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The origins of BIM in computer-aided design
Published in Ray Crotty, The Impact of Building Information Modelling, 2013
The objective in the process called lofting is to take the lines drawing information and scale it up to full size, either on a 1:1 scale drawing, or directly onto the sheet material from which the hull will be built, so that the plywood, steel, or other material can be cut accurately. To do this the overall rectangular grid of the hull is first drawn out precisely. The contours are added to the drawing or hull sheeting by fixing pins, or blocks called ducks, at the points on the full-scale drawing, or the material sheet, corresponding exactly to the locations of the stations given in the table of offsets. These station points are then joined up smoothly, so as to give a fair contour line on the hull. This is done by threading a strong flexible strip of wood or metal, called a spline, along the sequence of pins. The spline comes to rest in a form that is made up of shapes of minimum strain energy between each of the station points. The contour is drawn tracing the line that the spline follows onto the underlying material. This creates a smooth interpolation of points between successive stations on the contour line. The result is an approximation to the original contour on the lines drawing, close enough to the original to generate a fair line, but requiring far less calculation and measurement than a true copy would require.
ANSYS: Finite Element Analysis
Published in Paul W. Ross, The Handbook of Software for Engineers and Scientists, 2018
Because the solid model representation is NURBS-based in the ANSYS program, users can take advantage of a surface construction technique known as “skinning” or “lofting” (Fig. 58.15). With this technique, the user can define a set of cross sections in the model, including curves, and instruct the program to automatically generate a surface that fits through those cross-sections. This skinning technique can help facilitate modeling of complex shapes.
Point cloud slicing for 3-D printing
Published in Computer-Aided Design and Applications, 2018
William Oropallo, Les A. Piegl, Paul Rosen, Khairan Rajab
Object slicing has been around since the advent of CAD techniques in design and manufacturing. In the early days complex objects, such as a ship hull or an airplane fuselage, have been sliced into cross sections, with some distance apart, and a skin was pulled over the sections to complete the design. The method was termed lofting [15] because it needed so much space that it was done in the loft. As time went on, lofting became a powerful tool to model incredibly complex objects; it became the scan-line method of CAD, borrowed from the scan-coherence principle of computer graphics. It has been rediscovered from time to time [17] to aid in design and fabrication of virtually any objects from household items to entire buildings. 3D printing is, effectively, the consequence of decades of cross-sectional practices where the slices are stacked on top of each other instead of keeping them apart, and eliminating the need to generate the skin.