运用Morphing变换提取地性线算法研究

Geographic Line Extraction Algorithm Based on Morphing Transformation Techniques

  • 摘要: 由等高线获取山谷(脊)线对地形分析、坡度坡向计算和库区设计等应用具有重要的现实意义和非常高的生产价值。当前,面向等高线的地性线提取大多采用特征点连接法,其提取的地性线易与等高线发生空间逻辑冲突,在等高线弯曲形状较多变、较复杂的区域,所获取的山谷(脊)线存在与等高线弯曲特征不符且偏离较严重等问题。因此,依据地理学第一定律分析了等高线整体形态及局部形状特征,基于Morphing变换技术,提出了一种兼顾地性线两侧等高线形状特征,同时顾及山谷(脊)特征点位置约束的地性线提取新方法。首先,凭借各等高线的高程及其层次关系构建等高线树,并根据等高线上节点凹凸属性进行等高线弯曲分割,以高效准确地提取地形特征点;然后,以地形特征点为界构建其两侧等高线各节点之间的极优映射关系;最后,以地形特征点为约束,采用基于渐变移位距离值的Morphing变换提取地性线。实验结果表明,该方法能准确地提取出完整的与实际地形相吻合亦兼顾等高线整体形态与走势的地性线。

     

    Abstract:
    Objectives Obtaining valley (ridge) lines from contour data has important practical significance and high production value for terrain analysis, slope aspect calculation and reservoir area designing. In view of the fact that current contour-oriented geographic lines extraction mostly adopts feature point direct-connecting method, and the extracted geographic lines are prone to spatial logical conflicts with contour lines. Meantime, in areas where the contour lines are more curved and more complex, the extracted valley (ridge) line does not conform to the bending characteristics of contour lines, and even deviates dramatically in certain local areas.
    Methods Therefore, after overall shape and local shape characteristics of the contour line are analyzed sufficiently based on Tobler's first law, a novel methodology of extracting geographic lines from contour data based on Morphing transformation techniques is proposed, which takes the contour line on both sides of a valley (ridge) into consideration, as well as constraint of feature points’ location. First, a contour tree is constructed based on the elevation and hierarchical relationship of contours, and the contour curve segmentation is carried out according to the concave and convex attributes of nodes on the contour line. Then, the terrain feature points are extracted efficiently and accurately. Second, each contour line is split into two parts with the terrain feature points, whereafter, an optimal correspondence of the nodes on both parts of a contour line are computed. Third, with respect to the constraints of terrain feature points, the geographic lines are extracted by performing Morphing transformation with a gradient shifting distance value.
    Results The experimental results show that the methodology extracts complete geographic lines accurately, which are consistent with the actual terrain and take into account the overall shape and trend of contour lines.
    Conclusions The geographic lines extraction based on Morphing transformation techniques method can take into account the overall shape and trend of contour lines and unique shape at feature points to extract complete geographic lines consistent with the actual terrain, and it is robust. When the local terrain changes are complex, the contour shape is also complex. At this time, the allocation of Morphing transformation value for parameter t considering more factors will be involved, which is also the content to be further studied in the follow-up work.

     

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