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What are absolute coordinates and relative coordinates in CAD? How to enter coordinates using different methods?

What are absolute coordinates and relative coordinates in CAD? How to enter coordinates using different methods?

Sometimes we know the exact coordinates, but sometimes we only know the angle and distance.

We need to pinpoint a point using different methods based on what we’ve known. Therefore, the CAD system provides many ways to enter coordinates.

The common methods to enter coordinates in CAD is to enter X, Y coordinate values in 2D drawings and enter X, Y, Z coordinate values in 3D drawings. In addition to these, the CAD system also provides polar coordinates, cylindrical coordinates, spherical coordinates. When entering those coordinates, we can either enter absolute coordinate values relative to the origin of the coordinates or enter relative values to the last point.

Absolute coordinates: is distance or angle of axes relative to the origin of the coordinates.

When entering absolute coordinates, enter the coordinates of points in the command bar. For example, entering absolute coordinates needs us to draw a line from point (-3,2) to point (4,4), firstly, enter Line command and then enter as the following shows:

When using absolute coordinates, we’ll need to know the exact position of points of the objects. For example, when drawing a square 8 per side, coordinates for a left lower point is (4,5), then we’ll need to enter points coordinates in clockwise order: left upper point(4,13), right upper point (12,13), right lower point (12,5).

Relative coordinates: the distance or angle of axes relative to the last point. Remember to add @ before entering coordinate values, take @2, 3 for example, it shows the distance from the last point in the X-axis direction is 3 and in the Y-axis direction is 3.

For example, draw a triangle with left lower point (-3,-2) using relative coordinates. Firstly, enter Line command and enter coordinates according to prompts:

Polar coordinates: is to position points by entering distance and angle separated by <. Both absolute coordinates and relative coordinates can be entered, but @ needs to be added when entering relative coordinates such as @ 10< 45.

Coordinates in 3D drawings are similar to those of 2D drawings. If we need to include angle in 3D coordinates, we can include Cylindrical coordinates and Spherical coordinates.

Cylindrical coordinates: in the form of: X < [formed angle with the X-axis], Z, which is polar coordinates in the 2D drawing plus the Z coordinates.

Spherical coordinates: in the form of: X < [formed angle with the X-axis], which is the polar coordinates in the 2D drawings plus the angle of the XY plane.

Most CAD systems have dynamic input(DYN) and we can directly input coordinate values without looking at the command line.

But there are differences between dynamic input and command line input, for example, when we draw a line and inputting absolute coordinates as the first point, but default coordinate for the next point is relative coordinates, then no need to add @ before the coordinates. We can also set absolute coordinates as the dynamic input, as shown in the following picture.

Relative coordinates are set by default in dynamic input, but if we want to change it to absolute coordinates temporarily, we can first input # in the dynamic input box, and then input the coordinate values.

Other than inputting the entire coordinate values, we can also use snap, orthogonal tools or cursor to pinpoint precise position of points. For example, we can use object snap (F3) to directly use cursor to pinpoint to the feature points of an existing object, and use the cursor to indicate direction, for example open orthogonal(F8) and then move cursor horizontally, vertically or form a 45 degree angle with polar axis, then directly input the length of the line without inputting relative coordinates. The following shows the effect of polar axis inputting coordinates after setting the polar axis increment angle to 45.

CAD has provided many precise drawing tools, such as grid, object trap, polar axis, orthogonal, dynamic input, making drawing easier and easier. We don’t have to input the entire coordinates in the daily drawing.

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