Research On Techniques For Modeling And Visual Simulating Characteristic Behaviors Of Plant

The morphological shape of a plant is its external representation, which may result from mutual influence between its underlying physiological process and the environmental factors. To simulate vividly the plant in computer, obviously, not only accurate modeling and rendering external appearances of a plant but also modeling its dynamic behaviors which are faithful to its underlying physiological mechanics is needed. Just in this way, the shape and motions of a plant can be simulated faithfully in virtual space. On the other hand, the behaviors characteristics of a plant are the most basic way and direct channel for human's recognizing, analyzing and evaluating the plant. Therefore it is practical significance and broad application perspectives to reveal the mutual influence and relations between its internal heredity characteristics and the environment with visual experience and 3D human-machine interaction, by using techniques and methods in computer graphics and virtual reality to describe quantitatively and visually the behaviors characteristics of plant, and to develop relevant software and interactive platforms.There is a long history in modeling 3D shape of plant and simulating its motions, and remarkable achievements have been achieved thanks to many researchers'efforts. But due to the complexity and diversity of plant morphology, however, it is still a great challenge to reconstruct the shape of a plant and simulating its'behavior characteristics under different environments vividly. On the one hand, horticultural plant, especially melons and fruits, were less researched. Traditional methods for modeling plant shape generally focused on tree, in which the whole structure of tree was more important than the details on organs. Therefore, these methods would be not suitable for the modeling of horticultural plant that takes organs and individuals as basic unit. Secondly, although a various methods for modeling the morphology of crop organs have been proposed, these methods lack universality, and the realistic effects of the generated models need to be improved. In aspect of modeling deformation and motions of plant organs, some researchers have proposed various simulation methods, but they generally modeled at individual plant scale, not at organ scale. Moreover, they just simulated deformation of plant derived by extern forces, the automatically deformation and motions of a plant, such as curling of plant leaves under high temperature, are not considered yet. On the other hand, the climbing behavior which can be found commonly in horticultural plants has not been simulated from visualization perspective. Basing on the above analysis, this dissertation will focus on research the key techniques for modeling the 3D shape and simulating its typical behaviors of horticulture plants, by using theory and methodology from both computer graphics and physical modeling.This dissertation presents a methodology, firstly, for modeling and designing the 3D geometric shapes of main horticultural crops including cucumber, watermelon and tomato, by using techniques from computer-aid design (CAD), geometric modeling and 3D visualization; secondly, for creating parameterized geometric models of plant organs basing on existed agronomic models and knowledge rules. It is also a goal of this dissertation to develop physical models for simulating deformation and motions of plant. Lastly, the above techniques are integrated systematically to develop a visual platform for simulating typical behaviors of plants, and demonstrating vividly the natural life behaviors of main horticultural crops in virtual environment, at organic, individual and crops scales.Specifically, the main contributions and innovations of this dissertation can be listed as follows:1 Modeling accurate geometry of organs and interactive designing plant structure of horticultural cropsTo handle the diversity of species and irregularity of morphogenesis in plant, a B-splines curves-based method which using a skeleton description of organs shape and constructing the geometry of an organ from the skeleton was proposed. With this model users could create a wide range of crop organs with high realistic shape. This method aims to provide a common representation of irregular outlines of plant organs by utilizing the flexibility of B-splines curves. The principal control parameters of these geometric models were then extracted from existed agronomic models and knowledge rules. Delaunay triangulation was used to mesh irregular polygon in organs surface, such as lobed leaf surface. Furthermore, an adaptive subdivision scheme was used to smooth the generated mesh of a leaf blade. Basing on the geometric models of organs, an interface for designing crops structure interactively was developed, in which techniques such as organs templates and morphing were used to generate transitional shapes between two growth stages of an organ.2 Techniques for realistic rendering 3D plant modelsFor improving the appearance of the computer generated plant geometric models, several details description techniques were used in this dissertation. Texture mapping was used to leaf and fruit models, while process texture generation was introduced to cylinder-like organs such as caudex and petiole. Moreover, a method for generating plant hairs that cover many plant organs was proposed. This method employed Poisson-disk pattern to assign the distribution of hairs on the surface of each organ, while the density of hairs was adjusted based on the area of organ surface. This can avoid generating irregular pattern of hairs on irregular surface. Individual hairs were then mapped onto the organ surfaces according to the generated attachment points. Hair properties including length, radius, direction and density were specified and adjusted according to positional information of the organ surface, and the geometry of individual hair can be represented as curve or cylinder. This allows generating a wide range of hairs styles. Sample results showed that the proposed method can render realistic hairs in real-time, and can represent various styles of hairy plant effectively.3 Real-time simulating deformation of plant organsA method for modeling the deformation of plant organs based on mss-spring system was proposed, and parameterized methods for generating the 3D geometry and the spring model of plant organs were developed to satisfy the needs from interactive design. This could simplify the creation of mass-spring model. Results on several plant organs demonstrated that the proposed approach is applicable for simulating deformation of plant organs with realistic effects. Further, parameterized generation of geometric surface and physical model can be used in interactive simulation at real-time speed.4 Simulating curling and wilting of plant leavesTwo approximate physical kinetic models for simulating motions of plant leaves including curling and wilting were proposed in this dissertation. Firstly, a bi-layered mass-spring model consists of hierarchical spring was developed which was used to control the motions of leaves. Curling of a leaf blade was simulated by animating the spring tensions, while unfolding and wilting were simulated by animating the spring relaxation. With a suitably designed interface, animations can be obtained by manual interaction, which allowed for animating plant motions especially curling and wilting process of a leaf surface. Basing on the fact that the bi-layered mass-spring of a leaf model is difficult to be constructed, a venation skeleton-driven method for deforming plant leaves was proposed for this reason. Firstly, the leaf skeleton was used to generate a detail mesh for the leaf surface, and a venation skeleton was also generated interactively from the leaf skeleton. Each vein in the venation skeleton consisted of a segmented vertices string. Secondly each vertex in the leaf mesh was banded to the nearest vertex in the venation skeleton. We then deformed the venation skeleton by controlling the movement of each vertex in the venation skeleton by rotating it around a fixed vector. Finally the leaf mesh was mapped to the deformed venation skeleton, as such the deformation of the mesh followed the deformation of the venation skeleton. The proposed techniques have been applied to simulate leaf surface deformation resulted from biological responses of plant including wilting and curling.5 Modeling climbing characteristics and simulating climbing behavior of plantA model for simulating searching for support and growth of tendril was proposed, with this model, dynamic growth model of vine was developed. This model defined the special shape of the simulated vine according to its position in space with a considering if the tendrils on the vine have found support. By this way, the natural growth shape of a vine in gravity can be simulated. To detect collisions between organ and obstacle, organ and organ occur in the process of growth and drooping of the vine, techniques for detecting collisions between line and cylinder, line and bounding-box, cylinder and bounding-box were developed, and mechanics for avoiding collisions in real time were introduced simultaneously.