Seasonally dry tropical forests are distributed across Latin America and the Caribbean and are highly threatened, with less than 10% of their original extent remaining in many countries. Using 835 ...inventories covering 4660 species of woody plants, we show marked floristic turnover among inventories and regions, which may be higher than in other neotropical biomes, such as savanna. Such high floristic turnover indicates that numerous conservation areas across many countries will be needed to protect the full diversity of tropical dry forests. Our results provide a scientific framework within which national decision-makers can contextuaiize the floristic significance of their dry forest at a regional and continental scale.
Dense optical flow is a crucial visual cue for obstacle avoidance and motion control for robotic systems functioning in complex unstructured environments. In order to compute image motion for modern ...highly dynamic robots, it is necessary to use high speed vision systems. To perceive small and thin objects such as tree branches, fence poles, and other similar objects, high resolution vision systems must be used. The data stream from a high-resolution, high-speed vision system will saturate the onboard data bus and overload the onboard processor of almost all existing robotic systems. To implement such a vision system, we believe it is necessary to process the data in situ at the camera using dedicated processing hardware, a vision processing paradigm that we term rapid embedded vision (REV) systems. Even then, the task of processing multiple hundred hertz of dense high-resolution images is not possible using classical algorithms and classical computing hardware. A new processing paradigm that actively exploits the high frame rate of the image sequences, and high performance computing hardware such as GPU or FPGA must be employed. This letter proposes a filtering algorithm for the computation of dense optical flow fields in real time. The filter is designed as a pyramidal structure of update and propagation loops, where an optical flow state is constantly refined with new image data from the camera. The computational properties of the proposed algorithm makes it well suited for implementation in GPU and FPGA systems. We present results from a GPU implementation achieving frame rates in the order of 800 Hz at VGA resolution. Experimental validation and comparison is provided for both synthetic and real life high speed video sequences at frame rates of 300 Hz and 1016 × 544 pixel resolution.
This letter introduces the "spherepix" data structure for efficient implementation of low-level image processing operations on spherical images. Efficient implementation of low-level image processing ...depends heavily on separability of the convolution kernels that form the fundamental building blocks of most algorithms. Due to the curvature of the sphere, it is not possible to place an orthogonal grid pixelation globally on its surface, making direct application of classical separable kernel convolutions impossible. In the spherepix data structure, we propose an alternative approach consisting of a collection of overlapping (near orthogonal) grid patches covering the sphere's surface. Close to the boundaries of patches, we introduce data interpolation between patch grids to ensure information flow between grid patches. After each image processing subroutine, we reconcile data in the overlapping regions to homogenize the global data representation. We claim that the additional computational cost of data interpolation and data reconciliation is easily compensated by the computational saving and algorithmic simplicity of applying existing image processing subroutines in the grid patches. The approach is demonstrated by implementing a SIFT feature point algorithm in spherepix coordinates and comparing precision, recall, and computational cost of the proposed approach to documented modifications of the SIFT algorithm specifically developed for implementation on spherical images.
Real-time Structure Flow Adarve, Juan David; Mahony, Robert
arXiv.org,
06/2024
Paper, Journal Article
Odprti dostop
This article introduces the structure flow field; a flow field that can provide high-speed robo-centric motion information for motion control of highly dynamic robotic devices and autonomous ...vehicles. Structure flow is the angular 3D velocity of the scene at a given pixel. We show that structure flow posses an elegant evolution model in the form of a Partial Differential Equation (PDE) that enables us to create dense flow predictions forward in time. We exploit this structure to design a predictor-update algorithm to compute structure flow in real time using image and depth measurements. The prediction stage takes the previous estimate of the structure flow and propagates it forward in time using a numerical implementation of the structure flow PDE. The predicted flow is then updated using new image and depth data. The algorithm runs up to 600 Hz on a Desktop GPU machine for 512x512 images with flow values up to 8 pixels. We provide ground truth validation on high-speed synthetic image sequences as well as results on real-life video on driving scenarios.
Vision offers important sensor cues to modern robotic platforms. Applications such as control of aerial vehicles, visual servoing, simultaneous localization and mapping, navigation and more recently, ...learning, are examples where visual information is fundamental to accomplish tasks. However, the use of computer vision algorithms carries the computational cost of extracting useful information from the stream of raw pixel data. The most sophisticated algorithms use complex mathematical formulations leading typically to computationally expensive, and consequently, slow implementations. Even with modern computing resources, high-speed and high-resolution video feed can only be used for basic image processing operations. For a vision algorithm to be integrated on a robotic system, the output of the algorithm should be provided in real time, that is, at least at the same frequency as the control logic of the robot. With robotic vehicles becoming more dynamic and ubiquitous, this places higher requirements to the vision processing pipeline. This thesis addresses the problem of estimating dense visual flow information in real time. The contributions of this work are threefold. First, it introduces a new filtering algorithm for the estimation of dense optical flow at frame rates as fast as 800 Hz for 640x480 image resolution. The algorithm follows a update-prediction architecture to estimate dense optical flow fields incrementally over time. A fundamental component of the algorithm is the modeling of the spatio-temporal evolution of the optical flow field by means of partial differential equations. Numerical predictors can implement such PDEs to propagate current estimation of flow forward in time. Experimental validation of the algorithm is provided using high-speed ground truth image dataset as well as real-life video data at 300 Hz. The second contribution is a new type of visual flow named structure flow. Mathematically, structure flow is the three-dimensional scene flow scaled by the inverse depth at each pixel in the image. Intuitively, it is the complete velocity field associated with image motion, including both optical flow and scale-change or apparent divergence of the image. Analogously to optic flow, structure flow provides a robotic vehicle with perception of the motion of the environment as seen by the camera. However, structure flow encodes the full 3D image motion of the scene whereas optic flow only encodes the component on the image plane. An algorithm to estimate structure flow from image and depth measurements is proposed based on the same filtering idea used to estimate optical flow. The final contribution is the spherepix data structure for processing spherical images. This data structure is the numerical back-end used for the real-time implementation of the structure flow filter. It consists of a set of overlapping patches covering the surface of the sphere. Each individual patch approximately holds properties such as orthogonality and equidistance of points, thus allowing efficient implementations of low-level classical 2D convolution based image processing routines such as Gaussian filters and numerical derivatives. These algorithms are implemented on GPU hardware and can be integrated to future Robotic Embedded Vision systems to provide fast visual information to robotic vehicles.
The study of plant dispersal systems allows to go in depth in aspects that define the regeneration of forests, being essential to understand not only the population dynamics of plants but also the ...ecological relationships that emerge within ecosystems. In Colombia there is not a broad scale study showing the patterns of frequency and abundance of dispersal systems in different geographical regions (Amazonian, Andean, Caribbean, Upper Magdalena, Middle Magdalena, Orinoco, Pacific). Based on information of the identity and abundance of plants found in 101 vegetation plots of 1-ha, we explored the differences and associations in the frequency and abundance of dispersal systems between geographic regions. Additionally, we explored the importance value of families and genera per dispersal system, and the association between genera and geographic regions. The results show that environmental factors would be more important than the biogeographic history of the region in determining patterns of dispersal systems, reinforcing the importance of seed dispersal mediated by animals in tropical forests of different biogeographic regions.
El estudio de los sistemas de dispersión de las plantas permite entender la regeneración de los bosques, la dinámica poblacional de las especies vegetales y las relaciones ecológicas que emergen ...dentro de los ecosistemas. En el presente estudio se analizaron los patrones de sistemas de dispersión de semillas para Colombia, en relación con las regiones geográficas Amazónica, Andina, Caribe, Magdalena Alto, Magdalena Medio, Orinoquía y Pacífica. A partir de la información sobre la identidad y abundancia de plantas encontradas en 101 parcelas de vegetación de 1-ha, se exploraron los cambios en la frecuencia relativa y abundancia relativa de sistemas de dispersión entre las regiones geográficas. Adicionalmente, se determinaron las afinidades florísticas entre las regiones, así como
Perception is a key component for any robotic system. In this paper we present a method to construct occupancy grids by fusing sensory information using Linear Opinion Pools. We used lidar sensors ...and a stereo-vision system mounted on a vehicle to make the experiments. To perform the validation, we compared the proposed method with the fusion method previously used in the Bayesian Occupancy Filter framework, using real data taken from highway and urban scenarios. The results show that our method is better at dealing with conflicting information coming from the sensors. We propose an implementation on parallel hardware which allows real-time execution.
The ecosystems of Valle del Cauca have been transformed to a landscape with few and small fragments of forest. This study measured the mortality and recruitment rates, changes in structure, ...composition, and biomass storage of the vegetation in a one-hectare permanent plot in the El VÃnculo Regional Natural Park, Valle del Cauca, in 2009 and 2011. One thousand, seven hundred sixty-eight stems with DAP ⥠5 cm were registered, which increased to 1811 stems in 2011, comprising 52 species and 25 families. Fabaceae and Rutaceae were the dominant families. The species with highest IVI, basal area, and biomass contribution were Eugenia procera, Amyris pinnata, Pithecellobium lanceolatum, Guapira sp. and Guazuma ulmifolia. The annual mortality rate (Tm= 4,84%) was due to stem death of heliophilous species. The annual recruitment rate (Tr= 6,94%) showed the success in dispersal and establishment of animal-dispersed species. The tendency of the vegetation was to increase basal area and biomass. We conclude that the forest is in an early successional stage, shows no disturbance, and is a reservoir representative of the diversity of tropical dry forest.
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