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      When working in two dimensions, you specify points on the xy plane. You can specify any point as an absolute coordinate (or Cartesian coordinate), using the exact x coordinate and y coordinate locations relative to the origin (the (0,0) coordinate point at which the two axes intersect), or as a relative coordinate in relation to the previous point. You can also specify points using relative or absolute polar coordinates, which locate a point using a distance and an angle.

Entering absolute Cartesian coordinates

        The 2D plane is a XY plane, also called construction plane. The 2D plane is similar to a flat sheet of grid paper. If you want to use Cartesian coordinate values to specify a point, enter an X value and Y value separated by a comma (X, Y). The X value of a Cartesian coordinate is the positive or negative distance, in units, along the X axis. The Y value of a Cartesian coordinate is the positive or negative distance, in units, along the Y axis. The origin (0, 0) indicates where the X, Y axes intersect.

       To enter absolute Cartesian coordinates, type the coordinate location of the point in the command bar. For example, to use absolute Cartesian coordinates to draw a line from the origin (0,0) to a point 3 units to the right and 1 unit above the origin, start the Line command and respond to the prompts as follows:

Start of line: 0,0

Angle/Length/<End point>: 3,1

Drawing a line using the absolute Cartesian coordinate method.

Entering relative Cartesian coordinates

        Another, simpler method is to use relative Cartesian coordinates: you specify a location in the drawing by determining its position relative to the last coordinate you specified. To use relative Cartesian coordinates, type the coordinate values in the command bar, preceded by the at symbol (@). The coordinate pair following the @ symbol represents the distance along the xaxis and the y axis to the next point. For example, to draw an 8.5 unit square with its lower left corner at 4,5 using relative Cartesian coordinates, start the Line command, and then respond to the prompts as follows:

Start of line: 4,5

Angle/Length/<End point>: @8.5,0

Angle/Length/Follow/Undo/<End point>: @0,8.5

Angle/Length/Follow/Close/Undo/<End point>: @-8.5,0

Angle/Length/Follow/Close/Undo/<End point>: C

Drawing a square using the relative Cartesian coordinates method; enter C to close.

       The first relative coordinate (@8.5,0) locates the new point 8.5 units to the right (along the x axis) from the previous point of 4,5; the second relative coordinate (@0,8.5) locates the next point 8.5 units above (along the y axis) the previous point, and so on. Entering C (for Close) draws the final line segment back to the first point specified when you started the Line command.

Entering polar coordinates

        Using relative polar coordinates makes drawing a square tilted at a 45 degree angle a simple task. Polar coordinates base the location of a point on a distance and angle from either the origin (absolute coordinate) or from the previous point (relative coordinate).

      To specify polar coordinates, type a distance and an angle, separated by the open angle bracket (<). For example, to use relative polar coordinates to specify a point 1 unit away from the previous point and at an angle of 45 degrees, type @1<45.

      To draw the square from the example in the previous section, "Entering relative Cartesian coordinates," this time tilted at a 45 degree angle, start the Line command, and then respond to the prompts as follows:

Start of line: 4,5

Angle/Length/<End point>: @8.5<45

Angle/Length/Follow/Undo/<End point>: @8.5<315

Angle/Length/Follow/Close/Und/<End point>: @8.5<225

Angle/Length/Follow/Close/Undo/<End point>: C

   Drawing a tilted square using the relative polar coordinates method; enter C to close.

NOTE This example, like all examples in this guide, assumes the program's default settings: Angles increase counterclockwise and decrease clockwise. Thus, an angle of 315 degrees is the same as 45 degrees.

Commands Reference

BLIPMODE: Controls the display of marker blips

ID: Displays the coordinate of a location

LIST: Displays database information for selected objects

GRID: Displays a dot grid in the current viewport

SNAP: Restricts cursor movement to specified intervals

TABLET: Calibrates, configures, and turns on and off an attached digitizing tablet

UCS: Manages user coordinate systems

UCSICON: Manages defined user coordinate systems

UNITS: Controls coordinate and angle display formats and precision

System Variables Reference

BLIPMODE: Controls whether marker blips are visible

COORDS: Controls when coordinates are updated on the status line

LASTPOINT: Stores the last point entered, expressed as a UCS coordinate for the current space; referenced by the at symbol (@) during keyboard entry

ELEVATION: Stores the current elevation relative to the current UCS for the current viewport in the current space

TABMODE: Controls the use of the tablet