Defining coordinates
An essential step in all CAD programs is to draw with precision. Defining entity points like endpoints of a segment line or a circle center, without any doubt is a constant process, which can be achieved by introducing coordinates, absolute or relative. There are also several auxiliary tools that ease the process, as shown later in the chapter.
Absolute coordinates
DraftSight uses a Cartesian system, with an origin and three orthographic axes: X, Y, and Z. All points are referenced with coordinates related to these axes. In 2D drawings, the Z coordinate can be omitted.
So, to define a 2D point in absolute coordinates, two values must be set: the first along the X axis and the second along the Y axis, separated by a comma:
X_value,Y_value
Examples, as displayed in following diagram, are the points -2,3; -3,-2; 1,-2; or 4,2.
Relative Cartesian coordinates
Often, points are defined relating to the last introduced point. To specify a point in relative Cartesian coordinates, an at the rate symbol (@) must be introduced, followed by increment in X direction, a comma, and increment in Y direction:
@increment_X,increment_Y
Of course one of these values may be zero. If both are zero (@0,0), this means that the point is coincident with the last one. For instance, in the next image, if point A is the last point defined, point B can be given by @2,1 and point C, after B being introduced, can be given by @-1,2.
Relative polar coordinates
Sometimes, increments between points are not known. Instead we know the direct distance and angle between points. In these situations, it is preferable to apply relative polar coordinates, starting by the @ symbol, followed by the distance, left angle bracket as the angle symbol, and the absolute angle:
@distance<angle
Angles, as displayed in following diagram, by default are in decimal degrees, measured positive counter-clockwise and the zero degrees corresponds to East.
