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AutoCAD is a computer-aided drafting and design program that is the industry standard for a wide variety of 2D and 3D work. AutoCAD 2008 features several improvements over previous versions, but the core functionality and workflows have remained consistent for years. Users who have any of the more recent editions of the software will find AutoCAD 2008 Essential Training to be a valuable resource. Instructor Jeff Bartels has taught and used AutoCAD for a decade, and in this course he focuses on the difficult to master concepts that matter most to professional AutoCAD users. Exercise files accompany the course.
In this session, we are going to take a closer look at Model space, otherwise known as our drafting board. Our approach is going to be a little bit different because we are going to look at a Model space from the computer's point of view. Taking this behind the scenes look can be very helpful in teaching us how AutoCAD maintains our line work. Model space is essentially an infinitely large sheet of graph paper. We use this graph paper to construct our geometry and AutoCAD uses this graph paper to maintain our accuracy. AutoCAD maintains our accuracy through the use of baselines.
The first baseline I want to talk about is a major east/west baseline, otherwise known as the X-axis. Now, the X-axis is also a number line and any value to the right of zero is considered positive x, any value to the left of zero is considered negative x. Now, there is another baseline AutoCAD uses. This is a major north/south baseline, it is called the Y-axis. The Y-axis is also a number line. Any value above the X-axis is considered a positive y, anything below the X-axis is considered negative y. This system of using an x and y axis to organize our locations and space is called the Cartesian Coordinates system.
Now, this graph paper that we see on screen is completely invisible when we draft. We won't see this as we draw, but it is there. It is going on in the background and AutoCAD uses this system to organize our geometry. AutoCAD uses the Cartesian Coordinates system to identify all locations and space. Now, AutoCAD uses a fancy name for locations and space, AutoCAD uses the word coordinates. AutoCAD references coordinates using the format x, y. Now, take a look at the area where the x and y axis intersect.
That intersection has a coordinate value of 0,0 because each of the axes is intersecting at the zero location. Now, the intersection of the x and y axis also has a name, it's called the origin. All AutoCAD coordinates are measured from the origin. For instance, I am going to bring some points up on screen. We will see how this works. If I wish to bring up a location right here, this guy has a coordinate value of 4,2. That's because he is 4 units in the positive x direction and he is 2 units in the y direction.
It's kind of like playing Battleship. Let me bring up another point. Let's look at this guy. This guy has a coordinate value of 3,9, because he is 3 over in the x and he is 9 up in the y. Let's pop up another one. What about this coordinate? This guy has a value of -6,4, he is -6 in the x direction and he is 4 in the y direction. Last one, we bring up one down here. This guy has a coordinate value of -5,-7. He is -5 in the x and he is -7 in the y.
Let's look at the Cartesian Coordinates system from my perspective. Let's assume I am creating a line in AutoCAD. If I am creating a line, I start out by picking my start point and then I pick my end point to complete my life. Let's look at how AutoCAD views this line. AutoCAD views this as a line segment that was drawn from coordinate -8,-3 to coordinate 8,10. Now, I am going to return to my AutoCAD environment. Now that we understand how coordinates work, I want you to take a look at the lower left-hand corner of our screen in our status bar.
Remember, this is the area that represents the current coordinate location of our cursor. Hopefully, this makes more sense now as I move my cursor, we can see the exact location on my invisible graph paper where my cursor is located. One more thing, take a look at this guy in the lower left-hand corner. This is our UCS icon. This icon right now is telling us the current direction of our positive X-axis and our positive Y-axis. I would I like to create a couple pieces of geometry using coordinates. Before I start, I am going to come down and I am going to turn off my Heads Up display, I am going to turn off my Dynamic Input.
This guy tends to take some liberties when we are entering coordinate values. And if I turn him off temporarily, we won't have any problems. Let's create a circle and this time, I am going to place it using coordinates. I am going to come over and launch my Circle command by clicking on it and AutoCAD says specify center point for my circle. I am going to type in 25,25. I am typing in an actual coordinate where I want the center of that circle to be located. Let me hit Enter. I am creating that circle at coordinate 25,25. As far as my radius, I am going to type in 10.
We will just create a circle with a radius of 10. Let's make one more circle. I am going to right-click, select Repeat Circle. Specify center point. I am going to use the coordinate 75,25. Now hit Enter. Based on my coordinate values, the circle happens to be 50 units to the right of the first circle. And I am going to hit Enter and accept the default because I want to create the same size circle. Each of these circles was drawn using a coordinate. I want to do one more thing. Let's take and draw a line from the center of one circle to the center of the other.
I am going to launch the Line command. I would like to draw a line from the center of this circle and I happen to know what that coordinate is. So I am going to type in 25,25 from my coordinate. I will hit Enter, that's where I am starting from. I would like to draw this line to the center of this circle and we happen to know what its coordinate is. Let me type in 75,25 and hit Enter. I am all done with the command. So I am going to right-click and select Enter to exit. Most of the time, we will not be entering coordinates as we draft.
However, it is important for you to understand the fundamental way AutoCAD processes our line work in the background. Think of it this way. AutoCAD is a vector application whose job is simply creating and maintaining geometry. Everything we draft is mapped out on an underlined x/y coordinate system and AutoCAD uses this system to maintain the accuracy of our drawings.
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