Automatic Production of Highly-Precise Digital Elevation Models from Topographic Map Images and its Application

本项目对基于地形等高线图影像自动生成高精度数字高程模型（DEM）的试验系统进行了改进，使之更具有实用性。首先，我们将该系统应用于大量的真实的地形图，并检查了它所存在的问题。通过评价实验，我们发现在自动修复破损轮廓时存在以下问题：（1）修复可能失败;（2）无法检测修复失败的轮廓;（3）一旦连接修复后，无法改变破损轮廓的连接。针对这些问题，通过严格的恢复条件和抑制不可靠的相邻轮廓关系的产生，可以大大减少错误的发生。其次，我们发现了传统的由给定高程值的等高线生成DEM的插值方法存在的问题，提出了一种新的基于单调函数的插值方法。该方法具有以下特点：（1）可以生成高精度的DEM ;（2）不会产生像样条插值等方法经常产生的不必要的振动;（3）可以生成更合适的DEM曲面。我们还研究了基于正则化方法的Grimson方法，因为这类方法还没有得到很好的研究。第三，我们做了一个改进，使系统的用户友好的使用图形用户界面：例如，我们实现了交互式的恢复破碎的轮廓，利用人类模式识别的优秀功能。

In this project we made many improvements on the pilot system that can automatically produce a highly-precise digital elevation model (DEM) from images of topographic contour map, in order to make it more practicable. First, we applied the system to a lot of real topographic maps and examined the problems that it has. From the evaluation experiments, we found the following problems in automatic restoration of broken contours : (1) it may fail in restoration ; (2) it cannot detect contours with failed restoration ; (3) it cannot change connection of broken contours once they are connected to restore. To these problems, we could considerably decrease the occurrence of error restorations by using the rigid conditions for restoration and suppressing the generation of unreliable neighboring-contours relationship. Second, we found the problems in the traditional interpolation methods producing a DEM from contours given elevation values, and we developed a new interpolation method using monotone-function. The method has the following features : (1) it can produce a highly-precise DEM ; (2) It does not yield unnecessary vibrations that the other methods like the spline interpolation may often do ; (3) It can generate more suitable surfaces of DEM.We also examined the Grimson's method based on the regularization method, because the methods of this type have not been well investigated. Third, we did an improvement to make the system user-friendly by using graphical user interface : for example, we implemented the interactive restoration of broken contours to utilize the excellent function of human pattern recognition.