VLISP函数确定地质灾害点与震裂迹线的距离

Solution for distance between positions of geohazard and traces of seismogenic fault by VLISP functions

在强震区地质灾害发育因素评价中,离发震断裂的远近与地震波传播、衰减等响应紧密相关,是不可忽视的变量.灾害点的数据量很大时,对其指标提取工作,须借助于图形软件的有关功能.除主流的GIS方式外,着重研究了在Auto CAD系统中求取各地质灾害点与断层距离指标的命令.将输入的一系列点与各条曲线进行两重循环,利用求曲线上最近点的vlax-curve-getClosestPointTo函数,逐点逐线求解.选用汶川地震灾害实例进行测试,对于点数上万及线段节点数百的问题规模,用时不超10 s,表明CAD系统也是提取距离指标的有效辅助手段;同时该实例也展示了断层距离对震害区地质灾害影响的显著性.因此,对此类实际而又细碎的基础问题,需重视各种软件系统求解方法的研究.

Distances, the geohazards far away from the seismogenic fault, related to propagation and attenuation of the seismic wave are essential variables taken into account in the evaluation of factors raised the geohazards, which can be obtained with the aid of related functions of some graphics softwares. Besides the prevalent GIS software, a custom command in the Auto CAD system was developed, which was used to solve the problem of distances between positions, where geohazards have arisen, and faults. The idea governing this approach is as follows, find the closest point on the traces of fault one by one to each geohazard point by the visual LISP function （vlax - curve - get Closest Point to curve -obj givenPnt）, and then, output each distance from input point to nearest point obtained on the fault into a result file . According to the test to such custom command suing the cases of geohazards in influence area of ＂5. 12＂ Wenchuan earthquake, It was taken only about 10 seconds to solve the distances between 10 thousands of geohazards and the traces of fault, on which have hundreds node. So this test proved such a method to be very efficient in the CAD software, as well. At the same time, these cases also showed the significant influence of the fault distance on geohazard associated with earthquakes. Therefore, with regard to such kinds of the down - to - earth routine, although fundamental and tiny, it is necessary to pay attention to research the methods to handle it in various systems of computer graphics software.