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Copyright Protection of Digital Images of Cultural Heritage
Published in Filippo Stanco, Sebastiano Battiato, Giovanni Gallo, Digital Imaging for Cultural Heritage Preservation, 2017
Filippo Stanco, Sebastiano Battiato, Giovanni Gallo
Simplification. Mesh simplification, also referred to as decimation, regards the reduction of the number of vertices and triangles of a polygonal mesh model while preserving its shape. Typically, an atomic simplification operation is defined and applied several times to obtain the simplified mesh. An example of atomic simplification is the removing of a vertex with a successive retriangulation of the produced hole. The sequence of atomic simplification steps to apply to the model is built using a similarity metric. The similarity metrics measure the impact of each atomic step and determine the quality of the simplified output mesh. Such metrics can be of two types: geometric and image-based. Some examples of algorithms that use geometric metrics are [13,25], and image-based metrics are [42,45,67]. This kind of processing can be considered as a non-malicious attack when it is applied to optimize the mesh, i.e., to eliminate over-sampling of the model’s surface.
Software Phantoms for X-ray Radiography and Tomography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
NURBS have an advantage in respect to the anatomic realism and the spatial deformation, and in fact it takes advantage of the most desirable features of both the mathematical and the voxel phantoms. This technique offers mathematical approaches for representing not only standard analytic shapes, but free-form curves and surfaces, many of which are very appropriate for describing complex tissue structures. This feature facilitates the easier modification of organ volumes and body contours, as well as to adjust body stature, and at the same time it provides a significantly higher degree of anatomical realism achieved, compared to what is possible with either stylized or voxel phantoms. An example is modeling of the lung with a smooth surface and continuous in all dimensions. Some of the more challenging tissues to model in a voxel phantom are the facial bones of the skull. NURBS surfaces are advantageous over polygon meshes, since they can model objects using smaller number of parameters. While a polygon mesh of an object may contain tens of thousands of vertices, a NURBS surface may model the same object with the same level of accuracy using just 100 to 200 control points. However, for some organs such as the spine, a polygon mesh model is used to retain the finer complexities of its 3D structure (e.g., vertebral processes and bodies).
Decimation and smoothing of triangular meshes based on curvature from the polyhedral Gauss map
Published in João Manuel, R. S. Tavares, R. M. Natal Jorge, Computational Modelling of Objects Represented in Images, 2018
The most common representation for an object in computer aided applications, specially in 3D graphics, is still the polygonal mesh, where a collection of points in space are joined together by edges and faces to form a shape. This provides great flexibility in representing a variety of shapes, from simple to very complex ones, and in varying degrees of detail. Modern methods for generating 3D objects involve high definition scanning of data, providing very detailed meshes of the target objects. Often this produces an enormous amount of data, which is difficult to handle by current computer systems for application in real time. Meanwhile, the data acquired with these methods may be redundant or excessive to portray the shape of the object.
When a tree model meets texture baking: an approach for quality-preserving lightweight visualization in virtual 3D scene construction
Published in International Journal of Digital Earth, 2023
Chen Zhang, Biao He, Renzhong Guo, Ding Ma
Numerous approaches have been proposed in the field of 3D model processing. A common processing method for reducing the data size of geometries is mesh simplification (Burghardt and Cecconi 2007; Chen, Li, and Li 2015; Li and Nan 2021; Tariq et al. 2021). Mesh simplification algorithms transform a given polygonal mesh into another mesh with fewer faces by removing vertices or resampling. Although mesh simplification can accelerate vision algorithms by generating more compact geometry models, an oversimplified mesh may change the structure of a model such that the model cannot properly maintain texture mappings (Cohen, Manocha, and Olano 2003; She et al. 2022). Another limitation associated with mesh simplification lies in the ability of the model to preserve details. Mesh simplification maintains the main structures of a mesh but may obscure the underlying morphological details (Merlo et al. 2013). For old and valuable trees, it is difficult to obtain the desired models with pure mesh simplification. In texture processing, reducing the texture resolution is an effective method for optimizing model storage and transmission (Wolski et al. 2019). Several application instances, such Unreal Engine 4 and Unity, build mipmaps of a model by converting high-resolution textures into low-resolution textures, which support texture streaming for fast model loading (Beers, Agrawala, and Chaddha 1996). Nevertheless, low-resolution textures will obviously lead to a blurred surface where pixels cannot convey the precise color of the original model.
Digital Twinning remote laboratories for online practical learning
Published in Production & Manufacturing Research, 2022
C. Palmer, B. Roullier, M. Aamir, F. McQuade, Leonardo Stella, A. Anjum, U. Diala
Digital Twin Builder utilizes polygonal meshes to enable real time rendering. Polygonal meshes are a lightweight means of representing arbitrary 3D geometry, and are commonly used in real-time applications such as 3D video games and animations (Akenine-Moller et al., 2018). A polygon mesh approximates an object as a finite set of vertices and polygons (triangles). A greater number of polygons produces a more accurate approximation of the real object at the expense of increasing the computational burden required to render that approximation. As such, the creation of meshes for use in a digital twin is often a trade-off between visual accuracy and performance considerations. In traditional digital twin production, geometry is created by skilled 3D artists. This is one of the largest expenses in the production process. In order to reduce these costs and open up digital twins for use in teaching environments, an economical means of creating accurate polygonal meshes is required.
Creation of 3D printed fashion prototype with multi-coloured texture: a practice-based approach
Published in International Journal of Fashion Design, Technology and Education, 2021
Ivonbony Chan, Joe Au, Chupo Ho, Jin Lam
Three-dimensional printing is an additive manufacturing technique to create a solid object. During the manufacturing process, materials are successively assembled on one cross-sectional layer at a time, with the final product comprising many layers (Campbell et al., 2011). The process starts with a 3D digital model that is generated on a computer by using different types of 3D drawing software programs and is referred to as CAD. A software program slices the model into layers and converts the layers into readable files for a 3D printer; subsequently, materials are added layer-wise by the printer to form a 3D object. Three-dimensional virtual objects are created by a combination of 3D modelling, texturing and rendering in CAD design. In the 3D modelling process, polygon mesh and polygons can be assembled together to form shapes. Texture mapping is a method to add illusive textures on 3D virtual objects, whereas texture can be images of pictures or hand paintings. During the rendering process, the texture meshes are unwrapped to one flat image, then texture is projected onto the meshes (Ahearn, 2014; Mullen, 2011). Rendering is a mathematical process to calculate every pixel of the virtual object to produce a final image (Murdock, 2012).