In gCADPlus, 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. Coordinates may be entered as either Cartesian or polar coordinates.

Cartesian coord​inates

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. 

Polar coordinates
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). gCADPlus does not allow the use of the 3rd dimension, so it can be ignored even though a value for the Z plane will be 0 - 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. 
 
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.
 
Relative coordinates
The following example draws a second 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.
 
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.
The following example shows a line drawn with polar coordinates using the default angle direction setting. Pressing ENTER at the Next To Point prompt ends the command.
 
polar coordinates 2
The following example shows a line drawn with relative polar coordinates. Pressing ENTER at the Next To Point prompt ends the command.
 
relative polar
 
 
Also you can specify direction angle by mouse position relative to last entered point. At this case you specify only distance value in the command line, and gCADPlus will use the coordinates of the point which are placed at specified distance from the last entered point along a direction to cursor position. 

Coordinate systems