When creating a drawing in AutoCAD, we will need to define many points, such as the start point, end point, center point, etc. To determine the location of these points efficiently and accurately, we need to learn about AutoCAD Coordinate Systems and also learn about how to determine the location of points in AutoCAD.
Let’s start from the first one.
A. Coordinate Systems
In AutoCAD, we can determine the coordinates of points using two coordinate systems, namely Cartesian Coordinate System and Polar Coordinate System.
In Cartesian coordinates, the location of a point is determined by the X (up/down) and Y (right/left) values. Meanwhile, the polar coordinate system uses the distance between points as a length or magnitude value, and uses angle values to determine direction or vectors.
The system you use will depend upon the information you have. If you know the grid position, use Cartesian coordinates. However, if you know the exact angle between two points and their distance, use Polar coordinates.
For more details, see the image below:
B. Methods for Determining Point Location
There are 6 methods to determine the location of a point on the AutoCAD work screen. Below is an explanation of them.
1. Interactive Method
This method has a function to determine a point by clicking directly on the screen using the cursor. This method is the least accurate unless you enable OSNAP.
2. Absolute Cartesian Coordinate Method
This is a method for determining point location by typing the x and y coordinate values into command line. All coordinate values in this method are relative to the origin (0,0).
Format for writing coordinates in the Absolute Cartesian method is: x,y
- x : coordinate value for X axis
- y : coordinate value for Y axis.
- The x and y values are separated using a comma (,) without spaces.
3. Relative Cartesian Coordinate Method
This is also a method for determining point location by typing the x and y coordinate values into the command line. But, all coordinate values in this method are relative to the previous point in one command.
Because the coordinate values in this method are relative to the previous point, So we cannot use this method to determine the first point.
Format for writing coordinates in the Relative Cartesian method is: @x,y
4. Relative Polar Coordinate Method
This method has a function to to determine the location of a point based on the distance and angle from the previous point. This method also cannot be used to determine the first point.
Format for writing coordinates in the Relative Polar method is: @distance<angle
- Distance : means the direct distance value of the point to be created from the previous point.
- Angle : the angle value of the point to be created relative to the previous point.
5. Direct Distance Entry Method
This method allows you to determine the location of a point by entering the distance directly from the previous point.
To use it, move the cursor away from the previous point in the desired direction, then type the desired distance and press Enter. For accurate results, use ORTHO or Polar Tracking.
6. Surveyors Coordinates
This method is almost the same as Relative Polar, only the writing is different. It is used to map areas.
An example of writing coordinates using this method is @100<n30d45’e. This means the direct distance from the previous point is 100 units and the direction is North 30°45′ East.
C. Example
In this section we will learn to determine the point locations using various methods.
See the image below:
1. To Point B from Point A :
- Absolute Cartesian coordinates: 0,0 (A) and 4,4 (B)
- Relative Cartesian coordinates for Point B: 0,0 (A) and @4,4 (B)
- Interactive method can be used by clicking directly on the work screen when the Grid Snap feature is active with Snap Distance set to 1, 2 or 4.
2. To Point D from Point C :
- Absolute Cartesian coordinates: -3,0 (C) and -3,4 (D)
- Relative Cartesian coordinates for Point D: -3,0 (C) and @0,4 (D)
- Relative Polar Coordinates for Point D: -3,0 (C) and @4<90 (D)
- Direct Distance Entry for Point D: -3,0 (C) and 4 (D) with Ortho on and cursor above Point C
- Interactive method can be used by clicking directly on the work screen when the Grid Snap feature is active with Snap Distance set to 1, 2 or 4.
3. To Point F from Point E :
- Absolute Cartesian coordinates: -3,-4 (E) and 3,-2 (F)
- Relative Cartesian coordinates for Point F: -3,-4 (E) and @6,2 (F)
- Interactive method can be used by clicking directly on the work screen when the Grid Snap feature is active with Snap Distance set to 1 or 2.
Note: From point A to point B and from point E to point F, the Polar Relative Coordinate method cannot be used because the direct distance between two points is unknown. Of course, we can calculate it first, but that would be inefficient.
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