From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Direct slicing <s> The 3D Systems stereolithography file format is a good workhorse for the rapid prototyping (RP) industry. It is supported by all major computer‐aided design (CAD) and RP manufacturers and there now exists a selection of third‐party software which supports this de facto standard and helps to make it work better. However, input to RP systems is sometimes best suited to the format of sliced contours. These may be produced from a three‐dimensional CAD model or via reverse engineering techniques such as laser scans and co‐ordinate measuring machines. Other sources include computed tomography and magnetic resonance imaging scans. Takes a brief look at both of the above methods, listing their advantages and disadvantages. Identifies several ways in which sliced data can be used to drive RP processes. Finally, presents in detail a methodology used to develop a direct and adaptive slicer from a commercial CAD system. <s> BIB001 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Direct slicing <s> AbstractRecently point set model is getting increasing research attention in many geometric modeling application areas including computer graphics and CAD/CAM. This paper presents a novel approach to directly slicing point set model with the focus on making rapid prototyping part out of point set model without making any mesh or surface. Main challenge in handling point set model lies in how to interpret inter-point empty space and implicit quadric surfel is used in this research. This paper also explains how to utilize the quadric surfel for slicing the point set, so as to obtain contour curves for RP. Also described in this paper is how to extract smooth curve(s) out of the 2D point cloud obtained by slicing the 3D point set model. <s> BIB002 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Direct slicing <s> Rapid advancement of 3D sensing techniques has led to dense and accurate point cloud of an object to be readily available. The growing use of such scanned point sets in product design, analysis, and manufacturing necessitates research on direct processing of point set surfaces. In this paper, we present an approach that enables the direct layered manufacturing of point set surfaces. This new approach is based on adaptive slicing of moving least squares (MLS) surfaces. Salient features of this new approach include the following: (I) It bypasses the laborious surface reconstruction and avoids model conversion induced accuracy loss. (2) The resulting layer thickness and layer contours are adaptive to local curvatures, and thus it leads to better surface quality and more efficient fabrication. (3) The curvatures are computed from a set of closed formula based on the MLS surface. The MLS surface naturally smoothes the point cloud and allows upsampling and downsampling, and thus it is robust even for noisy or sparse point sets. Experimental results on both synthetic and scanned point sets are presented. <s> BIB003 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Direct slicing <s> Direct slicing of point cloud is an effective way to integrate reverse engineering and rapid prototyping. However, since the input of the direct slicing process is discrete point data, connections between the points are absent. The lack of global structure may make the process fail to handle complex shapes that have multicontoured slices. Furthermore, it may cause accuracy loss at some important features, e.g., at topology transitions. In order to overcome the above limitations, this paper presents a method to extract topological structure from the point cloud and applies the structure into a moving-least square (MLS) surface-based direct slicing process. In addition to the topology extraction, two modifications are made to improve the efficiency and stability of the process: (1) a variation of the traditional projection-based MLS surface is adopted; (2) a rectification algorithm is presented in 2D contour generation to avoid biased curves when abrupt curvature changes happen. The improved direct slicing method is tested by some case studies including synthetic and scanned data. The efficacy of the algorithm is demonstrated by the results. <s> BIB004 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Direct slicing <s> Growing use of massive scan data in various engineering applications has necessitated research on point-set surfaces. A point-set surface is a continuous surface defined directly with a set of discrete points. This paper presents a new approach that extends our earlier work on slicing point-set surfaces into planar contours for rapid prototyping usage. This extended approach can decompose a point-set surface into slices with guaranteed topology. Such topological guarantee stems from the use of Morse theory based topological analysis of the slicing operation. The Morse function for slicing is a height function restricted to the point-set surface, an implicitly defined moving least-squares (MLS) surface. We introduce a Lagrangian multiplier formulation for critical point identification from the restricted surface. Integral lines are constructed to form Morse-Smale complex and the enhanced Reeb graph. This graph is then used to provide seed points for forming slicing contours, with the guarantee that the sliced model has the same topology as the input point-set surface. The extension of this approach to degenerate functions on point-set surface is also discussed.Copyright © 2010 by ASME <s> BIB005
To avoid having to re-sample the CAD model into a triangle mesh or ray-rep, several techniques have been proposed to extract contours directly from the initial geometry. These approaches directly output slice data to the printers. The slice file format is often vendor-dependent, but some independent formats such as CLI (Common Layer Interface) can be used. Open source printers often accept slice data (e.g. G-Code for filament printers or images for DLP printers such as the B9Creator or Autodesk Ember). Jamieson and Hacker BIB001 provide an in-depth discussion of the pros and cons of direct slicing of CAD models for different input types. Non-uniform B-spline surface (NURBS) are a common surface representation in CAD software. Therefore, approaches have been proposed for the direct slicing of NURBS models in order to avoid Techniques have also been proposed for point clouds, which are often obtained from 3D scanners or vision algorithm. They are challenging to print since the connectivity and topology of the surface is unknown. Early methods project points around the 2D slicing plane and reconstruct a contour  WWLZ04, BIB002 . Yang and Qiang BIB003 propose to rely on the moving least square method to implicitly define the surface from the point cloud. Qiu et al. BIB004 and Yang et al. BIB005 refine this approach by considering the global topology of the shape to detect and capture extremal points in an adaptive slicing strategy (see Figure 13) . Chen et al.  propose a complete system for scanning an object and fabricating it in a different location, based on point clouds. This includes a novel support generation algorithm.