The User Coordinate System

how does AutoCAD know where your objects are well it uses a Cartesian coordinate system known as the user coordinate system or the UCS when you turn AutoCAD on and open up a drawing you might have noticed the two arrows that appear at the bottom left portion of your screen down here
that is the UCS icon it’s there to help you keep track of your coordinate system now this is where AutoCAD and autocad LT are slightly different what I’m doing here now in this example has been done in autocad so i want to show you in both ways the way autocad and the way autocad LT handles it the x and y axes are the same in autocad as in autocad LT where they differ is in the third axis and we’ll talk about that in a little bit but if you have ever plotted points on an x and y graph or chart in math class or somewhere then you are familiar with a coordinate system autocad’s UCS again the user coordinate system is a fairly typical coordinate system the numbers in the X direction on the x-axis are the horizontal axis left and right of your screen the Y coordinates right here the wine are for your vertical coordinates so X is horizontal why is vertical vertical meaning straight up and down on your screen there is a third axis that’s the z axis so that little square comes it comes and sticks right out at you comes right out of your screen now this axis isn’t really accessible in AutoCAD LT but if you’re using AutoCAD LT and you open up a drawing that was made in regular AutoCAD in that file has objects that are drawn in it there there it’s just going to be a little tricky to access them so just be careful the three axes together create a 3d grid and autocad LT is there’s just a 2d grid and we use these two drawing as you rotate your grid like this and you can only do this in AutoCAD if you’re doing autocad LT you’re only going to be able to rotate in your X and y-axis you can kind of get a better picture of what all three axes look like I’d rotated the screen by pressing the shift key down holding it and then pressing and holding the middle mouse button this performs a 3d orbit in AutoCAD but not in AutoCAD LT so you can kind of see what it looks like and you can reposition your user coordinate system in a lot of different ways and that will help you to draw different objects
so if i want to draw a rectangle I can it’s still drawing in the X and Y plane
can see it’s flat
a little bit later on but to return just type in the word plan click on world and that will reset you to the regular XY plane in each coordinate along an axis is one unit long as you move your mouse back and forth you can see in the bottom left-hand corner my coordinates these are your drawing coordinates so you can turn those off and on by pressing ctrl and I
as I move around it tells me what coordinates I’m in
pretty handy so it gives you an idea of where you are and what you need to know you can also learn a few things about none of the sizes of things I can see my coordinates here and do some quick math and that’ll let me know that this is about a unit along
so the coordinates can be used a lot of different ways the number on the left as with most standard Cartesian coordinate systems is the value of the point on the x-axis or the horizontal axis in this case the number in the center is of the y axis or the vertical axis here and then the third value is the z axis as you can see as I move around this plane and in autocad LT it’s at zero so let’s draw some lines and find their
coordinates so just start in a blank file and draw a line type in alpha line and then pick a point anywhere
and draw it to somewhere else in the press center
so we want to find the coordinates for the endpoints of the line select the line and these blue boxes that are on the either the endpoints and one on the midpoint of the line are called grips I’ll show you how to use grips to edit and to work in AutoCAD later on but right now you’re going to just put your mouse right on it and as you see in the bottom left-hand corner those are the coordinates for that point so you can write that down and then as you move your mouse the coordinates change and if you hover over that other grip you get the coordinates for that point and you can do the same thing with this box
get your coordinates and then you can plot it out on a graph or you can use those four points to locate something else
as you move left or down the screen the values of the coordinates decrease as you move up or to the right the values become larger well every coordinate system has an origin and it’s typically found at the coordinates of 0 comma 0 well that’s the same case here we’re at zero comma zero autocad works the same way so that also means that you can have negative coordinates and autocad and in math the positive and negative values often indicate direction so a positive direction in a line or in a coordinate means it’s moving to the right or up negative is going left or down it’s the same sort of thing when I move over here to the left and lower of the UCS icon you can see my coordinates are negative to the top right they’re positive and the x and y become positive and negative accordingly he could draw objects to distances or you can draw them to static coordinate points for example let’s draw a line that starts at the origin and goes to coordinate 3 comma 4 so I start the line command and whenever you start off something you can always just type in the coordinates so put in 0 and hit the tab key or hit the comma key either one in this case and we want zero press ENTER and my line is now started at the origin or at 0 comma 0 now it’s a little tricky on your next point your second point you have to tell autocad that you want to put in the exact coordinates otherwise it’s going to put in distances and angles so you have to hit the pound key that will tell autocad that you mean a coordinate so we want to put this at coordinate 3 comma 4 so i hit three and you can’t hit tab here if you hit tab then it’s going to go to the angle so you’ll be drawing in a length and angle but if you press in the comma key it tells autocad hey i’m drawing this you know in coordinate so we now type in the number four and this we’ll put our second point at coordinate three comma four press Enter
so there’s our line now we can check it let’s select it and hover on it then you can see the coordinate system in the bottom left that says it’s at three comma four we did it so you can always graph to specific points you can draw distances you can draw it angles but if you know your coordinates you can draw accordingly and this is how surveyors will draw an AutoCAD they will typically need to work on some sort of coordinate system in the United States we use a lot of state planes coordinate systems and that’s origin is set at some arbitrary point in the real world that’s at 0 comma 0 and then they may go thousands of units away because they’re usually covering large areas and you can draw from point to point so this is a very useful and just another way of drawing in AutoCAD

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