43 research outputs found
Non-square grids: A new trend in imaging and modeling?
No full textThe raster format of images and data is commonly intended as a synonymous of a square grid. Indeed, the square is not the only shape that can tessellate the plane. Other grids are well-known, and recently they have moved out of the fields of art and mathematics, and have started being of interest for technological applications. After introducing the main types of non-square grids, this paper presents experiences of practical uses of non-square grids, especially the hexagonal one, in various fields, including digital imaging, geographic systems, and their applications in sciences like medicine, environmental monitoring, etc. We conclude with considerations on the state of the art and perspectives for the future. In our opinion, the research is mature enough to prefigure a broader diffusion of some non-square grids, especially the hexagonal one
Compressing TINs
No full textWe address the problem of designing compact data structures for encoding a Triangulated Irregular Network (TIN) as a sequential bitstream. In particular, we study the problem of compressing connectivity, i.e., the information describing the topological structure of the TIN and we propose two new compression methods which have different purposes. The goal of the first method is to minimize the number of bits needed to encode connectivity information: it encodes each vertex once, and requires two bits of connectivity information for each edge of a TIN. We present efficient algorithms for coding and decoding the corresponding bit-stream and show some practical evaluation of the method. The second method compresses a TIN at progressive levels of detail and is based on a strategy which iteratively removes a vertex from a TIN according to an error-based criterion. Encoding and decoding algorithms are presented and compared with other approaches to progressive compression
Elettromanometria ano-rettale nella malattia di Hirschsprung e diagnosi enzimo-istochimica.
No full textElettromanometria ano-rettale nella malattia di Hirchsprung e diagnosi enzimo-istochimica
No full text
Chirurgia ricostruttiva dell’esofago e trattamento conservativo nella stenosi esofagea da caustici
No full textMulti-VMap: a Multi-Scale Model for Vector Maps
No full textMulti-VMap is a compact framework from which plane graphs representing
geographic maps at different levels of detail can be extracted. Its main
feature is that the scale of the extracted map can be variable through its
domain, while each entity maintains consistent combinatorial relations with
the rest of entities represented in the map. The model is based on a set of
operators, called updates, which modify the level of detail in a small
portion of a map. The set of updates is partially ordered, and can therefore
be represented as a Directed Acyclic Graph, which defines our multi-scale
structure. An algorithm to extract a map at the required resolution is
proposed, and a lower bound for the number of different maps which can be
extracted from the model is given. The model supports map data processing
operations (e.g., querying), as well as progressive and selective
transmission of maps over a network
Discrete Morse versus Watershed Decompositions of Tessellated Manifolds
No full textWith improvements in sensor technology and simulation methods, datasets are growing in size, calling for the investigation of efficient and scalable tools for their analysis. Topological methods, able to extract essential features from data, are a prime candidate for the development of such tools. Here, we examine an approach based on discrete Morse theory and compare it to the well-known watershed approach as a means of obtaining Morse decompositions of tessellated manifolds endowed with scalar fields, such as triangulated terrains or tetrahedralized volume data. We examine the theoretical aspects as well as present empirical results based on synthetic and real-world data describing terrains and 3D scalar fields. We will show that the approach based on discrete Morse theory generates segmentations comparable to the watershed approach while being theoretically sound, more efficient with regard to time and space complexity, easily parallelizable, and allowing for the computation of all descending and ascending i-manifolds and the topological structure of the two Morse complexes
