Topology Preservation Within Digital Surfaces

International audienceGiven two connected subsets Y X of the set of the surfels of a connected digital surface, we propose three equivalent ways to express that Y is homotopic to X. The rst characterization is based on sequential deletion of simple surfels. This characterization enables us to deene thinning algorithms within a digital Jordan surface. The second characterization is based on the Euler characteristics of sets of surfels. This characterization enables us, given two connected sets Y X of surfels, to decide whether Y is nhomotopic to X. The third characterization is based on the (digital) fundamental group

Topological Theory in Bioconstructivism

In the essay “Landscapes of Change: Boccioni’s Stati d’animo as a General Theory of Models,” in Assemblage 19, 1992, Sanford Kwinter proposed a number of theoretical models which could be applied to computer-generated forms in Bioconstructivism. These included topological theory, epigenesis, the epigenetic landscape, morphogenesis, catastrophe and catastrophe theory. Topological theory entails transformational events or deformations in nature which introduce discontinuities into the evolution of a system. Epigenesis entails the generation of smooth landscapes, in waves or the surface of the earth, for example, formed by complex underlying topological interactions. The epigenetic landscape is the smooth forms of relief which are the products of the underlying complex networks of interactions. Morphogenesis describes the structural changes occurring during the development of an organism, wherein forms are seen as discontinuities in a system, as moments of structural instability rather than stability. A catastrophe is a morphogenesis, a jump in a system resulting in a discontinuity. Catastrophe theory is a topological theory describing the discontinuities in the evolution of a system in nature. A project which applies these models, and which helps to establish a theoretical basis for Bioconstructivism by applying topological models, is a design for a theater by Amy Lewis in a Graduate Architecture Design Studio directed by Associate Professor Andrew Thurlow at Roger Williams University, in Spring 2011. In the project, moments of structural stability are juxtaposed with moments of structural instability, to represent the contradiction inherent in self-generation or immanence. The singularity of the surfaces of the forms in the epigenetic landscape contradicts the complex network of interactions of topological forces from which they result. Actions in the environment on unstable, unstructured forms, and undifferentiated structures, result in stable, structured forms, and differentiated structures

Maintaining authenticity: transferring patina from the real world to the digital to retain narrative value

This research is concerned with utilizing new technologies to harvest existing narrative, symbolic and emotive value for use in a digital environment enabling "emotional durability" (Chapman, 2005) in future design. The projects discussed in this paper have been conducted as part of PhD research by Rosemary Wallin into 'Technology for Sustainable Luxury' at University of the Arts London, and visual effects technology research undertaken by Florian Stephens at University of West London. Jonathan Chapman describes vast consumer waste being "symptomatic of failed relationships" between consumers and the goods they buy, and suggests approaches for designing love, dependency, and even cherishability into products to give them a longer lifespan. 'Failed relationships' might also be observed in the transference of physical objects to their virtual cousins. Consider the throwaway nature of digital photography when compared to the carefully preserved prints in a family album. Apple often use a skeuomorphic (Hobbs, 2012) approach to user interface design, to digitally replicate the patina and 'value' of real objects. However, true transference of physical form and texture presumably occurs when an object is scanned and a virtual 3D model is created. This paper presents three practice-based approaches to storing and transferring patina from an original object, utilizing high resolution scanning, photogrammetry, mobile applications and 3D print technologies. The objective is not merely accuracy, but evocation of the emotive data connecting the digital and physical realm. As the human face holds experience in the lines and wrinkles of the skin, so the surface of an object holds its narrative. From the signs of the craftsman to the bumps and scratches that accumulate over the life of an item over time and generations, marks gather like evidence to be read by a familiar or a trained eye. According to the time and the culture these marks are read within, they will either add to or detract from its value. These marks can be captured via complex 3D modelling and scanning technologies, which allow detailed forms to be recreated as dense 3D wireframe, but the result is often unsatisfying. 3D greyscale surfaces can never fully capture the richness of patina. Authentic surfaces require other qualities such as colour, texture and depth, but there is something else - more difficult to define. Donald A. Norman expands on the idea of emotion and objects by describing three 'levels’ of design "visceral, behavioural and reflective". Visceral is based on "look, feel and sound", behavioural is focused on an object’s use, and reflective is concerned with its message. New technology is commonly seen in terms of its ability to increase efficiency, but this research has longer-term objectives: to repair or even rebuild Chapman's 'broken relationships' and enable ‘emotionally durable' design. The PhD that has formed the context for this paper examines the concept of luxury value, and how and why the value of patina has been replaced by fashion. Luxury goods are aspirational items often emulated in the bulk of mass production. If we are to alter behaviour around consumption, one approach might be to use technology to harvest patina as a way to retain emotional, symbolic and poetic value with a view to maintaining a relationship with the things we buy

Digitally interpreting traditional folk crafts

The cultural heritage preservation requires that objects persist throughout time to continue to communicate an intended meaning. The necessity of computer-based preservation and interpretation of traditional folk crafts is validated by the decreasing number of masters, fading technologies, and crafts losing economic ground. We present a long-term applied research project on the development of a mathematical basis, software tools, and technology for application of desktop or personal fabrication using compact, cheap, and environmentally friendly fabrication devices, including '3D printers', in traditional crafts. We illustrate the properties of this new modeling and fabrication system using several case studies involving the digital capture of traditional objects and craft patterns, which we also reuse in modern designs. The test application areas for the development are traditional crafts from different cultural backgrounds, namely Japanese lacquer ware and Norwegian carvings. Our project includes modeling existing artifacts, Web presentations of the models, automation of the models fabrication, and the experimental manufacturing of new designs and forms

Information hiding through variance of the parametric orientation underlying a B-rep face

Watermarking technologies have been proposed for many different,types of digital media. However, to this date, no viable watermarking techniques have yet emerged for the high value B-rep (i.e. Boundary Representation) models used in 3D mechanical CAD systems. In this paper, the authors propose a new approach (PO-Watermarking) that subtly changes a model's geometric representation to incorporate a 'transparent' signature. This scheme enables software applications to create fragile, or robust watermarks without changing the size of the file, or shape of the CAD model. Also discussed is the amount of information the proposed method could transparently embed into a B-rep model. The results presented demonstrate the embedding and retrieval of text strings and investigate the robustness of the approach after a variety of transformation and modifications have been carried out on the data

Topo-Geometric Filtration Scheme for Geometric Active Contours and Level Sets: Application to Cerebrovascular Segmentation

One of the main problems of the existing methods for the segmentation of cerebral vasculature is the appearance in the segmentation result of wrong topological artefacts such as the kissing vessels. In this paper, a new approach for the detection and correction of such errors is presented. The proposed technique combines robust topological information given by Persistent Homology with complementary geometrical information of the vascular tree. The method was evaluated on 20 images depicting cerebral arteries. Detection and correction success rates were 81.80% and 68.77%, respectively

Methodology for automatic recovering of 3D partitions from unstitched faces of non-manifold CAD models

Data exchanges between different software are currently used in industry to speed up the preparation of digital prototypes for Finite Element Analysis (FEA). Unfortunately, due to data loss, the yield of the transfer of manifold models rarely reaches 1. In the case of non-manifold models, the transfer results are even less satisfactory. This is particularly true for partitioned 3D models: during the data transfer based on the well-known exchange formats, all 3D partitions are generally lost. Partitions are mainly used for preparing mesh models required for advanced FEA: mapped meshing, material separation, definition of specific boundary conditions, etc. This paper sets up a methodology to automatically recover 3D partitions from exported non-manifold CAD models in order to increase the yield of the data exchange. Our fully automatic approach is based on three steps. First, starting from a set of potentially disconnected faces, the CAD model is stitched. Then, the shells used to create the 3D partitions are recovered using an iterative propagation strategy which starts from the so-called manifold vertices. Finally, using the identified closed shells, the 3D partitions can be reconstructed. The proposed methodology has been validated on academic as well as industrial examples.This work has been carried out under a research contract between the Research and Development Direction of the EDF Group and the Arts et Métiers ParisTech Aix-en-Provence