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Geoinformatics-8-2008
article cad systems, the total s_go can be consistently combined via boolean operations. with database information attached, s_go can then be subject to concurrent spatial and attribute queries in 3d. changes in s_go portraying a geotechnical project means keeping track of a dynamic system with s_go changes being mostly project-related: the advancement of a tunnel, the excavation of a building pit, drilling and grouting activities, etc., will change both the s_ngo and the s_tgo ensembles. to a lesser extent, natureinduced changes also have to be considered - e.g. ground water level variation. the consistent incorporation of change in geometry and shapes of associated s_go objects is a particular challenge for the geobim concept (compare figure 3). geobim - application range and advantages whenever a new building is going to be constructed, all relevant subsurface objects have to be considered. in construction projects a sound knowledge of position, geometrical shape and properties of subsurface objects is necessary. this pertains to all phases of a subsurface building s life cycle: pre-design, design, construction and operation stages. as mentioned above, subsurface objects can either be natural objects (geology, hydrogeology), or existing or planned technical objects such as cables, drain pipes or tunnels. in order to adapt the building to local conditions and to achieve secure and cost-effective construction, designers and engineers have to consider these subsurface objects at the same time. access to all data concerning location, shape and properties of relevant subsurface objects, as well as data quality (statistical information) is of prime importance for the experts involved during the entire project. in tunnelling, this need is expressed by several concurrent development activities of 3d tunnelling documentation software. a geo building information modelling approach enables the full, digital representation of the building process and facilitates the exchange and interoperability of data. typically, a geobim data set comprises complexly-shaped, natural objects as well as the relatively simple shapes of man-made objects. providing a development platform for design and administration tools of geospatial and geotechnical projects, the location, geometry figure 2: subsurface geo building modelling framework - geobim. see text for detailed explanation. tion, s_ngo diversify and have a range from micro- to macro scale. therefore, the elements of these categories can be further separated into several components (this clearly is application dependent a tunnelling project in sediments will be based on different design criteria than one in hard rock), with a range from minerals to lithological units for example. examples for s_ngo are lithological units like gravel, marble or a shear zone, or a groundwater body (see fig.1). in any engineering project, besides s_ngo, technical subsurface objects exist. we call these technical objects subsurfacetechnicalgeoobjects ( s_tgo ). such objects are for example all elements of subsurface infrastructure facilities like pipes, wiring, caverns, galleries or tunnels and the subsurface components of any building (e.g. a foundation, a subsurface parking area etc.). during construction of these technical objects, information about s_ngo is acquired by exploration. s_ngo and s_tgo together make up the geobim modelling framework (see figure 2). subsurface modelling: b-rep objects with database links while geometrical solid models portraying s_tgo are the by-product of any up-to-date, cad-based planning process, data on s_ngo typically have to be acquired in the pre-project phase by exploration. usual data sources are mapping, remote sensing, geophysics and drilling. to be able to automatically interact with technical subsurface geo objects, natural subsurface object data have to be transformed into solid models of s_ngo. the industry s standard approach to geometrical solid modelling is b-rep (7), which is offered by cad systems. providing nurbs functionality, current cad systems (e.g., autocad, microstation, catia) are able to portray the complex shapes of s_ngo in addition to the geometrically straightforward s_tgo. in these figure 3: location, shape, properties and number of s_go changes. any technical activity will change the s_ngo and s_tgo ensemble of a geobim. latest news? visit www.geoinformatics.com 41 december 2008
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