictures were captured from several angles such as top-view, bird-eye view, and worm’s eye view. Although the surface topography was an important guideline, the 3D terrain model was set to be see-through in order to be able to assess the objects below the surface. The structure and the geometry of the carport is accurate, the properties of the building materials are indicative, the shadow casting is realistic (Figure 55). All the 2D components, sections, elevations and plans were derived directly from the 3D model and submitted in PDF file format.
Figure 55 The 3D model of the design was used to demonstrate the rainwater flow
_______________________________________________________________________________________________________________ 6.4 Design workflow
The design of a crossover and a carport seems to be a task for an architectural office. In an ideal world however the land surveying office should produce the 3D terrain model and the initial 3D design model of the crossover and the stormwater management. The 3D model of the design sent as an IFC file to the designer, where the footings, the walls and the roof structure is added to the package. The engineer corrects or approves the details of the structural elements. The improved package is finalised at the building surveyor’s office where the design receives the final touch for submission. This was not the case during this project. All the survey, design and model crafting tasks were prepared, executed and presented by the same AEC professional, as is often the usual practice for a small project.
6.5 Data Presentation – Data Transfer
The modelling and the visualisation components of the BIM authoring software was used in this project. The 3D parametric design capabilities were mainly utilised to accelerate the terrain and building modelling, the software was essentially emulating a CAD software package. If data transfer occurred, it was done with the same computer. As it was indicated, the results were translated to PDF file format and submitted or distributed via Internet.
6.6 Summary
This case study described above demonstrates that when land surveying and the design procedure collaborate via 3D modelling then even a small project can be completed efficiently. Neither the site survey, nor the design procedure required more time than the traditional workflow practice would indicate. The 3D screen captures described the stormwater management clearly and helped to reduce the lengths of the Development Application approval procedure. These images were also successfully re-used during the budget negotiation with the builder.