Research On Interactive Tree Modeling Method In Virtual Reality

Tree models play a significant role in the construction of virtual natural scenes.Therefore,tree modeling methods for different application fields and requirements are also one of the widely-discussed directions of computer graphics and virtual plants.However,with existing methods,the modeling process is occupied with complex data collection and tedious parameter adjustment,and few studies have focused on the interactive experience of the tree modeling process.Conventional input devices(mouse,keyboard,stylus,etc.)have many limitations in expressing the complex three-dimensional branching structure of trees.In order to solve the above problems,combined with the characteristics of immersive interaction of virtual reality and the advantages of sketch-based modeling to express the branch structure,this paper proposes an immersive interactive tree modeling method in a VR environment,which allows to quickly generate tree models by sketching branches and trunks by the VR controller in 3D space,aiming to lower the difficulty of modeling and enhance the interaction and immersion in the designing process.The main contents are as follows:(1)A method of interactively generate models of tree branch and trunks.A sketch sampling and points optimization algorithm is presented to obtain the skeleton of the branch in 3D space.A bidirectional rayhit algorithm is introduced to determine the branch radius as real-time sketching.As generating geometry along the skeleton,a vector-projection method is applied to fix the branch polygon twisting.(2)A mesh deformation algorithm of branch models.Signed Distance Function and Gaussian Distance Falloff Function are applied to deform the mesh to simulate the smooth transition at the junction of branches and trunks.Based on the inverse square law,raise or hollow a part of branch mesh to simulate the uneven surface of a real branch.To meet the requirements of real-time interaction,GPU parallel computing is utilized to calculate vertex displacement.(3)A method of twigs generation and realistic simulation of tree canopy.A method of using oriented bounding boxes to express the shape of branches and trunks is proposed,and twigs are generated based on Perlin noise and the parent branch direction.Leaves,in the form of textured quad,are distributed on twigs following leaf arrangement rules.The interpolated canopy spherical normal is used to enhance the realistic shading effect.(4)An immersive and interactive tree modeling system.A user interface for VR is designed and implemented,allowing users to use HTC Vive controllers to sketch and deform branches in a virtual environment to interactively generate tree models.The experimental results show that the tree modeling method proposed in this paper can quickly obtain a variety of tree models and meet the requirements of VR real-time interaction.Immersive and interactive tree modeling also provides a novel approach to quickly generate realistic tree models.