Cadtales

Complex Linetypes

by Jim Rogers, CADreps

Fun with Complex Linetypes was the working title for this lesson. To the novice or the un-trained AutoCAD user complex linetypes are a bit confusing and probably not fun. To help you understand and benefit from complex linetypes we’ll break down the simple but cryptic code for creating these useful objects so your drawings can present clear and comprehensive information with these symbolic lines.

To introduce this subject we’ll review the basic properties that make up a linetype, look at the “code” that generates the line, and analyze each component and its impact on the resulting line. Standard linetype descriptions are stored in the acad.lin file. You can add your custom linetypes to this file or create your own “.lin” file (See the Exercise at the end of this lesson). To find the location of the acad.lin file, open the Properties Tool Bar, Linetype list arrow and click “Other.” In the Linetype Manager dialog box click the Load button. In the Load or Reload Linetypes dialog box note that acad.lin is posted and highlighted in the file selection window. Click the File button and note the directory path to this file. The default path is C:\Documents and Settings\”user name”\Application Data\Autodesk\AutoCAD 2008\enu\support. This file can be opened and edited with Notepad or any similar non-formatting editor. Always make a backup copy before editing.

Figure 1, below, shows a sample of the Hidden linetype, with dimension labels indicating the length of the line segment and the space that follows. Note that all linetypes are created with fixed elements with specific dimensions, then, scaled up or down to make them useful for micro to macro drawings. We’ll explore the scaling tools LTSCALE, CELTSCALE and PSLTSCALE later in this lesson.

Figure 1

The start of the linetype descriptor is marked with an asterisk “*”. “HIDDEN” is the technical name of the linetype and is separated from the common name (Hidden) by a comma. The “graphic” information that follows is a proxy representation of the linetype created with common keyboard text characters: dashes, hyphens, plus signs, parentheses, etc.

The second line contains the instructions AutoCAD will use in creating the linetype on screen. A comma “,” separates each command element, and each line in the instruction set must end with a carriage return (Enter key).

A stands for A-type alignment,
.25 is the length of the line segment in AutoCAD Units,
- indicates a space, and
.125 is the length of the space in AutoCAD Units. (Enter)

The line command will automatically repeat the above pattern to fill the space between the two points picked on the screen by the operator and, add the beginning line segment to the end to form a completed line.

Figure 2

Figure 2 shows two companion linetypes for comparison. Note that Hidden (.5x) and Hidden (2x) differ from the original line type only in the length of the line and space segments. These linetypes are “pre-scaled” to accommodate a range of common scale factors (1/16”, 1/8” and 1/4”) quickly and without changing related drawing properties.

For our second example we’ll use the DHWC linetype used to draw domestic hot water lines (pipes) in schematic drawings. See Figure 3 below.

Figure 3

The English translation for this linetype sequence is:

A is for A-type alignment,
.75 is the length of the first line segment (all lengths in AutoCAD Units),
-0.25 space,
0.25” line,
-0.25 space,
0.25” line,
-0.25 space,
0.25” line,
-0.25 space (Enter)

Simple Customizations - Creating a custom linetype is easy. Open the acad.lin file with Notepad. Copy an existing linetype to the clipboard (Ctrl+C), scroll down to the User Defined section and paste the copy into the list. Change the name and description in the first line, then, change the line and space instructions in the second line to provide the desired pattern. (Be sure you have an Enter key at the end of each line). Save the file and Load the new linetype. In the event of an error in the new, or any other linetype, the Load function will give you an error message and list the linetype name, the type of error and the line number in the file.

Complex Linetypes with Shapes - Starting with any basic linetype we can add additional visual content and information by adding text and shapes. The Tracks and Batting linetypes are two examples that utilize the ltypeshp.shx file to create illustrative patterns for rail road tracks and wall insulation batting. (The location of the SHP or SHX file must be set in the support path. Use the instructions in the AutoCAD Customization Guide under “Linetype Definition Files.” Customizing with shapes will not be covered in this lesson).

Figure 4 lists the instructions for these linetypes and Figure 5 shows the lines as created in AutoCAD.

Figure 4

Figure 5

Complex Linetypes with Text - The Hot_Water_Supply and Gas_Line linetypes are two examples that utilize text to add information and convey meaning to a line and, save time by avoiding other labeling methods. See Figure 6 for the linetype instructions and Figure 7 for the lines as created in AutoCAD.

Figure 6

Figure 7

Follow the instructions in the Simple Customizations section above to create simple linetypes with text. Change the name & description and substitute your own letter(s) into the “HW” or “GAS” text string, keeping the letter count the same and retaining the quotation marks.

Complex linetypes with text contain two essential elements: 1) Line & space descriptors and, 2) A Text Style reference with height & offset transform. The “complex” part of the linetype description is contained within the square brackets, i.e. [“GAS”,STANDARD,S=.1,R=0,X=-.1,Y=-.05].

Where:

[ ] Brackets enclose the string, stylename, and transform
“GAS” is the text string, including the quotation marks,
STANDARD is the text style,
S=.1 is the height of the text in this case, or scale of height set in the text style,
R=0.0 is the rotation, set to zero relative (to the line) rotation,
     (Replace R=0 with A=0 to set the absolute angle of the text).
X=-.1 is the x-offset, set to -.1 units, (-.1 shifts the text to the left)
Y=-.05 is the y-offset, set to -.05 units. (-.05 shifts the text down)
     (X and Y are +/- values, not spaces)

Note: The -.25 parameter (following the brackets) is the area between the dashes and spaces reserved for the text. The only difference between the HW and GAS instructions in Figure 7 are the ending text-space numbers, -.2 vs. -.25, allowing for more, or less, letters. Each element in the instruction set is separated by a comma and there are no spaces. And, remember – each line must end with an Enter key.

The graphic in Figure 8 is labeled with the applicable linetype definition parameters. The dimensions and text labels have been applied to the second and subsequent instances of lines, spaces and text to avoid the distortion caused by the line command automatically extending the beginning and ending line segments to fill to bridge the two points picked on the screen.

Figure 8

It’s a little strange to this writer that Autodesk would use the STANDARD text style for this and other complex linetypes featuring text because it is the one most often changed by users (through lack of understanding or simply in a hurry). The best policy is to always leave ALL standard styles at their default settings. Create one or more text styles to be used exclusively with linetype definitions. For a new linetype creation, start with the txt.shx font and set text height to zero. This will insure that the “S” transform is the actual text height and not a scale factor of the text height set in the Text Style. Also, be aware that some fonts adhere to standards which may cause the center to be off. After a new complex linetype is working properly you can change to other fonts as desired – making adjusts to the transform parameters as necessary. If in doubt, create the desired text at actual height with Mtext and use the Distance command to obtain measurements.

In the examples in Figure 7 the “HW” and “GAS” text strings are centered vertically in the line regardless of the line’s orientation. The location of the text is controlled by the relationship between: S, the text height; X, the x-offset; Y, the y-offset and the -.25 space parameter at the end of the instruction set. In these examples the y-offset is ½ the text height, the x-offset is equal to the leading space and, the reserved text space (-.25) is approximately equal to the space occupied by the (3) letters.

As noted in the first paragraph, all linetypes other than “continuous” have line and space segments that are created to specific dimensions. In order to use, and see, these line segments on drawings scaled larger, or smaller, than the nominal size of the linetype we apply a scaling factor. The global scaling variable for linetypes is ltscale. The default value is 1. This setting will yield the following visibility characteristics:

Model Space:  

Lines will appear normal in a nominal drawing,
Lines may appear continuous in a larger drawing, and
Lines may appear continuous or not at all in a smaller drawing.

Paperspace:

Lines will appear normal in all drawings and will plot correctly.

For visibility in Model Space, the ltscale system variable can be set manually to match the relative scale at which the drawing will be viewed and printed in paper space. For a drawing scale of 1/8” = 1’-0” use an ltscale factor of 96. (There are 96 1/8’s of an inch in a foot). For a drawing scale of 1/4” = 1’-0” use an ltscale factor of 48. Other drawing scaling factors can be calculated in the same manner. In later versions of AutoCAD the plotting routine will ignore the ltscale setting and plot the lines normally.

A wise operator will avoid confusion and visibility issues by setting linetypes “By layer,” and ltscale to 1. In Model Space we can ignore the appearance of the line and trust that if it’s on the correct layer it is correct and will print correctly.

LTSCALE

LTSCALE is the Global Scale Factor (system variable) value which changes the linetype scale globally for both new and existing objects. ltscale factors <1 make line segments smaller. ltscale factors >1 make line segments larger. The default setting is 1.

CELTSCALE

CELTSCALE is the Current Object Scale (system variable) value controls the linetype scale for new objects. The celtscale value is a scaling factor applied to the current ltscale value. The default setting is 1.

PSLTSCALE

0 = No special linetype scaling. Linetype dash lengths are based on the drawing units of the space (model or paper) in which the objects were created and scaled by the global LTSCALE factor.

1 = Viewport scaling governs linetype scaling. If TILEMODE is set to 0, dash lengths are based on paper space drawing units, even for objects in model space. In this mode, viewports can have varying magnifications, yet display linetypes identically. For a specific linetype, the dash lengths of a line in a viewport are the same as the dash lengths of a line in paper space. You can still control the dash lengths with ltscale.

When you change PSLTSCALE or use a command such as ZOOM with psltscale set to 1, objects in viewports are not automatically regenerated with the new linetype scale. Use the REGEN or REGENALL command to update the linetype scales in each viewport.

EXERCISE

Create a custom linetype named SANDBAG. When creating complex linetypes use the “S” transform to assign the actual text height (text height in the Text Style set to “0”). The linetype transform values for S=(text height) and Y=(y-offset) are used to vertically position the text in the line. The “X” transform can be used to shift the text left (-) or right (+). To center the text vertically Y should equal S/2.

1. In AutoCAD, create a new Text Style: LTtxt.

a. Use the txt.shx font and set the text height to zero.

b. Accept the defaults for all the other settings.

2. Enter ltscale on the command line and set the value to 1.
3. Enter celtscale on the command line and set the value to 1.
4. Enter psltscale on the command line and set the value to 1.
5. In a text editor (Notepad) create a file named Mylines.lin and enter the following text:

*SANDBAG,---- SANDBAG ----
A,1.0,-0.1,[“SANDBAG”,LTtxt,S=0.1,R=0,X=0,Y=.05],-.77 (See note c)

6. Save the file.

Notes: