The coordinate system in AutoCAD

The following will enter the graphics space provided by AutoCAD for the user. The main purpose is to use AutoCAD to draw graphics, so first of all to understand the Graphics object in the environment. As we have seen in real life, AutoCAD provides a three-dimensional space, and usually our modeling work is done in such a space. AutoCAD systems provide an absolute coordinate system for this three-dimensional space and call it the world coordinate system (Wcs,world coordinate system), which exists in any graph and cannot be changed. This section discusses a special case of this coordinate system--the plane coordinate system (that is, the third dimensional coordinate is always 0), and for the three-dimensional coordinate system, see 19.1.

2.4.1 Cartesian coordinate system

The Cartesian coordinate system, also known as the rectangular coordinate system, consists of a single origin (0,0) and two axes perpendicular to each other through the origin (see Figure 2-11). Where the axis in the horizontal direction is the x-axis, to the right of its positive direction, the vertical axis is the y axis, to its positive direction. Any point p on the plane can be defined by the coordinates of the x and Y axes, that is, a pair of coordinate values (x,y) to define a point.

For example, the rectangular coordinates of a point are (3,4).

2.4.2 Polar coordinate system

Polar coordinates are composed of a pole and a polar axis (see figure 2-12), and the direction of the polar axis is horizontally to the right. Any point on the plane p can be defined by the line length L (>0) of the point to the pole and the intersection of the line and the polar axis (polar angle, counterclockwise direction), that is, a pair of coordinate values (L<A) to define a point where "<" represents an angle.

For example, the polar coordinates of a point are (5<30).

2.4.3 Relative coordinates

In some cases, the user needs to draw the graph directly through the relative displacement of the point to the point, rather than specifying the absolute coordinates of each point. For this reason, AutoCAD provides a way to use relative coordinates. The so-called relative coordinates, is a point and relative point of relative displacement value, in AutoCAD relative coordinates with "@" logo. You can use Cartesian coordinates when using relative coordinates, or you can use polar coordinates, depending on the situation.

For example, a line with a starting point coordinate (5,5), an endpoint coordinate (10,5), and a relative coordinate of the endpoint relative to the starting point (@5,0), expressed in relative polar coordinates (@5<0).