Introduction to VB.NET in AutoCAD

VBA is in the process of being phased out, and the replacement is .NET. This may disappoint some of you that have VBA applications/skills, but you will be pleased to hear that you can still use code that you have, and all you know about VBA programming with AutoCAD® can still be put to good use using VB.NET. The following tutorial sets the foundation for creating your first VB.NET project, and should serve as a good starting point for migrating your code across to VB.NET.

What you need

There is no native IDE (integrated development environment) within AutoCAD® for developing .NET projects like you could with VBA (via the command VBAIDE). Instead, you need an external software development package for writing and compiling your code. Fear not however, you can download express editions of several programming suites for free directly from Microsoft’s website. Click here to visit the page for downloading Visual Basic Express 2010.
Next, you need to download the ObjectARX programming interface from AutoDesk’s website. Click here to visit the page for downloading ObjectARX. Ensure you acquire the correct version of the ObjectARX libraries for your version of AutoCAD.

Create your first VB.NET AutoCAD® project

Open Microsoft Visual Basic Express, and select “New Project”, and then select the “Class Library” option. This creates a project that compiles to a dynamic link library (.dll file). In VBA you automatically have access to the AutoCAD® object, including objects such as ThisDrawing, but in this environment we have to create references to AutoCAD® explicitly ourselves. We do this by naming a reference to ObjectARX, which contains the AutoCAD® type libraries that we want to use.

  1. Under the Solution Explorer window, right click on your project (ClassLibrary1 if you haven’t renamed it), and select Properties.
  2. Click on the References Tab.
  3. Click on the Add dropdown, and select Reference.
  4. Click on the Browse Tab, and navigate to where the ObjectARX libraries are installed. Typically this will be C:\ObjectARX 2011\
  5. Depending on your preference, open the folder inc-win32 or inc-x64.
  6. Select the dll files Autodesk.AutoCAD.Interop.dll and Autodesk.AutoCAD.Interop.Common.dll, and click OK. This imports the AutoCAD® type libraries.
  7. Add another reference, and this time select the inc folder. Select AcMgd.dll and AcDbMgd.dll, and click OK. I’m not completely sure why these are required, but apparently they are!
  8. Finally, you’ll notice on the References Tab that the Copy Local property of the AcMgd.dll and AcDbMgd.dll references is set to True. This needs to be False so select them, and under the properties window change the Copy Local property to False.

Writing some initial code

Our project is now set up with all the references required to link to AutoCAD®. Now we can begin writing code.
Switch back to code view (If you haven’t renamed anything, double click on Class1.vb under Solution Explorer). We need to specify in this class which libraries from our references we intend to use, so right at the top of the class (before Public Class Class1) put the following code:

    'Contains the AutoCAD® Type Library
    Imports Autodesk.AutoCAD.Interop
    'Contains the AutoCAD/ObjectDBX Type Library
    Imports Autodesk.AutoCAD.Interop.Common

Now in VBA, we had access to the ThisDrawing object. This is quite useful, so it would be useful to have the same functionality here. Now that we have access to the AutoCAD® object model, we can add a simple Get procedure to retrieve the object we want. Put the following code inside the Class (between Public Class Class1 and End Class):


    Public ReadOnly Property ThisDrawing As AcadDocument
        Get
            Return Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.AcadDocument
        End Get
    End Property

Now we can use ThisDrawing anywhere within the class as we could in VBA.

Writing our first AutoCAD® Function

Everything is in place now to start producing our own AutoCAD® commands. If you have any VBA code you want to transfer across, you should now be able to paste them into this class. Here’s one that I wrote recently as an example. The code adds a border to MTEXT, and the only difference between this code and VBA code is that I’ve made use of the .NET Try/Catch statement, which is better for error trapping than previous methods in VBA:

    Public Sub CreateMTextBorder()
        Dim ent As AcadEntity
        Dim pnt As Object
        Try
            ThisDrawing.Utility.GetEntity(ent, pnt, "Pick MTEXT to add a border to")
            Dim mt As AcadMText
            mt = ent
            Dim Min As Object, Max As Object
            Dim Coords(7) As Double
            mt.GetBoundingBox(Min, Max)
            Coords(0) = Min(0) - 1
            Coords(1) = Min(1) - 1
            Coords(2) = Max(0) + 1
            Coords(3) = Min(1) - 1
            Coords(4) = Max(0) + 1
            Coords(5) = Max(1) + 1
            Coords(6) = Min(0) - 1
            Coords(7) = Max(1) + 1
            If ThisDrawing.ActiveSpace = AcActiveSpace.acModelSpace Then
                ThisDrawing.ModelSpace.AddLightWeightPolyline(Coords).Closed = True
            Else
                ThisDrawing.PaperSpace.AddLightWeightPolyline(Coords).Closed = True
            End If
        Catch
            ThisDrawing.Utility.Prompt("Invalid Selection")
        End Try
    End Sub

Make sure that your subroutine is declared Public as opposed to Private, so that it will be visible by AutoCAD®. Also, there is one final piece of code we need to add to make this visible by AutoCAD®. We need to add some META data before the subroutine, which tells AutoCAD® that the subroutine is callable directly from AutoCAD®. This is where we assign our subroutine a Command Name for our AutoCAD® Command Line. Add the following code on the line before Public Sub CreateMTextBorder():

	<Autodesk.AutoCAD.Runtime.CommandMethod("MTEXTB")> _

Whatever we put in the brackets will be the command that we type into the AutoCAD® command line.

Our class is now complete, and is ready to be compiled into a DLL file for use with AutoCAD.

Compiling

Under the debug menu, we can select Build to create our .dll, but if we do it now the NETLOAD command in AutoCAD® will fail to load the .dll file. This is because the .dll file must be built on the same version of the .NET framework as the version of AutoCAD® you are using. AutoCAD® 2011 is built on version 3.5 of the .NET framework, so we need to tell VB to compile our class using this version.

  1. Go to project properties as we did before for adding references.
  2. Click on the Compile Tab.
  3. At the bottom, click on Advanced Compile Options.
  4. At the bottom of the Advance Compiler Settings dialog box, select the Target Framework .NET Framework 3.5.
  5. Click OK. This usually requires closing and reopening the project afterwards.

Now we can build our .dll file based on the same .NET Framework as AutoCAD®, which should make it compatable. It is useful to have the Output Window open, so that we can grab the location of the compiled .dll file once the build is complete. You can open this window by going Debug > Windows > Output. Go Debug > Build, and this will compile the .dll file. Copy the path of the .dll file from the Output window, and open AutoCAD.

Type NETLOAD into the command line. This is the command for loading .NET projects. You will be prompted to supply a path, so paste in the path to the .dll file we just created. If it worked, it should silently finish the command, i.e., you shouldn’t get any error messages. Now that the .dll is loaded you should be able to type in the command specified in the META data to call the subroutine inside the .dll, in the case if this example, MTEXTB.


I would like to take this opporunity to suggest that you subscribe to my blog – if you work with AutoCAD® I have many tips and tricks on the tip of my tongue. I guaranteee that you will find it a valuable resource.

VBA in AutoCAD® – Tutorial 2: Subroutines

Introduction

This tutorial assumes that you have read all previous tutorials, but have no other VBA knowledge for AutoCAD® or otherwise.

In this tutorial, I will explain the basics of subroutines.

Subroutines

In the last tutorial, I explained some basic code. The observant of you will have noticed that there were a few parts of the code that I left unexplained:


Sub QuickExample()
End Sub

This is a subroutine. The first line defines the beginning, and the second line defines the end. Similarly to variables (remember those from the last tutorial?), the name can be changed to whatever we like (certain rules apply). However, the subroutine name must end with a pair of parantheses. If they are omitted, they will be added automatically. You may notice after typing a line such as Sub QuickExample and pressing enter, that the End Sub statement is automatically inserted. If any subroutine has no corresponding End Sub, it will not run, and an error will occur.

A subroutine is a container for our code. If we had a subroutine that contains code that converts TEXT to MTEXT, it would be logical to call it something like ConvertText2MText. When we use the command VBARUN from AutoCAD®, we are presented with a dialog box that gives us the option to execute whatever subroutine we like. So in this example, we would pick the option that refers to the ConvertText2MText subroutine.

The above method using VBARUN is how to execute a subroutine directly from AutoCAD®. We can also run the subroutine from within VBA – perhaps from another subroutine. The way to do that, is to write the subroutine name in our code. So to run the subroutine in the example above, we would simply write:

ConvertText2MText

When VB reaches this line of code, it will jump to the line of code that says Sub ConvertText2Mtext(). Then, it will run the content, and when it reaches the End Sub statement, VB will return to where it was originally, and continue to process code as normal. This can be a useful way of splitting up our VBA applications into logical and understandable chunks that can be called upon whenever necessary.

So lets expand on our example. Lets say that we have 4 subroutines. I’ll put 3 of them below:


Sub ConvertText2MText()
    MsgBox "Convert Text to MText"
End Sub

Sub ConvertLines2Polylines()
    MsgBox "Convert lines to polylines"
End Sub

Sub SetupSystemVariables()
    MsgBox "Do setting up of system variables"
End Sub

I’ve omitted the actual code for these subroutines as it isn’t what I’m focusing on. Each of the above could be called directly from AutoCAD® by entering VBARUN into the command line, and then selecting the desired subroutine to run. But if we actually want to run all of them however, it might be useful to set up another subroutine to call them all:


Sub ReformatDrawing()
    MsgBox "Beginning running all subroutines..."
    ConvertText2MText
    ConvertLines2Polylines
    SetupSystemVariables
    MsgBox "Completed!"
End Sub

When you execute the ReformatDrawing subroutine, it will run the other 3 subroutines in the order that they appear. Some of you might say “You could just put all of the code into one subroutine – why not just do that?”. Well yes you could, but when you start making complicated code its not advisable because it makes it hard to follow. Also, programming in this way makes your code nicely reusable because it easy to transfer whole subroutines from one project to another.

More on Subroutines

We’ve covered the purpose, and basic usage of subroutines. Now I will show you what else subroutines can be useful for.

It is sometimes useful for the subroutine to do certain things based on given input. Say for example we wanted a subroutine that inserts some text into the drawing at a changable position. We can make it so that we can give the subroutine some parameters, and make it do things based on the information we provide. In this example, we could make it so that the subroutine will put text into our drawing based on coordinates that we supply. So I will explain how to pass parameters to a subroutine. Here we have a subroutine that inserts text into our drawing (it’s the same as the one in Tutoral 1):


Sub InsertText()

    Dim MyString As String 'Create string variable
    MyString = "Hello! This is the contents of the string variable called MyString" 'set it to something
    MsgBox MyString 'show it in a messagebox

    Dim Point(2) As Double 'This is how to create an array
    Point(0) = 10 'This is x
    Point(1) = 20 'This is y
    Point(2) = 0 'This is z

    Dim TextHeight as double 'Create double precision floating point number variable
    TextHeight = 10 'set textheight to 10

    ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight  'Add text to drawing in modelspace

End Sub

This subroutine is fine, but it’s not very useful because it does the same thing every time! However, if we alter the code slightly, we can make it a bit more intuative. We can alter the subroutine so that it is anticipating additional information. If we do this, we will have to provide the additional information when we call it. To make the subroutine expect additional information, we add contents to the parantheses as follows:


Sub InsertText(MyString as String)

    MsgBox MyString 'show whatever was passed to the subroutine in a messagebox

    Dim Point(2) As Double 'This is how to create an array
    Point(0) = 10 'This is x
    Point(1) = 20 'This is y
    Point(2) = 0 'This is z

    Dim TextHeight as double 'Create double precision floating point number variable
    TextHeight = 10 'set textheight to 10

    ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight  'Add text to drawing in modelspace

End Sub

Now, to call this subroutine we would use something like:
InsertText “Hello! This is some text that I am passing to the subroutine”

This would need to be contained in another subroutine. I’ll rewrite it all so that it makes some sense:


Sub MainSubroutine
    InsertText "Hello! This is some text that I am passing to the subroutine"
End Sub

Sub InsertText(MyString as String)

    MsgBox MyString 'show whatever was passed to the subroutine in a messagebox

    Dim Point(2) As Double 'This is how to create an array
    Point(0) = 10 'This is x
    Point(1) = 20 'This is y
    Point(2) = 0 'This is z

    Dim TextHeight as double 'Create double precision floating point number variable
    TextHeight = 10 'set textheight to 10

    ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight  'Add text to drawing in modelspace

End Sub

If we input VBARUN into the command line, and select MainSubroutine, we should get exactly the same scenario as we did to begin with. However, it happens differently. This time, we are running the subroutine called MainSubroutine, this is in turn calling the subroutine InsertText, and is providing that subroutine with some text. When VB jumps to the InsertText subroutine, it creates a variable called MyString, and automatically stores the text in here. Notice that I have removed some of the code inside the new sub – it no longer needs to create the MyString variable (with the Dim statement), or set the text in that variable, because it now happens automatically as part of the call to the subroutine.

This is a simple example using one parameter. At the moment this doesn’t really add any more functionality, but we can add more parameters as follows:


Sub MainSubroutine
    InsertText "This is the first call to the InsertText Sub", 10, 20, 0, 10
    InsertText "This is call number 2!", 10, 40, 0, 10
    InsertText "This is the third and final call", 10, 60, 0, 10
End Sub

Sub InsertText(MyString as String, XCoordinate as Double, YCoordinate as Double, ZCoordinate as Double, TextHeight as Double)

    Dim Point(2) As Double 'This is how to create an array
    Point(0) = XCoordinate 'Set the contents of Point(0) to whatever is stored in the variable XCoordinate
    Point(1) = YCoordinate 'Set the contents of Point(1) to whatever is stored in the variable YCoordinate
    Point(2) = ZCoordinate 'Set the contents of Point(2) to whatever is stored in the variable ZCoordinate

    ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight  'Add text to drawing in modelspace

End Sub

Now we’ve set up the InsertText subroutine so that it accepts parameters for the contents of the text, the location, and height. This is more useful from a programming point of view because we can now insert some text into the drawing at any position, any height, and containing whatever contents we like; all only using one line of code as shown in the MainSubroutine.


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VBA in AutoCAD® – Tutorial 1: Introduction

Introduction

Knowing a little bit of programming can be extremely useful in the AutoCAD® environment. Before you cringe with dread at the prospect of having to learn a programming language, it sounds far more difficult than it really is. Especially since VB stands for “Visual Basic” – there’s a clue in the name… Writing simple applications for automating tasks isn’t hard – really.

This tutorial assumes no previous knowledge of VBA in AutoCAD® or otherwise. I will explain the very basics of using VBA in AutoCAD®. I will give a brief overview of the VBA IDE (Integrated Development Environment) and I will explain a small snippet of code and how it works.

What is VBA?

If I assume you know nothing about VBA, it follows that you probably don’t know what VBA stands for. VBA stands for Visual Basic for Applications. Most people reading this will probably have heard of Visual Basic, and are aware that it is a Microsoft Windows based programming language. The “for Applications” bit means that it is integrated behind the scenes in the software application you’re using, be it Word, Excel, or in our case AutoCAD.

Step One – Familiarise with the IDE

In order to begin, we need to access the VBA IDE. This is where we will be working. Input VBAIDE into the command line. This opens up a new window which is the VBA IDE. You should have something that looks like the below:

The section of the screen with the big red “1” is the project window. This shows you all the sections of your VBA project. Right click in this area and select insert/module. This will (surprisingly!) insert a module. A module is basically a container for your code. If you like, you can rename the module from “Module1” to something more descriptive of what the module does or is for.

The section of the screen represented by the number 2 is the properties window. Various aspects of your project have certain properties that can be edited. I won’t go into this right now.

The section of the screen represented by the number 3 is the editing window. If it’s grey at the moment (like in the example), you’re not editing anything. If you’ve added a module, chances are you’re looking at a white screen, and you can type stuff. When you add a module, it automatically opens it up in the editing portion of the screen.

The section of the screen represented by the number 4 is a toolbar – in particular the buttons that handle the execution of code. The run button causes VBA to start executing code from the current subroutine (i.e. the subroutine in the module you’re editing that contains the cursor). The pause button will pause execution, and take you to the debugging screen. The current position that VBA has got to will be highlighted with yellow. The stop button halts execution.

Step Two – Add some code, and run it

Make sure you’re at a state where you are editing a module. You might have at the top of the screen the words “Option Explicit”. This is fine, but also don’t worry if it’s not there. You don’t really need to know about this right now. Paste the following code into the module:

Sub QuickExample()
    Dim MyString As String 'Create string variable
    MyString = "Hello! This is the contents of the string variable called MyString" 'set it to something
    MsgBox MyString 'show it in a messagebox
    Dim Point(2) As Double 'This is how to create an array
    Point(0) = 10 'This is x
    Point(1) = 20 'This is y
    Point(2) = 0 'This is z
    Dim TextHeight as double 'Create double precision floating point number variable
    TextHeight = 10 'set textheight to 10
    ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight 'Add text to drawing in modelspace
End Sub

Everything should have pasted in nicely. The text should automatically change into a lovely assortment of black, dark blue, and green colours. If you get any red, then something went wrong when you copy and pasted. When editing code, different colours of text represent different things. Green text represents a comment or note – this text can be anything and is for the purpose of you making your own notes. Dark blue text represents key words that VB understands. Red text indicates anything that contains errors, or the structure of what you’ve written is wrong. However, just because it’s not red, doesn’t necessarily mean that it contains no errors. Black is anything that doesn’t fall under any of the above.

You probably guessed that to execute the code, you click the run button in the toolbar at the top. The shortcut for this button is the F5 key. As an additional point, it is sometimes useful to know how to execute your code without opening the IDE. To do this, you would type in -VBARUN into the command line, followed by you’re subroutine name. This command can conveniently be stored in a toolbar or pallette using the normal process for editing the user interface – CUI. Notice the preceeding “-” in front of the VBARUN command. You probably already know this is an AutoCAD® command modifier. The dash explicitly tells AutoCAD® to expect command line entry. If the dash is omitted, VBARUN opens a little dialog box, and you can pick your subroutine from there.

Step Three – Understanding the code

Maybe you executed the code and thought “that’s not very interesting..”. If so, I assure you this is the tip of a very large iceberg. In the code above, I’ve added comments in such a way that it explains it a little, but I’ll give a little more detail now.

Code is executed from the top down in the same manner you would read a book, unless you tell VB to do something else.

Dim MyString As String

This is the first line of code. This line creates what is known as a variable. The Keyword “Dim” is the part of the code that tells VB to create a variable. A variable is basically a memory bank with a name. The name of the “memory bank” or variable is MyString. We specified the name MyString, but it could have been called something else if we liked. The line Dim This_is_a_variable as string would be equally valid, but it’s a bit of a mouthful. Also, any reference to MyString in the code would need to be changed to This_is_a_variable in order for the code to work in the same way. The part of the code that says “As String” tells VB what type of variable it is. In this case, it is what is known as a String variable, or a Text-String. This basically means that anything that is attempted to be stored into the variable MyString should be interepretted as Text. If it is not text, VB will try to convert it to text. If it cannot, an error will occur with the message “Type Mismatch”

MyString = "Hello! This is text in a string variable!"

This line of code shows you how to set the contents of a variable. It is simply a case of stating that Variable = SOMETHING. The text after the equals sign must be enclosed inside quotation marks. If it was not enclosed in quotation marks, VB would try to execute the text as code, and an error would occur (the text would also be red). So enclosing it in quotation marks tells VB not to interpret this as code, but use it as a text value.

MsgBox MyString

This line of code causes a messagebox to be displayed. The command for doing so is MsgBox. The part following MsgBox in this instance is our variable called MyString, however we didn’t have to use a variable here. We could have explicitly put in any text we like enclosed in quotation marks, and it would be executed in the same way, displaying the inside of the quotation marks instead of the contents of the variable.

Dim Point(2) As Double

This should look quite familiar – again we’re declaring a variable. You’ll notice that it is a different type. In this instance it is a number. Specifically, a double precision floating point number, but we don’t need to know the details yet. You might also have noticed the brackets containing the number 2. The name of the variable is still just Point but this time it is an array. Think of an array as a list within that variable. This particular array has 3 elements to that list – 0, 1, and 2. We’ll probably talk more about arrays at another time.

Point(0) = 10 'This is x
Point(1) = 20 'This is y
Point(2) = 0 'This is z

Similarly to before, this is assigning values to the variable. However this time, as we’re dealing with an array, we need to specify which part of the list we want to assign our value to. Realise that all of the values are actually stored in the same variable, but just organised into a list.

Dim TextHeight As Double
TextHeight = 10

No problems here.

ThisDrawing.ModelSpace.AddText MyString, Point, TextHeight

The final line of code in this subroutine. The first part is quite self explanatory – Thisdrawing.Modelspace.Addtext. This adds some text into the modelspace of the active drawing. If there is no active drawing (i.e, they’re all closed) an error will occur. In order for AutoCAD® to be able to add text, it needs to know certain things: What text do you want to display? Where do you want to display it? What size do you want it to be? At this stage I will point out that the text we are adding is NOT MText. It is Text – what you would get by using the Text command in AutoCAD®. Conveniently, we’ve already set up some variables that contain the values we need. Pop them after Thisdrawing.Modelspace.Addtext in the right order, delimited with a comma, and you’ve now got some text in the modelspace of the current drawing.


I hope you found this a useful introduction – we haven’t don’t anything particularly useful yet, but there’s much much more great info where this came from. If you liked what you read I would encourage a subscription – you won’t regret it!

The CIRCLE command and the circle entity

The circle is one of those commands that can be very useful in the hands of those that know how. Obviously if you want to draw a circle this is what you need – but beyond that, circles have useful properties that make them very useful when trying to draw certain things. We’ll see some examples of what I mean later on in this post.

Normal Usage

 Invoke the CIRCLE command, and you will be prompted to supply a centre point for the circle. Next, you will be prompted for a radius. Simple.

There are some useful other ways to define your circle. One that is sometimes particularly useful is the TTR option, which is for drawing a circle of a given radius that is at tangents to two other objects.

Other Usage

One very useful little tactic sometimes is where you need to space out items, whatever that item may be, along a path. There are other ways of achieving this, but I find the circle method to be quite elegant and quick.

Draw a circle with your desired spacing as the radius. Begin the COPY command selecting the circle as your object to copy, and pick the centre point of the circle as your copy base point. Then, you can select the intersection between the circle and the path line as your insertion point for your new circle. Cunningly, we’re still in the middle of the copy command, and we have a new intersection to snap to as a result of the new circle we just created… snap to that intersection… then the next one… you get the idea. The notion using the COPY command in this sort of iterative way is very useful and will be discussed in greater detail when I write a post about the COPY command.

The BOUNDARY command

The BOUNDARY command is one of those tools that is mostly unknown and seldom gets used… which is a shame because it can be really useful. The BOUNDARY command draws a polyline by taking a point from the user, and looking for the boundary that encloses it. In other words, it returns the boundary that would be found if you used the “pick points” option from the HATCH command.

Normal Usage

Invoke the BOUNDARY command and you will get a little dialog box. You can choose to untick “Island detection”, and you can change the object type that is generated from polyline to region. Once this is set up click “Pick Points” at the top, and select a point on screen that is enclosed by other objects. As you’d expect objects that are hidden or frozen are not considered in the formation of a valid boundary.

Special Usage

One of the most intuative ways of using this tool is to retrieve the boundary of complex shapes. Consider the below arbitrary set of shapes:

If you wanted to convert this into a polyline boundary, how would you do it? A lot of people would just head directly to the TRIM command and start hacking away. The more AutoCAD® savvy person might take another approach… You probably gathered as you’re on the BOUNDARY page, that this can be achieved using the BOUNDARY command, but have you figured out how? How about when you consider this:

By using another boundary around the objects, you can pick a point in the area between the outer boundary and the set of shapes, and capture the outline of the complex shape as an island. Once you have your outline, just delete the bits you don’t want. This can be an extremely useful trick for very complex shapes, and can save a heck of a lot of time and effort.

The RECTANG command

The RECTANG command draws a rectangle (surprisingly..), which is really just a closed polyline. There are however a few ways you can use the command that you may not know about.

Normal Usage

Invoke the RECTANG command, and pick two points denoting the two opposing corners of the rectangle. It might be worth noting that the polyline is drawn starting from the first point you specify, in the horizontal direction. So if you specify the bottom left followed by the top right, it will be drawn in the anti-clockwise direction.

Special Usage

Perhaps the most interesting usage is the ability to add chamfers and fillets to the rectangle. This could be quite handy in some circumstances. Otherwise this tool is pretty straight forward.

Other Information

There is some best practice advice I can give on the use of rectangles (and any other polyline). Generally you want to use them in a way that makes sense in the context of the drawing. For example:

This is a washer drawn in section – so the rectangle in the middle represents the hole through the centre of the washer. However, none of the rectangles that I drew enclose the centre rectangle. Instead, the washer is made up from one rectangle on the left, one on the right, and one denoting the boundary:

If you think about it this makes much more sense than anything else because you’ve captured the actual outlines of the object. These can be reused later in a way that makes sense, i.e., as a hatch boundary in this example. Try to get in the habit of thinking in this way and you’ll save yourself time later.

There is much more good advice from where this came from – please do subscribe to my blog.

The PLINE command and the polyline entity

The PLINE command creates an entity known as the polyline, which is basically a series of connected lines or arcs. There are some interesting tips for using polylines and the PLINE command, and many system variables that govern its use. There are also a few ways that you can customise AutoCAD® to utilise the polyline to better advantage.

Normal Usage

After invoking the PLINE command the user can pick points to define the path. The ‘A’ key can be pressed to switch to arc mode whereby arcs are created instead or lines. There are several modifiers once in arc mode, such as pressing ‘D’ to reorient the start direction of the arc.

Types of Polyline

Confusingly there are three types of polyline – polylines, 3D polylines and LW polylines (light weight polylines). The difference between them is that a LW polyline truly is two dimensional – it only stores X and Y coordinates, but it must be associated with a UCS plane. When drawing a LW polyline it inherits the current UCS as the plane for that LW polyline. Points added must reside on this plane, which can sometimes cause confusion when there is also three dimensional data in the drawing.

You don’t get any points for guessing what a 3D polyline is I’m afraid… Yes, it captures the coordinates in three dimensional space rather than on a two dimensional plane. This one isn’t creatable using the PLINE command – it has a command of it’s own called 3DPOLY.

So what is the last type… the one that isn’t a LW polyline or a 3D polyline… the one simply called a “polyline”? It is the type of polyline that was originally available before AutoCAD® R14. It too captures all the three dimensional coordinates for every point, so in this sense it is the same as the 3D polyline, but this type only allows 2D geometry. You can only draw shapes that would be possible to draw on a two dimensional plane. So in terms of what you can do with it, its the same as the LW polyline. It does the same job, just much less efficiently, hence why the newer version is called a light weight polyline. It is only really provided for backwards compatability and generally it is use is depreciated.

This brings me on to my next point – what type of polyline is created by the PLINE command? This is controlled by the system variable PLINETYPE. By default PLINETYPE is set to 2, which tells AutoCAD® to use LW polylines instead of polylines. Additionally, all old format polylines are automatically upgraded to LW polylines when the drawing is opened. You can change this setting to 0 or 1 to stop AutoCAD® upgrading polylines and to force AutoCAD® to produce old-format polylines from the PLINE command, but I’d strongly advise against it.

Special Usage

Polylines are versatile little things, and I’d recommend using them instead of lines in pretty much all cases. In addition to being able to have a line-thickness property much like any other entity, polylines are given the option of a width too. Most AutoCAD® users don’t realise that polylines can vary in width along the length of the line. Polylines do not have to be a uniform width. The global width option under properties is what people tend to go to when they want to change polyline width which is perhaps where the perception comes from. But all this does is override all width properties along the whole line. You can specify individual widths at any segment of the polyline by iterating through the points of the polyline in the properties window. This allows you to edit the start and end widths of the segment. This can be done on the fly when creating the polyline using the ‘width’ option during the command.

Because of their continuous nature, polylines make excellent boundaries for specifying a hatch boundary. I’m sure nearly every person that has ever used AutoCAD® has selected the ‘pick points’ option under the HATCH command, only to receive the message “a closed boundary could not be determined”. Infuriating as this can sometimes be, it is usually due to a gap or ambiguity somewhere in boundary. Get into the habit of drawing your objects using polylines and this will become less of an issue. Your boundaries for hatching will already be defined – you’ll just have to use the ‘select objects’ option instead.

Other Information

Third party software can sometimes generate polylines in the ways that we do not expect. For instance, have you ever had a polyline that you just couldn’t join other lines to? This is usually down to one of two things: the UCS of the polyline, or its elevation. Sometimes you can get polylines where the UCS is looking in a completely different direction, even though the drawing is say in plan. There is a quick fix for this however, simply explode the polyline to convert it into its constituent parts, and rejoin them into a polyline in the UCS you want. This may require also selecting all of the exploded lines and changing their Z coordinate to 0. The second common reason for polylines that won’t join is due to elevation. Make sure that the elevation of the polyline and what you’re joining it to is what you expect, and this should then allow you to join them.

Editing Polylines

The PEDIT command allows you to edit polylines. This is a useful feature, expecially when used on objects that aren’t polylines in the first place. This will convert the entity to a polyline, however there is a somewhat annoying popup asking you to confirm the action. Fortunately as with most things in AutoCAD®, this can be customised. Set the PEDITACCEPT system variable to 1 to suppress this prompt.

There is also an extension to this idea which I personally like to use. A little known trick is that under the CUI editor, users can customise the default double click action on specific entities. The default action when double clicking on a line for example, is to open the properties palette. Try changing the default action of lines and arcs to the PEDIT command instead, and you will be able to convert to polylines with a simple double click.

Some users may experience the problem of linetypes being irregular along polylines. This problem is caused by a display property of the polyline, namely the ‘linetype generation’ property. This should be set to ‘enabled’. The default property when polylines are created can be customised with the PLINEGEN.


There are many other commands that produce polylines as their ultimate output, including RECT, BOUNDARY, POLYGON, DONUT, and SKETCH.

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The LINE command and the line entity

It doesn’t get much simpler than this does it. Does it…?

Well, no not really. But there are a few things that people generally don’t know, and there are some misconceptions about the LINE command that you should know about.

Normal Usage

After starting the LINE command you are prompted for a start point and an end point. Enter them as requested, and you’ve got yourself a swanky new line in your drawing. The LINE command repeats until cancelled by the user, assuming the end point of the last line is to be the start point of the new line. During a chain of lines you have the option to press ‘U’ for undo, which deletes the last line drawn, or ‘C’, which ends the command by joining the ends of the string of lines to form a closed loop.

Special Usage

Did you know that you do not have to give a start point? This is a fairly standard AutoCAD® thing, but if you press return at the prompt AutoCAD® will assume you want to start from the last point you entered. So if you drew some lines, ended the command but then wanted to continue drawing from the endpoint of the last line you drew, start the LINE command and press return at the first point prompt.

Ok its not that special, but it leads me to the extension of this idea. Lets assume the last object you drew was an ARC. If you now invoke the LINE command and press return at the first prompt, the start point is at the end point of the ARC, as you’d expect. But, the line is constrained to the tangent of the ARC, which could indeed be quite useful.

Other Information

There is often debate on whether it is better to by default use the LINE command or the PLINE command. The PLINE command offers additional functionality but at the cost of file size. I want to dispel the notion that polylines result in bigger file sizes, because it simply is not true. Yes, if you compare one polyline with one line, the polyline contains more information and therefore takes up more space. But, compare a string of lines to the same string of lines represented by a single polyline and you’ll get a different story. The reason for this is that a polyline stores the points as a list of coordinates. While its true that lines do the same, a string of lines means that there are many repeated coordinates because the ends of the lines are on top of each other. So in this instance the overhead of having a polyline is worthwhile because it stores the points more efficiently.

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