Figure 1: Left: simplified mesh of 15K triangles. Middle: an octree is built around this mesh to adaptively sample and store the normal field of the high resolution version of the mesh. Right: the simplified mesh is normal mapped via a special GPU traversal of the octree cells encoded in a 2D texture. The operation does not requires 2D parametrization of the mesh. AbstractBecause of their geometric complexity, high resolution 3D models, either designed in high-end modeling packages or acquired with range scanning devices, cannot be directly used in applications that require rendering at interactive framerates. One clever method to overcome this limitation is to perform an appearance preserving geometry simplification, by replacing the original model with a low resolution mesh equipped with high resolution normal maps. This process visually preserves small scale features from the initial geometry, while only requiring a reduced set of polygons. However, this conversion usually relies on some kind of global or piecewise parameterization, combined with the generation of a texture atlas, a process that is computationally expensive and requires precise user supervision. In this paper, we propose an alternative method in which the normal field of a high resolution model is adaptively sampled and encoded in an octree-based data structure, that we call appearance preserving octree-texture (APO). Our main contributions are: a normal-driven octree generation, a compact encoding and an efficient look-up algorithm. Our method is efficient, totally automatic, and avoids the expensive creation of a parameterization with its corresponding texture atlas.

Predicting the soil-to-plant transfer of metals in the context of global warming has become a major issue for food safety. It requires a better understanding of how the temperature alters the bioavailability of metals in cultivated soils. This study focuses on one agricultural soil contaminated by Cd, Zn and Pb. DGT measurements were performed at 10, 20 and 30 °C to assess how the bioavailability of metals was affected by a rise in soil temperature. A lettuce crop was cultivated in the same conditions to determine if the soil-to-plant transfer of metals increased with a rise in soil temperature. A gradual decline in Cd and Zn bioavailability was observed from 10 to 30 °C, which was attributed to more intense complexation of metals in the pore water at higher temperatures. Together with its aromaticity, the affinity of dissolved organic matter (DOM) for metals was indeed suspected to increase with soil temperature. One main output of the present work is a model which satisfactorily explains the thermal-induced changes in the characteristics of DOM reported in Cornu et al. (Geoderma 162:65-70, 2011) by assuming that the mineralization of initial aliphatic compounds followed a first-order reaction, increased with soil temperature according to the Arrhenius law, and due to a priming effect, led to the appearance of aromatic molecules. The soil-to-plant transfer of Cd and Zn was promoted at higher soil temperatures despite a parallel decrease in Cd and Zn bioavailability. This suggests that plant processes affect the soil-to-plant transfer of Cd and Zn the most when the soil temperature rises.

Figure 1: Architecture of the APO web 3D viewer. The client, a web browser applet, progressively downloads the APO texture, while rendering the coarse model with previously downloaded details. The normal field is encoded in the APO which is an Appearance Preserving Octree-texture. Normal mapping on the simplified mesh is done on the client side by the fragment shader. AbstractThe development of shape repositories and 3D databases rises the need of online visualization of 3D objects. The main issue with the remote visualization of large meshes is the transfer latency of the geometric information. The remote viewer requires the transfer of all polygons before allowing object's manipulation. To avoid this latency problem, an approach is to send several levels of details of the same object so that lighter versions can be displayed sooner and replaced with more detailed version later on. This strategy requires more bandwidth, implies abruptly changes in object aspect as the geometry refines as well as a non negligible precomputing time.Since the appearance of a 3D model is more influenced by its normal field than its geometry, we propose a framework in which the object's LOD is replaced with a single simplified mesh with a LOD of appearance. By using Appearance Preserving Octree-Textures (APO), this appearance LOD is encoded in a unique texture, and the details are progressively downloaded when they are needed. Our APO-based framework achieves a nearly immediate object rendering while details are transmitted and smoothly added to the texture. Scenes keep a low geometry complexity while being displayed at interactive framerate with a maximum of visual details, leading to a better visual quality over bandwith ratio than pure geometric LOD schemes. Our implementation is platform independent, as it uses JOGL and runs on a simple web browser. Furthermore the framework doesn't require processing on the server side during the client rendering. *

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