As an alternative to pointing and clicking when asked to nominate a point, CAD software like gCADPlus (and AutoCAD) allow direct entry of coordinate locations.So, when a command prompts you for a point, you can use the pointing device (your mouse) to specify a point by clicking, or you can enter a coordinate value on the command line. You can enter coordinates as either Cartesian or polar coordinates.
A Cartesian coordinate system has three axes, X, Y, and Z. When you enter coordinate values, you indicate a point’s distance (in units) and its direction (+ or -) along the X, Y, and Z axes relative to the coordinate system’s point of origin where all coordinate values are zero (0,0,0). Negative values on the X plane are left of the point of origin, and positive values on the X plane are to the right of the point of origin. Negative values on the Y plane are below the point of origin and positive values on the Y plane are above it. Positive values for the Z plane indicate an elevation while negative values in the Z plane indicate a depression, or a point beyond the point of origin.
Polar coordinates use a distance and a fixed angle to locate a point. With both Cartesian and polar coordinates, you can enter absolute coordinates based on the point of origin (0,0,0), or relative coordinates based on the last point specified.
Entering Cartesian Coordinates
To use a coordinate to specify a point, enter an X value and a Y value separated by a comma (X,Y). If using the 3rd dimension, add a value for the Z plane as well and the coordinate set will appear as: (X,Y,Z). The X value is the positive or negative distance, in units, along the horizontal axis. The Y value is the positive or negative distance, in units, along the vertical axis. The Z value is the positive or negative distance, in units, along the elevation-depth axis. The remaining portion of this topic deals only with two dimensions, but the Z coordinate is applicable as desired.
Absolute coordinate values are based on the origin (0,0), where the X and Y axes intersect. Use an absolute coordinate when you know the precise X and Y values of the point coordinate. For example, the coordinate 3,4 specifies a point 3 units along the X axis and 4 units along the Y axis from the origin.
Relative coordinate values are based on the last point entered. Use a relative coordinate when you know the position of a point in relation to the previous point. To specify a relative coordinate, precede the coordinate with an @ symbol. For example, the coordinate @3,4 specifies a point 3 units along the X axis and 4 units along the Y axis from the last point specified.
The following example draws a line beginning at a point with an X value of -2, a Y value of 1, and an endpoint at 3,4. Pressing ENTER at the To Point prompt ends the command.
The following example draws a line whose endpoint is 5 units in the X direction and 0 units in the Y direction from the start point at the absolute coordinate -2,1. Pressing ENTER at the next To Point prompt ends the command.
Entering Polar Coordinates
To enter a polar coordinate, enter a distance and an angle separated by an angle bracket (<). For example, to specify a point that is at a distance of 1 unit from the previous point and at an angle of 45 degrees, enter @1<45.
By default, angles increase in the counterclockwise direction and decrease in the clockwise direction. To move clockwise, enter a negative value for the angle. For example, entering 1<315 is the same as entering 1<-45.
Polar coordinates are either absolute (measured from the origin) or relative to the previous point. To specify a relative coordinate, precede the coordinate with an @ symbol.