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Design-to-design exchange of bridge models using IFC: A case study with Revit and Allplan
Published in Jan Karlshøj, Raimar Scherer, eWork and eBusiness in Architecture, Engineering and Construction, 2018
In Building Information Modeling, two different approaches can be distinguished in modeling volumetric bodies (so called Solid Modeling). The first one—Explicit Modeling, known as Boundary Representation, describes a body in terms of its bounding surfaces. The basic principle is that the bounding surfaces, called Faces, are described by Edges, and they, in turn, are depicted by Vertices. The whole system of relationships between them is denoted as the topology of the modeled body. An alternative approach to Solid Modeling—Implicit Modeling—is based on a sequence of construction steps to describe a resulting volume. The approach is also known as Procedural Method. The available construction operations include Constructive Solid Geometry (CSG) operations as well as sweeps and extrusions. CSG employs the predefined geometric primitives (such as cubes, cylinders and pyramids) and combines them using the Boolean operators (such as union, intersection, and difference). The output is a more complex body, which can be used in further construction steps. Another example is an extrusion which is defined by a planar profile extruded along a desired vector (Borrmann and Berkhan, 2018).
Software Phantoms for X-ray Radiography and Tomography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
The CSG allows the creation of solid objects by using a Boolean operator to combine simple geometrical primitives, either based on quadrics such as cylinders, ellipsoids, cones, semi-ellipsoid, or a set of polygons like cuboids, pyramids, prisms, and so on. The first four surfaces (Figure 57.2a) are easily described by quadric equations. Quadrics are surfaces defined by second-order polynomial equations of three independent variables, x, y, z: Ax2+Ey2+Hz2+2Bxy+2Fyz+2Cxz+2Dx+2Gy+2Iz+J=0
The origins of BIM in computer-aided design
Published in Ray Crotty, The Impact of Building Information Modelling, 2013
The data from these surface modelling systems can be passed to a variety of capable of milling or pressing large complex curved surfaces. The second big problem for manufacturers was how to model solid objects like engine blocks, and assemblies of objects like machine guns. Perhaps because solid modelling is more conceptually difficult or computationally demanding, it was not until the 1970s that the first solid modelling systems were released. There are many different approaches to the problem of modelling a solid object; the two most widely used techniques are constructive solid geometry (CSG), and boundary representation (BREP). A CSG model is created by performing Boolean set operations – union, intersection and difference – on primitive solid shapes, such as cones, pyramids, cylinders and cuboids. BREP, as the name suggests, works by tracing and recording the edges or boundaries and vertices of solid forms. CAD systems typically combine elements from both of these.
Method of Characteristics for 3D, Full-Core Neutron Transport on Unstructured Mesh
Published in Nuclear Technology, 2021
Derek R. Gaston, Benoit Forget, Kord S. Smith, Logan H. Harbour, Gavin K. Ridley, Guillaume G. Giudicelli
While CSG is ideal for ray tracing, it can be difficult to use for representing complicated geometries and geometric deformation.28 An alternative is unstructured mesh. Most commonly used in finite element solvers, unstructured mesh builds geometry out of discrete “elements” that are made of simple shapes such as triangles, quadrilaterals, hexahedra, and tetrahedra. Many of these small elements can be combined to create complicated geometries that can then be straightforwardly deformed. This is the approach MOCkingbird uses for geometrical representation. In addition to the flexibility gained through utilizing unstructured mesh, by abstracting ray tracing to be across an element, MOCkingbird gains the ability to work in 1D, 2D, and 3D. Unstructured mesh is also the basis for numerous non-MOC finite element transport solvers.29,30
On the visual reality and monitoring of gantry cranes using FBG sensing
Published in Australian Journal of Mechanical Engineering, 2021
Hang Su, Tingling Chen, Yusi Zhang
Constructive Solid Geometry (CSG) is one kind of physical modelling based on a set theory. Complex elements are constructed by intersecting or differentiating simple elements, such as cuboid, cylinder, cone, frustum, rings and balls. Boolean operations are pairwise. An entity may be represented as a binary CSG tree, where the leaf node is the basic element and the intermediate node is Boolean. The information in CSG modelling is very simple and convenient to process. This method records all the initial features and parameters of forming a geometric object. The presented geometric objects own the benefits of uniqueness and clarity. CSG focuses on actual graphs and constructs the shape of the parts that are actually operating without considering internal details of real machinery. It classifies the modelling structure layer by layer. The whole geometric model is built on the relation of ‘Models basic elements – structural units – Structure – machinery and equipment’.
A voxel-based method for designing a numerical biomechanical model patient-specific with an anatomical functional approach adapted to additive manufacturing
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Augustin Lerebours, Frederic Marin, Salima Bouvier, Christophe Egles, Alain-Charles Masquelet, Alain Rassineux
Computer-assisted design (CAD) systems are mostly based on two kinds of modelling, namely Constructive Solid Geometry (CSG), and Boundary representation (B-rep) (Mäntylä 1987). CSG modelers allow the creation of objects that combine simpler objects known as primitives (cones, sphere, cuboids, pyramids), using Boolean operators. CSG has the advantage of ensuring that objects are ‘solid’, or watertight. It also provides a quick way of creating geometries, but surface representation may not be accurate enough when the objects to be represented have complex 3D shapes, which is generally the case for anatomical structures (Mäntylä 1987). B-rep, on the other hand, allows a local representation of connecting faces, edges and vertices through simple geometric items (points, curves and surfaces). B-rep is therefore more flexible and often yields an accurate 3D representation. However, it requires more sophisticated CAD skills, particularly when making the model watertight, as there are no algorithms for topological operators (Mäntylä 1987). All the modelling therefore has to be done manually, which is time-consuming.