1. Drawing with Precision
Lesson 2
This information presented in this slide show is going to seem like a math review. If it seems very elementary good. If it seems like Greek sit tight and hopefully by the end of the evening it will become clear. If you have any questions please stop me and ask.

2. Now that you can draw objects……
4” DIA.
So far you have been creating objects in the drawing area by selecting points on the screen with the mouse. You can certainly use Cad as a sketching device and not worry about precision but, most often objects are required to be a specific size and location.
Let’s create them to a specific size and location. 5”

3. The UCS icon User Coordinate System x,y,z
We discovered the UCS icon located in the lower left hand corner of your drawing area when we identified the different areas of the screen. This icon is somewhat like a compass in that it alerts the user the direction of the x and y and z axis. The creators of AutoCAD chose to use a W instead of a Z because they refer to it as a World Coordinate System. Unlike some cad softwares, AutoCAD is a very powerful 3d tool. Our focus will be on the 2d capabilities.

4. How objects are graphed.Y
(-,+)
(+,+)
(-2,3)
(4,1) X
0,0
This graph should look familiar to you from your geometry class. The AutoCAD screen acts as an infinite graph. It has an origin, (0,0) and four quadrants and coordinates are graphed mathematically just as you would expect them to.
(-,-)
(+,-)

5. How is this communicated to CAD?
So how do you go from selecting points with your mouse to entering exact coordinates? Each time you invoke a command the command window displays text to que you as to how it is accomplishing the requested task. On this slide the line command has been entered. Remember the first class we discussed that there is more than one way to invoke the same command. The underscore in front of the word line lets you know that the command was entered using the line icon instead of from the command line. The program then prompts you to Specify first point: Notice what coordinates I entered? If I had taken my mouse and selected an arbitrary point on the screen, the points I selected would be recorded by the program but they are not displayed in the command window. Once the first point is specified the program prompts you to Specify next point or allows you the undo option.
At the command line.

6. Variety is good! Absolute Cartesian= x,y Relative Cartesian = @x,y
Relative Polar
Keeping track of coordinates can get cumbersome so the programmers created easier ways to enter the information to achieve the same results. There are basically three methods used to enter coordinates from the command line. Memorizing the terms is not necessary to use the program but if you plan to seek certification and take any type of certification test, please know that questions will be asked using these terms. Why do you think it is necessary to have an understanding of all three? (allow participants to suggest reasons.) The method you use will be dictated by the information you are given to draw from. We will go over some examples later to make this more clear.

7. Three methods, one result.
9” line
Absolute Cartesian
Relative Cartesian
Relative Polar
The term Cartesian comes from the last name of a mathematician and simply signifies that you are dealing with an x and y value. I am using whole numbers in these examples but please know that cad can be much more precise. The term Polar means that points all revolve around a given axis. The angle symbol is used to communicate with the program that you are entering a direction rather than a point. Instead of using an x and y coordinate a distance and a direction is specified. The term absolute means that all points are calculated from the true origin (0,0). The term relative, signified by symbol means that the points are calculated from the last point entered vs the true origin. Now, don’t let all of this technical jargon get you down. If this seems a little fuzzy now, once you put it to use it will become more clear.
Start point=2,2
End point=11,2
Start point=2,2
End
Start point=2,2
End

8. Absolute Cartesian 1) 3,3 2) 11,3 3) 11,9 4) 3,9 3 4 1 2 0,0
1) 3,3
2) 11,3
3) 11,9
4) 3,9 3 4
Using the line command if you enter these coordinates each time the program prompts you to specify a point, this will be the result. 1 2
0,0

9. Relative Cartesian (@)
1) 3,3 3 4
Using the line command if you enter these coordinates each time the program prompts you to specify a point, this will be the result. 1 2
0,0

10. Relative Polar (@) (<)
1) 3,3 3 4
Using the line command if you enter these coordinates each time the program prompts you to specify a point, this will be the result. 1 2
0,0

11. Aim and Fire! Direct Entry Method. So why learn the other methods?
In earlier versions of the software entering coordinates was the only way. Now there is polar tracking that allows you to specify the angle with the mouse and then enter a distance on the keyboard. In order to accomplish this polar tracking must be toggled on. (Status bar or F10) You will know if it is on because the tool-tip will be visible as you see on the slide.
So why learn the other methods?

12. Apply what you learned.
I have a graphing exercise for you to complete on page __ .This will help reinforce the different entry methods.