3D free-form modeling with variational surfaces

We describe a free-form stroke-based modeling system where objects are primarily represented by means of variational surfaces. Although similar systems have been described in recent years, our approach achieves both a good performance and reduced surface leak problems by employing a coarse mesh as support for constraint points. The prototype implements an adequate set of modeling operations, “undo” and “redo” facilities and a clean interface capable of resolving ambiguities by means of suggestion thumbnails

Marine accidents in the Brazilian Amazon : the problems and challenges in the initiatives for their prevention focused on passenger ships

The Brazilian Amazon is part of one of the largest river systems in the world, in which the transport of cargo and passengers is commonplace. However, several accidents still occur to passenger ships, causing fatalities. Transportation occurs commonly in remote regions, where there are transport inequalities, and emergency assistance is hard to find. This can affect sustainability in communities with considerable levels of economic and social vulnerability. More information is needed about accidents involving inland transport in the Amazon, to identify the threats to ships and propose strategies for accident prevention. This paper addresses the main problems that long-distance passenger ships face in the Brazilian Amazon, presenting an integrated framework towards accident prevention. First, the present situation is characterized in terms of ship description, spatial distribution, and regulations that are applicable. Next, possible causes of passenger ship accidents are discussed, including topics of concern that should be considered in the Amazon waterways. Finally, measures to help minimize passenger ship accidents are proposed, and the social relevance is discussed. It was found that accidents in the Amazon are due to a combination of human and environmental factors. Stakeholders should strengthen the technical and legal training of ship operators. The use of new technologies for navigational aid and necessary maintenance of ships is suggested. Marine accident prevention initiatives should consider local conditions, such as environmental preservation, cultural respect, and difficulties related to navigation through the complex riverine system of the Amazon region

Orthogonal Polygons as Bounding Structures in Filter-Refine Query Processing Strategies

The use of bounding structures in the form of orthogonal polygons (also known as rectilinear polygons) with a varying number of vertices in contrast with a minimum bounding rectangle (an orthogonal polygon with just 4 vertices in two dimensions) as an object approximation method is presented. Orthogonal polygons can be used to improve the performance of the refine step in the filterrefine query processing strategy employed in spatial databases. The orthogonal polygons are represented using the vertex representation implemented as a vertex list. The advantage of the vertex representation implemented as a vertex list is that it can be used to represent orthogonal polygons in arbitrary dimensions using just their vertices. This is in contrast to conventional methods such as the chain code which only work in two dimensions and cannot be extended to deal with higher dimensional data. Algorithms are given for varying the number of vertices used to represent the objects. It is shown that th..

Vertex Representations and their . . .

The vertex representation, a new data structure for representing and manipulating orthogonal objects, is presented. Both interiors and boundaries of regions are represented implicitly through the aid of a single vertex which is the tip of an infinite cone. The cones are similar to halfspaces in a CSG representation; however, unlike CSG, the representation of an object with the vertices is unique. Additionally, vertex representations deal with scalar fields and not solids. Algorithms are given for generating vertex representation models for primitive solids, performing affine transformations, set-theoretic operations, and displaying vertex representation models. The algorithms assume that the vertices are stored in a list although they could also be stored using other representations (e.g., a point variant of a quadtree). The contribution of the work lies, in part, in the generality of the solutions obtained through the use of recursion to construct the representation in higher dimensions, as well as performing the operations on it. This is largely a result of the switch of the primitive unit to being a one-dimensional vertex list rather than a two-dimensional vertex list which was the original formulation of the representation. The vertex representation models the same objects that are obtained through use of methods such as an array of voxels or octrees (i.e., objects with orthogonal faces). Its advantage is that it requires less space and unlike octrees its space requirements are not sensitive to translation. Moreover, it enables increasing the qualit

Fast Polygonization of Variational Implicit Surfaces

This article presents a simple hierarchical adaptation of the Marching Cubes algorithm for polygonizing variational implicit surfaces used in modelling and reconstruction applications. The technique relies on placing the normal and boundary constraint points respecting a pseudo-Euclidean distance metrics. This procedure makes it possible to quickly prune the space and minimize the number of costly function evaluations and thus converge rapidly to the surface. Timings show that this technique tends to perform faster than Bloomenthal’s continuation polygonizer [5]. 1

Laplacian face blending

Designing realistic tridimensional facial models is a challenging task, not only due to the effort and artistic abilities required but also because human visual perception is very tuned to the processing of facial features. For this reason, rather than creating face models from scratch, artists usually start from a scanned model of a real person. In this work, we present a novel method for blending human faces in order to create a new one. In a nutshell, our proposal uses Laplacian smoothing to segregate layers of details from one or more faces, which are then integrated into a base face with the help of an interactive and visual editor. In particular, our method supports blending multiple faces and multiple sub-regions in those faces. Since our approach is intuitive and relatively easy to implement, it can be integrated into artistic pipelines aiming at designing human face models from preexisting ones.Comp Graphics & Visualisatio

3D free-form modeling with variational surfaces

We describe a free-form stroke-based modeling system where objects are primarily represented by means of variational surfaces. Although similar systems have been described in recent years, our approach achieves both a good performance and reduced surface leak problems by employing a coarse mesh as support for constraint points. The prototype implements an adequate set of modeling operations, “undo” and “redo” facilities and a clean interface capable of resolving ambiguities by means of suggestion thumbnails