Command Entry, Corrections and Coordinates



Lesson 1b: Creating a Drawing, Command Entry, Corrections, Objects and Coordinates

Objectives: at the end of this lesson the user should understand:

1. configuring the workspace

2. the basic process of creating a drawing

3. three best ways to enter a command

4. correcting command errors

5. coordinate system

6. five ways to define coordinates

1. Configuring the workspace

Step-by-step instructions for starting AutoCAD 2012 are given in the instructions for lab period 2.

AutoCAD 2012 initially begins using the Drafting & Annotation * workspace

as shown in the following figure.

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An alternate and still popular workspace is AutoCAD classic which is brought up as shown in the following figure.

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Selecting AutoCAD Classic changes the workspace to appear as shown in the following figure.

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The textbook uses the Drafting & Annotation workspace

2. The basic process of creating a drawing

Once AutoCAD is running in Classic workspace mode, one can begin creating a drawing but first the important areas of the workspace should be noted

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Drawings are usually started by opening:

* a standard template or

* an existing standard drawing that contains items such as a border and title block.

In this course an existing standard drawing will be opened and is shown in the figure below.

The procedure to open an MIME 1100 standard drawing, as shown below, will be explained in detail during the laboratory period.

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To create a drawing, the user enters commands to create entities or objects including

* lines, arcs, circles and other geometric entities.

* and text and dimensions.

The geometry creation commands such as line and circle the require coordinates or dimensions be entered.

In the sections that follow command entry will be discussed first, followed by coordinate entry

Commands can also be given to modify or change the entities or objects.

Once the drawing is complete, a hardcopy can be plotted.

As the drawing proceeds, one should periodically save the drawing so all work is not lost if the system crashes.

3. Three Best Ways to Enter a Command

To create and modify geometry commands are given.

The easiest three ways to give commands are shown in the following figures with the command being given to draw a line.

Method 1 select the command from a panel

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Method 2 type commands

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Method 3 click on toolbars

To display tool bars if using the Drafting and Annotation workspace are shown in the next figure.

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To control what toolbars are displayed right click on any toolbar header and check/uncheck the toolbars to be displayed/not displayed.

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4. Correcting errors in commands

Table 4.1 Error Correcting

|Error |Action |

|Command is wrong and Space or Enter has not been pushed |Backspace or delete key – corrects typing errors |

| |Esc key – deletes all characters on current command line |

|Command has been entered and options are being selected |Esc key – aborts the command |

|Command has been completed and result is not what was desired |Typing Undo undoes previous command |

| |Undo 3 undoes the last 3 commands etc. |

| |If too much is undone, Redo will executed undone commands again. |

|Previous work is incorrect |The Erase command permits geometry to be selected which are then |

| |erased when Enter is pushed. |

5. Coordinate System and Positive Angles

A coordinate system or reference system is required to * dimension and position objects.

AutoCAD uses * a right-handed coordinate system.

The coordinate system used to define entities in AutoCAD is referred to as the User Coordinate System or UCS.

A coordinate system icon can be turned on/off in the drawing area of the window with the UCSICON command.

6. Five Methods of Specifying the Position of Points

Let’s assume one wishes to draw a rectangle with its lower left corner at 1,1 that is 3 units wide and 2 unit high.

6.1 Interactive – * simply clicking on points

Trying to watch the coordinates in the lower left corner of the window and clicking at precisely the correct position is very difficult.

If points are to be enter interactively, usually a grid of points are displayed and the system is asked to snap to the points. The two relevant commands are

* GRID and SNAP

For example a rectangle that is 3 units wide and 2 units tall is to be drawn with its lower left corner at x = 1, y = 1.

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6.2 Absolute Cartesian – type in coordinates relative to * User Coordinate System, UCS

Format: * x_value,y_value Example: 3,2

The example below shows the same rectangle that was drawn previously drawn with absolute coordinates.

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6.3 Relative Cartesian Coordinate – type in coordinates relative to * the current point.

The current point is * the last point that was entered.

Format: * @x_value,y_value Example @3,2

The @ is entered by typing shift 2

The example below shows the same rectangle that was drawn previously drawn with relative Cartesian coordinates.

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6.4 Absolute polar – type in polar coordinates relative to the * UCS.

Polar coordinates are specified by giving a * length and an angle from the +x UCS axis.

Format: * length_value ................
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