Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion

International audienceAt large scale, landscapes result from the combination of two major processes: tectonics which generate the main relief through crust uplift, and weather which accounts for erosion. This paper presents the first method in computer graphics that combines uplift and hydraulic erosion to generate visually plausible terrains. Given a user-painted uplift map, we generate a stream graph over the entire domain embedding elevation information and stream flow. Our approach relies on the stream power equation introduced in geology for hydraulic erosion. By combining crust uplift and stream power erosion we generate large realistic terrains at a low computational cost. Finally, we convert this graph into a digital elevation model by blending landform feature kernels whose parameters are derived from the information in the graph. Our method gives high-level control over the large scale dendritic structures of the resulting river networks, watersheds, and mountains ridges

The design-by-adaptation approach to universal access: learning from videogame technology

This paper proposes an alternative approach to the design of universally accessible interfaces to that provided by formal design frameworks applied ab initio to the development of new software. This approach, design-byadaptation, involves the transfer of interface technology and/or design principles from one application domain to another, in situations where the recipient domain is similar to the host domain in terms of modelled systems, tasks and users. Using the example of interaction in 3D virtual environments, the paper explores how principles underlying the design of videogame interfaces may be applied to a broad family of visualization and analysis software which handles geographical data (virtual geographic environments, or VGEs). One of the motivations behind the current study is that VGE technology lags some way behind videogame technology in the modelling of 3D environments, and has a less-developed track record in providing the variety of interaction methods needed to undertake varied tasks in 3D virtual worlds by users with varied levels of experience. The current analysis extracted a set of interaction principles from videogames which were used to devise a set of 3D task interfaces that have been implemented in a prototype VGE for formal evaluation

Unlimited object instancing in real-time

In this paper, we propose a novel approach to efficient rendering of an unlimited number of 3D objects in real-time. We present a rendering pipeline that is based on a new computer graphics programming paradigm implementing a holistic approach to the virtual scene definition. Using Signed Distance Functions (SDF) for a virtual scene representation, we managed to control the content and complexity of the virtual scene with the use of mathematical equations. In order to solve the limited hardware problem, especially the limited capacity of the GPU memory, we propose a scene element repository which extends the idea of the data based amplification. The content of the repository strongly depends on a 3D object visualization method. One of the most important requirements of the developed pipeline is the possibility to render 3D objects created by artists. In order to achieve that, the object visualization method uses Sparse Voxel Octree (SVO) ray casting. The developed rendering pipeline is fully compatible with the available SVO algorithms. We show how to avoid occlusion errors which can occur in the SDF and SVO integration single-pass rendering pipeline. Finally, in order to control the content and complexity of the virtual scenes in an unlimited way, we propose a collection of global operators applicable to the virtual scene distance function. Developed Unlimited Object Instancing rendering pipeline can be easily integrated with traditional visualization methods, e.g. the triangle rasterization. The only hardware requirement for our approach is the support for compute shaders or any GPGPU API

Perceptual Scale Expansion: An Efficient Angular Coding Strategy For Locomotor Space

Whereas most sensory information is coded on a logarithmic scale, linear expansion of a limited range may provide a more efficient coding for the angular variables important to precise motor control. In four experiments, we show that the perceived declination of gaze, like the perceived orientation of surfaces, is coded on a distorted scale. The distortion seems to arise from a nearly linear expansion of the angular range close to horizontal/straight ahead and is evident in explicit verbal and nonverbal measures (Experiments 1 and 2), as well as in implicit measures of perceived gaze direction (Experiment 4). The theory is advanced that this scale expansion (by a factor of about 1.5) may serve a functional goal of coding efficiency for angular perceptual variables. The scale expansion of perceived gaze declination is accompanied by a corresponding expansion of perceived optical slants in the same range (Experiments 3 and 4). These dual distortions can account for the explicit misperception of distance typically obtained by direct report and exocentric matching, while allowing for accurate spatial action to be understood as the result of calibration

Caractéristiques des marées dans le golfe du Tonkin

Le golfe du Tonkin, située dans la mer de l'Est/la mer de Chine du Sud, est une zone de fort intérêt écologique, touristique et économique. Améliorer notre connaissance de ses processus hydro-sédimentaires (transport de particules en suspension) est d'une grande importance. L'objectif scientifique de cette étude est de revoir les processus physiques dominants qui caractérisent la dynamique des marées dans le golfe du Tonkin en utilisant un modèle à haute résolution et la combinaison de toutes les données disponibles. Une attention particulière est donc accordée à un examen croisé du modèle, des marégraphes et de l'altimétrie en zone côtière, ainsi qu'à l'étalonnage du modèle dérivé d'un ensemble d'expériences de sensibilité aux paramètres. Le bilan d'énergie des marées du golfe (flux d'énergie et de dissipation) est ensuite analysé et ses propriétés de résonance sont évaluées et comparées avec des modèles idéalisés et les observations. Ensuite, la marée résiduelle eulérienne et lagrangienne est évaluée. Enfin, on montre que le mélange de marée ne suffit pas à expliquer les structures frontales observées et associées à des concentrations élevées de chlorophylle.The Gulf of Tonkin, situated in the Vietnam East Sea/South China Sea, is a zone of strong ecological, touristic and economic interest. Improving our knowledge of its hydro-sedimentary processes (transport of suspended particles) is of great importance. The scientific objective of this study is to revisit the dominant physical processes that characterize tidal dynamics in the Gulf of Tonkin using a high-resolution model and the combination of all available data. Particular attention is thus given to model-data cross-examination using tidal gauges and coastal satellite altimetry data and to model calibration derived from a set of sensitivity experiments to model parameters. The tidal energy budget of the gulf (energy flux and dissipation) is then analyzed and its resonance properties are evaluated and compared with idealized models and observations. Then, the tidal residual flow in both Eulerian and Lagrangian frameworks is evaluated. Finally, the problem of tidal frontogenesis is addressed showing that tidal mixing alone does not explain the observed summer frontal structures in chlorophyll concentrations

Towards a Neural Graphics Pipeline for Controllable Image Generation

In this paper, we leverage advances in neural networks towards forming a neural rendering for controllable image generation, and thereby bypassing the need for detailed modeling in conventional graphics pipeline. To this end, we present Neural Graphics Pipeline (NGP), a hybrid generative model that brings together neural and traditional image formation models. NGP decomposes the image into a set of interpretable appearance feature maps, uncovering direct control handles for controllable image generation. To form an image, NGP generates coarse 3D models that are fed into neural rendering modules to produce view-specific interpretable 2D maps, which are then composited into the final output image using a traditional image formation model. Our approach offers control over image generation by providing direct handles controlling illumination and camera parameters, in addition to control over shape and appearance variations. The key challenge is to learn these controls through unsupervised training that links generated coarse 3D models with unpaired real images via neural and traditional (e.g., Blinn- Phong) rendering functions, without establishing an explicit correspondence between them. We demonstrate the effectiveness of our approach on controllable image generation of single-object scenes. We evaluate our hybrid modeling framework, compare with neural-only generation methods (namely, DCGAN, LSGAN, WGAN-GP, VON, and SRNs), report improvement in FID scores against real images, and demonstrate that NGP supports direct controls common in traditional forward rendering. Code is available at http://geometry.cs.ucl.ac.uk/projects/2021/ngp.Comment: Eurographics 202

Simulation of all-scale atmospheric dynamics on unstructured meshes

The advance of massively parallel computing in the nineteen nineties and beyond encouraged finer grid intervals in numerical weather-prediction models. This has improved resolution of weather systems and enhanced the accuracy of forecasts, while setting the trend for development of unified all-scale atmospheric models. This paper first outlines the historical background to a wide range of numerical methods advanced in the process. Next, the trend is illustrated with a technical review of a versatile nonoscillatory forward-in-time finite-volume (NFTFV) approach, proven effective in simulations of atmospheric flows from small-scale dynamics to global circulations and climate. The outlined approach exploits the synergy of two specific ingredients: the MPDATA methods for the simulation of fluid flows based on the sign-preserving properties of upstream differencing; and the flexible finite-volume median-dual unstructured-mesh discretisation of the spatial differential operators comprising PDEs of atmospheric dynamics. The paper consolidates the concepts leading to a family of generalised nonhydrostatic NFTFV flow solvers that include soundproof PDEs of incompressible Boussinesq, anelastic and pseudo-incompressible systems, common in large-eddy simulation of small- and meso-scale dynamics, as well as all-scale compressible Euler equations. Such a framework naturally extends predictive skills of large-eddy simulation to the global atmosphere, providing a bottom-up alternative to the reverse approach pursued in the weather-prediction models. Theoretical considerations are substantiated by calculations attesting to the versatility and efficacy of the NFTFV approach. Some prospective developments are also discussed

Mars Science Helicopter Conceptual Design

Robotic planetary aerial vehicles increase the range of terrain that can be examined, compared to traditional landers and rovers, and have more near-surface capability than orbiters. Aerial mobility is a promising possibility for planetary exploration as it reduces the challenges that difficult obstacles pose to ground vehicles. The first use of a rotorcraft for a planetary mission will be in 2021, when the Mars Helicopter technology demonstrator will be deployed from the Mars 2020 rover. The Jet Propulsion Laboratory and NASA Ames Research Center are exploring possibilities for a Mars Science Helicopter, a second-generation Mars rotorcraft with the capability of conducting science investigations independently of a lander or rover (although this type of vehicle could also be used assist rovers or landers in future missions). This report describes the conceptual design of Mars Science Helicopters. The design process began with coaxial-helicopter and hexacopter configurations, with a payload in the range of two to three kilograms and an overall vehicle mass of approximately twenty kilograms. Initial estimates of weight and performance were based on the capabilities of the Mars Helicopter. Rotorcraft designs for Mars are constrained by the dimensions of the aeroshell for the trip to the planet, requiring attention to the aircraft packaging in order to maximize the rotor dimensions and hence overall performance potential. Aerodynamic performance optimization was conducted, particularly through airfoils designed specifically for the low Reynolds number and high Mach number inherent in operation on Mars. The final designs show a substantial capability for science operations on Mars: a 31 kg hexacopter that fits within a 2.5 m diameter aeroshell could carry a 5 kg payload for 10 min of hover time or over a range of 5 km