贝塞尔曲线在虚拟森林景观单树几何模型构建中的应用

虚拟景观模型的生成,需要对实际景观进行抽象和简化。树几何模型和数字高程模型(DEM)是构成虚拟森林景观的两大要素。而树几何模型的构建又是林业GIS三维可视化的基础。在树几何建模中,树干及树枝形状的可视化表达具有突出意义。由于实际树种的复杂性,在计算机中建树模型,通常采用基于过程建模的方式,而这将面临用户如何对模型进行交互式控制的问题：参数太少,不足以描述树形态特征,而参数太多,则模型难以生成和理解。为了解决这个问题,我们引进贝塞尔(Bezier)曲线这种基于控制点的自由曲线来描述树木中的树干以及树枝形状,利用对曲线控制点的变动来控制曲线的形状,进而生成形态各异的树形状,对此,我们基于ActiveX技术生成Bezier曲线控件。结果表明,该方法能够表示多种形状的树干与树枝,具有操作简捷、计算速度快,可视化效果良好的优点。

Applying the Bezier Curve in Creating Tree Geometric Model on Virtual Forest

Digital landscape models require abstraction and simplification for realistic landscape.Tree geometricmodel and DEM are two elements in virtual forest.The tree geometric model is very important to forest GIS.Inthe process of model creation,the shape of trunk and branch have outstanding meanings.Because of theircomplexity,plant models used in computer graphics are usually created with procedural methods.A difficultproblem is the interactive control of these models:a small number of parameters is insufficient to specify plantcharacteristics,while a great number of parameters are tedious to manipulate and difficult to comprehend.Asthe shape of an actual tree is diverse,it is impossible to represent all kinds of trees in a special single curve.Toaddress this problem,the Bezier curve which is based on control points is introduced to depict the shape oftrunk and branch.And a OCX control is made to draw the Bezier curve,the result shows the manifold shape oftrunk and branch can be depicted by this method.It has many advantages such as conveniences and celeritywith good visualization effect.