Tuesday

Autocad, Basics

Understanding Coordinate Input in AutoCAD

Hello Daily AutoCAD readers,

Those who have just started working with AutoCAD should first learn about the coordinate system of AutoCAD. When you first open AutoCAD, you see Model Space on your screen and you make your drawing in this space. You can think of the model space as a 3 dimensional paper space. Indeed, if you are going to draw something 2 dimensional and you are looking at the model from top view, then you can think of it as paper directly. Only difference between paper is that model space has no boundaries. If we remember the old days, we used to make a preliminary preparation to align the drawing in the middle of the paper by adjusting the scale also. In AutoCAD, you don’t have to worry about scaling or aligning the drawing in the middle of the paper. You can read my article “Understanding scale concept and units in Autocad” where I have explained these concepts in detail.When you first start drawing in model space in AutoCAD, probably you will mostly encounter with the problem of entering points. AutoCAD will prompt you to enter a point a strating point of a line, corner of a rectangle etc. In this article, I will explain “how to enter a point” as well as the coordinate system.

In how many different ways can we enter a point?

Answer of this question is 3. When you first step into the world of drawing with AutoCAD, for instance when you use LINE command, AutoCAD will ask you to enter a starting point first.

Command: LINE
From point:

Here are the answers that you can give to this “From point:” question:

• By entering real coordinates.
• By entering relative coordinates.
• By entering coordinates by using AutoCAD drawing aid tools.

Now, let’s make our first step into drawing and learn about coordinate system by going over these topics.

1. Entering absolute coordinates

Command: LINE
From point: -2,1
To Point : 3,4
To point :

Fig.1

In the example given above, we drew the line shown in Fig. 1. We gave the point information that is asked by AutoCAD by entering real coordinates in form of x,y. Let’s continue to convert it into a triangle.

Command: LINE
From point: 3,4
To Point : 3,1
To point : -2,1
To point :

As you can see, it very laborious and time consuming to make drawing by this way. Of course, AutoCAD is equipped with many point entering methods to make drawing work faster and more practical. In this part, we entered cartesian coordinates. Now, let’s draw the same triangle by using more advanced methods.

2. Entering relative coordinates:

Entering relative coordinates is entering another point as referenced to another point as it can be understood from its name. There are various methods in AutoCAD that can be used to enter relative coordinates. Let’s make the previous example by using relative coordinates. Let’s draw the same triangle by starting from -2,1 point, going 5 units in right direction and 3 units in upper direction and end in same -2,1 point.

Command: LINE
From point: -2,1
To Point : @5,0
To point : @0,3
To point : c

Fig.2

As you can see, entering relative coordinates is done by using @ symbol from the last point and entering Δx,Δy values. @ means that we will enter relative coordinates.

3. Polar Coordinates:

Other that cartesian (x,y) coordinates, another coordinate system that you can use to enter points is POLAR coordinates system. It is a coordinate that is reached by a distance and an angle from a certain origin point. We know that angles increase in counter clockwise direction in AutoCAD ( Fig. 3).

Fig.3

After reminding this information, let’s continue to know more about POLAR coordinates. The example given in Fig. 4 explains how to enter polar coordinates by using relative coordinates.

Command:_LINE
From point: #0,0
To point: #4<120
To point: #5<30

Fig.4

Even though we are not at the topic of relative coordinates, this example is given in order not to skip entering absolute polar coordinates. # symbol at the beginning is used to mention the absolute coordinate entry. Now, let me give an example for entering relative polar coordinates.

Fig.5

Let’s go over the previous example:

Command:_LINE
From point: @3<45
To point: @5<285

As you can see, by entering @ symbol, you are saying “relative to last point”. @3<45 expression means 3 units at 45 degrees relative to the last point, then we move 5 units with 75 degrees by using @5<285 expression. You can also draw yourself a square by starting from any point.

Command:_LINE
From point:
From point: @5<0
From point: @5<90
From point: @5<180
From point: c

As you can see, entering relative coordinates is very useful to use. Thus, it is the method that is most frequently used. However, relative Cartesians mat also be used for very rare subjects like drawing a rectangle.

Command:_RECTANG
First corner:
Other corner: @5,3

This example draws a rectangle with dimensions 5×3.

3. Entering coordinates by using AutoCAD drawing aid (dynamic) tools:

If you select a point on the screen by using you mouse cursor, then you cannot enter and exact coordinate. Of course, it would be better if we could have entered the exact coordinate that we wanted just by using the mouse cursor. Since AutoCAD 2000, entering coordinates by using mouse cursor has been improved. And in final versions AutoCAD 2006 and 2007, this has been improved even better. This is called dynamic coordinate entry in AutoCAD. Now, let’s take a look the subject by giving some examples:

Angle by cursor, but distance is dynamic

Fig.6

As you move your cursor and approach to angles that are defined in POLAR settings, then you will see that your cursor is locked on that angle. As the cursor is locked, then we can move as much as we want that along the angle we are locked onto.

Angle locked, distance is dynamic

Fig.7

After selecting the first point to draw a line, if you write <45 and press ENTER, then you lock the cursor on 45 degrees. You can enter distance either by your hand or again by using cursor.

Distance locked, but angle is dynamic:

Fig.8

When we write 200<, then distance will be locked at 200 units and you will be prompted to enter an angle value. Lock is broken at angles specified at POLAR settings.

In future, I will give a second lesson about this subject. That’s all for now about coordinate entries. I hope it will be useful for you.

Have a nice day…

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