Rafael J. Segura

A mobile 3D-GIS hybrid recommender system for tourism

The amount of touristic and travel information existing on the Internet is overwhelming. Recommender systems are typically used to filter irrelevant information and to provide personalized and relevant services to tourists. In this context, mobile devices are particularly useful because of their ubiquitous nature that turns them into an attractive platform for assisting on-the-move tourists to choose points of interest to visit according to their physical location. However, mobile devices also present several usability limitations that should be considered in order to provide information in a direct and intuitive way. In this paper, we present a novel mobile recommender system that brings together a hybrid recommendation engine and a mobile 3D GIS architecture. This system allows tourists to benefit from innovative features such as a 3D map-based interface and real-time location-sensitive recommendations. The details related to the design and implementation of the proposed solution are also presented, along with an empirical evaluation of user experience with the mobile application.

Navigating large terrains using commodity mobile devices

Abstract We describe a hybrid client–server technique for remote adaptive streaming and rendering of large terrains in resource-limited mobile devices. The technique has been designed to achieve an interactive rendering performance on a mobile device connected to a low-bandwidth wireless network. The rendering workload is split between the client and the server. The terrain area close to the viewer is rendered in real-time by the client. The terrain located far from the viewer is portrayed as view-dependent impostors, rendered by the server on demand. A prototype has been built and an exhaustive set of experiments covering several platforms, wireless networks and a wide range of viewer velocities has been conducted. Results show that the approach is feasible, effective and robust.

Technical section: Point in solid strategies

Testing whether a point is inside a solid is a basic operation in computer graphics. This document presents a variety of strategies for triangle meshes, a widely used data structure in computer graphics. We discuss some issues about the capabilities of each approach depending on the situation, taking into account memory and CPU usage. A practical comparison of the performance of several strategies is also presented, with implementation issues and time tables showing the performance of each algorithm. The tests highlight the strengths and weaknesses of each approach.

Collision detection between complex polyhedra

Collision detection (CD) between two objects is a complex task which demands spatial decomposition or bounding volume hierarchy in order to classify the features of the objects for a successful intersection test. Moreover, when the objects are complex and have concavities, holes, etc., the complexity of the decomposition increases and it is necessary to find a method which detects all special cases and degenerations. In this paper, we present a method for CD between complex polyhedra. We use a polyhedron representation based on simplicial coverings. With such as representation it is possible to model complex objects by using simpler objects (simplices), without any previous decomposition into convex pieces. The spatial decomposition so-called tetra-tree is utilized in order to classify the simplices of the covering, as well as a bounding volume hierarchy based on tetrahedra and spheres which allows us to drastically reduce the number of intersection tests between the features of both polyhedra. A time study has been performed to obtain a real time CD between two complex objects.

Fast and accurate evaluation of regularized Boolean operations on triangulated solids

In this paper we present a robust and accurate method for evaluating regularized Boolean operations on triangulated solids. It allows the exact evaluation of the regularized union, intersection, difference and symmetric difference simultaneously. Moreover, this approach is simpler than other methods, including those that provide an approximate evaluation or only a rendering of the result. It is based on a simple data structure and on the use of an octree which facilitates the division of the geometry into subsets for distribution among several threads, and accelerates the spatial queries needed during the process. This method is designed to be used in a multithreaded environment and it can also be implemented using an out-of-core approach. We also present some experimental results, and a comparison with other systems that also provide an exact evaluation of the Boolean operations.

An algorithm for determining intersection segment-polygon in 3D

Abstract In the fields related to geometric modelling, it is fundamental to count on robust. In this work we present a new algorithm for testing the intersection between a segment and a polygon in 3D space. This algorithm is robust and efficient, and it is the basis of most operations developed in geometric modelling. After, we will apply this algorithm to a classic problem in computer graphics: determining the hidden faces of a scene using the ray-casting algorithm. To solve the problem, an object-oriented approach will be used.

A new hierarchical triangle-based point-in-polygon data structure

The point-in-polygon or containment test is fundamental in computational geometry and is applied intensively in geographical information systems. When this test is repeated several times with the same polygon a data structure is necessary in order to reduce the linear time needed to obtain an inclusion result. In the literature different approaches, like grids or quadtrees, have been proposed for reducing the complexity of these algorithms. We propose a new data structure based on hierarchical subdivisions by means of tri-cones, which reduces the time necessary for this inclusion test. This data structure, named tri-tree, decomposes the whole space by means of tri-cones and classifies the edges of the polygon. For the inclusion test only the edges classified in one tri-cone are considered. The tri-tree has a set of properties which makes it specially suited to this aim, with a similar complexity to other data structures, but well suited to polygons which represent regions. We include a theoretical and practical study in which the new data structure is compared with classical ones, showing a significant improvement.

A scalable architecture for 3D map navigation on mobile devices

Mobile devices such as smart phones or tablets are rapidly increasing their graphics and networking capabilities. However, real-time visualization of 3D maps is still a challenging task to accomplish on such limited devices. In this paper, we describe the principles involved in the design and development of a scalable client–server architecture for delivering 3D maps over wireless networks to mobile devices. We have developed a hybrid adaptive streaming and rendering method that distributes the 3D map rendering task between the mobile clients and a remote server. This architecture provides support for efficient delivery of 3D contents to mobile clients according to their capabilities. As a proof of concept, we have implemented a prototype and carried out exhaustive experiments considering different scenarios and hundreds of concurrent connected clients. The analysis of the server workload and the mobile clients performance show that our architecture achieves a great scalability and performance even when using low-end hardware.

Rasterizing complex polygons without tessellations

Rasterization of polygons is a basic operation in computer graphics systems, representing the last and most time-consuming step in the visualization process. Therefore, the development of simple, efficient, and general polygon rasterization techniques is of prime interest. In this paper, we describe a new algorithm for this purpose, inspired on the ideas of the geometric modeling based on simplicial chains [Computer and Graphics 5 (1998) 611]. This algorithm is valid for any kind of polygon, is robust and extremely simple, and can be easily implemented in hard-ware. A similar approach can be used for the problem of polihedra voxelization in 3D.

A robust segment/triangle intersection algorithm for interference tests. Efficiency study

In this paper, a new algorithm for the intersection between a segment and a triangle in 3D is presented. This algorithm is suitable for interference tests between moving polyhedral solids, as is shown in the times study. In this situation it is necessary to determine whether the interference between triangles takes place (boolean test), and in some applications to determine the intersection point. When solids move certain changing information, such as the triangle normal, cannot be stored so the algorithms cannot take advantage of pre-calculations. A set of tests and a study of the computational cost of the new algorithm compared with classical algorithms are provided. These algorithms and studies can be used and extended by programmers in real applications.