A mixed pixel- and region-based approach for using airborne laser scanning data for individual tree crown delineation in Pinus radiata D. Don plantations

The aim of this study was to evaluate the use of high-resolution airborne laser scanner (ALS) data to detect and measure individual trees. We developed and tested a new mixed pixel- and region-based algorithm (using Definiens Developer 7.0) for locating individual tree positions and estimating their total heights. We computed a canopy height model (CHM) of pixel size 0.25 m from dense first-pulse point data (8 pulses m^?2) acquired with a small-footprint discrete-return lidar sensor. We validated the results of individual tree segmentation with accurate field measurements made in 37 plots of Monterey pine (Pinus radiata D. Don) distributed over an area of 36 km². Fieldwork consisted of labelling all of the trees in each plot and measuring their height and position, for posterior integration of the data from both sources (field and lidar). The proposed algorithm correctly detected and linked 59.8% of the trees in the 37 sample plots. We also manually located the trees by using FUSION software to visualize the raw lidar data cloud. However, because the latter method is extremely time-consuming, we only considered 10 randomly selected plots. Manual location correctly detected and linked 71.9% of the trees (in this subsample the algorithm correctly detected and measured 63.5% of the trees). The R² values for the linear model relating field- and lidar-measured heights of the linked trees located manually and with the automatic location algorithm were 0.90 and 0.88, respectively.     

Temporal scale and spatial resolution effects on Amazon forest fragmentation assessment in Rondônia

The Amazon has been under an intense deforestation process for the last 30 years, causing landscape fragmentation in many different regions and at distinct stages. The fragmentation process is commonly assessed by land‐use maps derived from satellite sensor data and analysed at a landscape context. The analysis of fragmentation depends on an adequate choice of spatial resolution of land‐use maps, and temporal scale in landscape dynamics studies. In this study, spatial–temporal resolution variation effects on fragmentation assessment were analysed in the Quatro Cachoeiras watershed, located at central Rondônia, Brazilian Amazon. Land‐use maps derived from 1984 to 2002 satellite sensor data at 2‐year intervals were used for landscape structure analysis on 12 samples randomly distributed along the watershed. In the spatial resolution variation analysis, landscape metrics obtained at 30 m resolution were compared with those obtained at coarser spatial resolutions. Effects of temporal scale variation were tested by comparison of landscape metrics calculated at 2‐, 4‐ and 6‐year intervals in the studied period. Results show that fragmentation stage influences sensitivity of landscape metrics for spatial resolution and at initial stages of fragmentation finer spatial resolution is required. Also, coarser resolutions up to 100 m could be used to assess landscape fragmentation at regions and the adequate time interval for landscape dynamics studies should be between 3 and 4 years.     

Ontology-based topological representation of remote-sensing images

This article proposes an ontology-based topological representation of remote-sensing images. Semantics, especially related to the topological relationships between the objects represented, are not explicit in remote-sensing images and this fact limits spatial analysis. Our aim is to provide an explicit ontological definition of the topological relations between objects in the image using the Quadtree data structure for spatial indexing. This structure is explicitly defined in an ontology allowing the automatic interpretation of the representations obtained, taking into account the topological relations and increasing the spatial analytical capabilities. This representation has been validated by a case study of semantic retrieval based on the normalized difference vegetation index (NDVI), taking into account the topological relations between NDVI regions in images. In the experiments, we compare the effectiveness of results from eight queries using four traditional supervised image classification algorithms and the proposal representation. The experimental results show the feasibility of the proposal, supporting the concept of the image retrieval process providing a semantic complement to remote-sensing images. The proposed representation contributes to incorporation of semantics into geographical data, especially to remote-sensing images, and it can be used to develop applications in the Geospatial Semantic Web.     

Model-driven approach to enterprise interoperability at the technical service level

Enterprise Interoperability is the ability of enterprises to interoperate in order to achieve their business goals. Although the purpose of enterprise interoperability is determined at the business level, the use of technical (IT) services to support business services implies that interoperability solutions at both the business and technical level should be aligned. This paper introduces and demonstrates the suitability of an approach based on model transformations to automate enterprise interoperability. We start by considering that a set of enterprises are willing to interoperate in the context of their individual goals. The interactions necessary for their cooperation are then properly captured in terms of a so-called choreography. Our approach allows a choreography to be mapped and transformed to an orchestration, which defines the operation of the actual technical services of the interoperating enterprises. The paper discusses the technical challenges of implementing the transformation, and illustrates our approach with two application scenarios.     

Adaptive Ray‐bundle Tracing with Memory Usage Prediction: Efficient Global Illumination in Large Scenes

This paper proposes an adaptive rendering technique for ray‐bundle tracing. Ray‐bundle tracing can be done by per‐pixel linked‐list construction on a GPU rasterization pipeline. This rasterization based approach offers significant benefits for the efficient generation of light maps (e.g., hardware acceleration, tessellation, and recycling of shaders used in real‐time graphics). However, it is inapplicable to large and complex scenes due to the limited capacity of the GPU memory because it requires a high‐resolution frame buffer and high‐capacity node buffer for the linked‐lists. In addition, memory overflow can potentially occur on the per‐pixel linked‐list since the memory usage of the lists is usually unknown before the rendering process. We introduce an adaptive tiling technique with memory usage prediction. Our method uses an appropriately tiled frame buffer, thus eliminating almost all of the overflow risks thanks to our adaptive tile subdivision scheme. Using this technique, we are able to render high‐quality light maps of large and complex scenes which cannot be computed using previous ray‐bundle based methods.     

Quad‐Mesh Generation and Processing: A Survey

Triangle meshes have been nearly ubiquitous in computer graphics, and a large body of data structures and geometry processing algorithms based on them has been developed in the literature. At the same time, quadrilateral meshes, especially semi‐regular ones, have advantages for many applications, and significant progress was made in quadrilateral mesh generation and processing during the last several years. In this survey we discuss the advantages and problems of techniques operating on quadrilateral meshes, including surface analysis and mesh quality, simplification, adaptive refinement, alignment with features, parametrisation and remeshing.     

An optimal expansion of Volterra models using independent Kautz bases for each kernel dimension

A new solution for the problem of selecting poles of the two-parameter Kautz functions in Volterra models is proposed. In general, a large number of parameters are required to represent the Volterra kernels, although this difficulty can be overcome by describing each kernel using a basis of orthonormal functions, such as the Kautz basis. This representation has a Wiener structure consisting of a linear dynamic generated by the orthonormal basis followed by a non-linear static mapping represented by the Volterra series. The resulting Wiener/Volterra model can be truncated into fewer terms if the Kautz functions are properly designed. The underlying problem is how to select the arbitrary complex poles that fully parametrize these functions. This problem has been approached in previous research by minimizing an upper bound for the error resulting from the truncation of the kernel expansion. The present paper goes even further in that each multidimensional kernel is decomposed into a set of independent Kautz bases, each of which is parametrized by an individual pair of conjugate Kautz poles intended to represent the dominant dynamic of the kernel along a particular dimension. An analytical solution for one of the Kautz parameters, valid for Volterra models of any order, is derived. A simulated example is presented to illustrate these theoretical results. The same approach is then used to model a real non-linear magnetic levitation system with oscillatory behaviour.     

Achievable performance limitations for SISO plants with pole location constraints

In this paper, performance limitations in the linear control of general linear discrete-time scalar systems are considered. The performance is measured with the 2-norm of an error function which, at the same time, ensures that the closed loop poles lie in a prescribed region. The deleterious effect of this constraint on a classical performance measurement is also quantified, in such a way, that the interplay between the size of the desired region and structural features of the plant is revealed.     

Correlation between impedance spectra of bulk ceramics and films with in-plane configuration

Strontium titanate is an interesting model electroceramics with grain boundary controlled properties. However, the relative role of grain boundaries may be significantly different in bulk ceramics and in films. Under oxidising conditions, impedance response of bulk ceramics can be described by series association of bulk and grain boundary contributions, which are distinguished based on major differences in relaxation frequencies. This allows de-convolution over relatively wide temperature ranges with standard impedance meters. In this case, one finds reasonably good correlations between microstructural effects and grain boundary behaviour. However, one finds major differences between those spectra and corresponding impedance spectra obtained for in-plane measurements of films. This may be partially accounted for by major increase in the equivalent thickness/area ratio as well as microstructural changes. In addition, the substrate may affect the results by significant leakage, and by stray capacitance effects exerted by a combination of substrate and experimental equipment.