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.

**Cartesian 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.