c#+绘制直线+橡皮筋效果，用于GIS的基本图形绘制，利于初学者学习-c#+ draw a straight line+ rubber band effect, the basic graphics for GIS mapping, which will help beginners to learn

实现GIS算法的基本功能，如绘画，矢量转栅格，橡皮筋技术，点选要素等功能。-Algorithm to achieve the basic functions of GIS, such as painting, Vector to raster, the rubber band technique, click on elements of other functions.

打开一个线文件和保存改变过的线文件，编辑线的属性和参数（调用mapgis函数）； 用橡皮筋的形式输入线，可以用F3撤销F4恢复-Open a line file and save the changed line files, edit the line attributes and parameters (call mapgis function) the form of input line with a rubber band, you can use F3 F4 withdrawa