为了画图方便,轴测投影中常用四心扁圆代替椭圆。目前常用的几种画四心扁圆方法中,有的较准确,但作图较烦;有的虽很简便,但误差较大;虽然也有些方法既简便又精确,但只能适用于某一种特定的轴测投影。至于不同的轴测投影(如正等测与正二测)四心扁圆的画法完全不同,制图者颇感不便。对于不常用的椭圆,如不平行于坐标面的圆的轴测投影、斜等测、正三测等等,还没有用四心扁圆代替的方法。 In order to facilitate the drawing, Axis projection commonly used four oblate instead oval. At present, there are several methods commonly used to draw four-hearted oblate circles, some of which are more accurate but more annoying to draw. Some of them are very simple, but the errors are relatively large. Although some methods are simple and accurate, they can only be applied to some A special axonometric projection. As for the different axonometric projection (such as being equal and positive two measurements) four heart oblate drawing completely different, the plotter quite inconvenient. For less commonly used oval, such as the axis of projection is not parallel to the coordinate plane projection, oblique measurement, is the third test and so on, there is no method to replace the four heart oblate.