angle between -axis and -axis angle between -axis and -axis. The angles can be chosen so that The foreshortenings: Only for suitable choices of angles and foreshortenings does one get undistorted images. The next diagram shows the images of the unit cube for various angles and foreshortenings and gives some hints for how to make these personal choices. In order to keep the drawing simple, one should choose simple foreshortenings, for example or . If two foreshortenings are equal, the projection is called dimetric. If the three foreshortenings are equal, the projection is called isometric. If all foreshortenings are different, the projection is called trimetric. The parameters in the diagram at right (e.g. of the house drawn on graph paper) are: Hence it is a dimetric axonometry. The image plane is parallel to the y-z-plane and any planar figure parallel to the y-z-plane appears in its true shape. Special axonometries Engineer projection In this case the foreshortenings are: (dimetric axonometry) and the angles between the axes are: These angles are marked on many German set squares. Advantages of an engineer projection: simple foreshortenings, a uniformly scaled orthographic projection with scaling factor 1.06, the contour of a sphere is a circle (in general, an ellipse) . For more details: see :de:Axonometrie. Cavalier perspective, cabinet perspective image plane parallel to y-z-plane. In the literature the terms "cavalier perspective" and "cabinet perspective" are not uniformly defined. The above definition is the most general one. Often, further restrictions are applied. For example: cabinet perspective: additionally choose (oblique) and (dimetric), cavalier perspective: additionally choose (oblique) and (isometric). Birds eye view, military projection image plane parallel to x-y-plane. military projection: additionally choose (isometric). Such axonometries are often used for city maps, in order to keep horizontal figures undistorted. Isometric axonometry (Not to be confused with an isometry between metric spaces.) For an isometric axonometry all foreshortenings are equal. The angles can be chosen arbitrarily, but a common choice is . For the standard isometry or just isometry one chooses: (all axes undistorted) The advantage of a standard isometry: the coordinates can be taken unchanged, the image is a scaled orthographic projection with scale factor . Hence the image has a good impression and the contour of a sphere is a circle. Some computer graphic systems (for example, xfig) provide a suitable raster (see diagram) as support. In order to prevent scaling, one can choose the unhandy