三维地图线要素注记自动放置算法研究

发布时间：2018-05-14 05:33

本文选题：三维地图 + 线要素注记　；参考：《南京大学》2017年硕士论文

【摘要】：地图注记作为地图的一个重要组成部分可以帮助使用者快速地建立图上要素与现实地理对象之间的联系,并为使用者提供在现实世界无法直接获取的信息,例如标注地块的面积、道路的长度等信息。地图注记的自动放置是地图学领域的一个重要研究问题。地图注记自动放置算法在为每一个地理要素确定其文字注记在地图上的位置时,需要确保注记与所标注地理要素之间的关联性易于辨识,并避免地图注记之间的重叠。三维地图的注记放置问题与传统的二维地图相比,面临更为复杂的情况。在三维地图中,地形的起伏、各类三维人工构筑物会对注记文字产生遮挡。视点在三维空间内的任意变换,会改变注记间的透视关系,影响其在屏幕空间上的相对位置,因而难以在预处理阶段计算出注记间潜在的冲突关系。此外,对于三维线状要素,注记文字必须保持沿线分布,但线要素的走向改变会引起注记文字朝向的变化,进而影响注记的可读性。线要素在三维空间的深度延展,导致视点与线要素的不同部位之间具有不同的距离,这对注记参考线不同部位的细节层次提出了有差异的要求。本研究在国家自然科学基金面上项目"典型二维矢量地图要素在三维地形表面的贴合渲染算法研究"(41371365)的支持下提出了一种三维交互地图中线要素文字注记的放置算法。既参考传统二维地图注记的放置策略,也考虑三维地图场景的特殊性,制定了三维地图线要素注记的放置规则。进一步地,实现了一个快速的三维地图线要素文字注记放置的算法框架。在预处理阶段,通过内插高程点将注记参考线贴合到起伏的地形表面,并生成静态的注记参考线层次树结构。在场景渲染过程中,借助于该注记参考线层次树结构,动态生成视点相关的注记参考线。然后对其执行视锥体裁剪,基于阴影图算法实现遮挡裁剪,解决地形与建筑物的遮挡问题,进行单调性分割等。在去除过短的注记参考线段之后,将其投影至屏幕空间,在屏幕空间上使用一个无回溯的图着色算法处理注记之间的冲突问题。实验结果表明本研究提出的三维地图线要素注记自动放置算法生成的注记放置方案能够适应不同视距以及观察角度的变化,注记朝向可以很好反映出线要素的走向,当注记参考线过度曲折时,可以自动将注记参考线分割为多段处理,有效解决了地形对注记的遮挡以及注记之间的冲突问题,并能够满足三维地图应用程序的实时交互需求。
[Abstract]:As an important part of a map, map notation can help users quickly establish links between the elements of a map and real geographic objects and provide users with information that is not directly accessible in the real world. Such as marking the land area, road length and other information. The automatic placement of map notes is an important research problem in the field of cartography. When determining the location of each geographical element on the map, the automatic placement algorithm needs to ensure that the correlation between the annotated and marked geographical elements is easy to identify, and to avoid the overlap between the annotated map. Compared with the traditional two-dimensional map, the problem of three-dimensional map is more complicated. In three-dimensional maps, the ups and downs of the terrain, all kinds of three-dimensional artificial structures will block the annotated text. Any transformation of viewpoint in 3D space will change the perspective relationship between notes and affect the relative position in screen space, so it is difficult to calculate the potential conflict relationship between notes in the preprocessing stage. In addition, for three dimensional linear elements, note characters must be distributed along the line, but the change of line elements will cause changes in the direction of the notes, and then affect the readability of the notes. The depth extension of line elements in three dimensional space leads to different distance between viewpoint and different parts of line elements, which puts forward different requirements for the details of different parts of the reference line. Supported by the National Natural Science Foundation of China (NSFC) project, "A study on the matching rendering algorithm of typical 2-D Vector Map elements on 3D terrain Surface", this paper presents an algorithm for placing the text of line elements in 3D interactive maps. By referring to the placement strategy of the traditional two-dimensional map notation and considering the particularity of the 3D map scene, the rules of placing the elements of the 3D map line are established. Furthermore, a fast algorithm framework for text annotation and placement of line elements in three-dimensional maps is implemented. In the preprocessing stage, the reference line is fitted to the topographic surface by interpolation of elevation points, and a static hierarchical tree structure of the reference line is generated. In the process of scene rendering, the reference line is dynamically generated with the help of the hierarchical tree structure of the note reference line. Then the visual cone clipping is performed, the shading is realized based on the shadow map algorithm, the occlusion problem between the terrain and the building is solved, and the monotonic segmentation is carried out. After removing the short reference line segment, it is projected to the screen space, and a graph coloring algorithm without backtracking is used to deal with the conflict between the notes. The experimental results show that the new method can adapt to the change of different visual distance and observation angle, and the direction of note can well reflect the trend of line element. When the note reference line is too tortuous, the reference line can be automatically divided into multi-section processing, which effectively solves the problem of terrain occlusion and conflict between notes, and can meet the real-time interactive requirements of 3D map applications.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P208;P283

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