Isometric Projections (正等轴测图)

Construction of isometric projection(正等轴测图的形成)

To produce an isometric projection, it is necessary to view an object such that its   principal edges are equally inclined to the viewer and hence are foreshortened equally.


Angle between isometric axes and coefficient of axial deformation (正等轴测图的轴间角和轴向伸缩系数)

 With an isometric projection, coordinate axes (O1X1-axis, O1Y1-axis and O1Z1-axis) are equally inclined to the P-plane and the isometric axes form angles of 120°from each other (see Fig. 5-2). It can be shown that, in this case, the coefficient of axial deformation for the three axes are p=q=r=0.82. However,as the utilization of such a ratio is quite complicated for drawing preparation, we often use a simplified ratio with p=q=r=1 and the drawing produced with such a simplified ratio is called an isometric drawing. It results in a view that is (1/0.82=)1.22 percent larger than that produced with the isometric projection, but conveys the same pictorial presentation of the object. Fig. 5-3 b and c show different views produced with isometric projections and isometric views, respectively.