The Key to Standardizing Annotation in CAD Files - Part 2: Linetypes

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T


his month’s column is the second in a series covering the different aspects of CAD standardization regarding annotation. The first, “The Key to Standardizing Annotation in CAD Files,” explains how to standardize text; it appears in the June 2011 issue of this magazine.

The good news is that working with linetypes in AutoCAD or IntelliCAD is much, much easier than working with text. Unlike text, the size of dashes, gaps, text, or shapes that define a linetype can be updated easily as the drawing scale changes by using the LTSCALE system variable.
 

How Linetypes Are Defined

Before I discuss that, let’s start with the very basics of linetype definitions. In AutoCAD-based programs, linetypes are defined in a file called acad.lin. Likewise, IntelliCAD’s linetype definition file is icad.lin. You can usually find the .lin files in one of the support folders in the program installation folder.

The .lin file is a text file that can be opened and edited in a text editor such as Notepad. The file is separated into four sections: Standard Linetypes, ISO Linetypes (Metric), Complex Linetypes, and User-defined Linetypes.

A sample of the acad.lin file is shown in Figure 1 with a few of the Standard Linetypes highlighted.

Using the DASHED2 Linetype as an example, let’s look closely at the different parameters of the definition:
DASHED2
This is the name of the linetype.
 
Dashed(. 5x)_ _ _ _ _ _ _

This is a description and sample of the linetype.

A

The letter “A” represents the type of Alignment and simply means that, when applied to a line or arc segment, the pattern will start and end with a dash segment (as opposed to a gap). An “A” Alignment is the only type supported in AutoCAD or IntelliCAD.

.25

This represents the length (when plotted at 1:1) of the first dash in the linetype. This setting gives away just how long AutoCAD has been using the acad.lin file. To draw a dash, a positive number in this field translates to “pen-down”—a shout-out to old pen-plotters!

-.125

This represents the length (when plotted at 1:1) of the first gap in the linetype. Like mentioned above, a negative number in this field used to tell pen-plotters “pen-up,” creating a gap in the linetype.

The standard AutoCAD or IntelliCAD linetype definitions come in groups of three, such as DASHED, DASHED2, and DASHEDX2. In each of these cases, the “2” version of the linetype has dashes and gaps that are one-half the length of those in the original version of the linetype. The “X2” version has dashes and gaps that are two times the length of those in the original.

Tip: If you have a template drawing (.dwt) file or other drawing that you use to start your new drawings, don’t forget to set your PLINEGEN variable to 1 (ON). This allows polylines to evenly distribute a linetype pattern from the start to the end of the polyline rather than between vertices. In Figure 2, the image on the left shows contour polylines with PLINEGEN set to 0 (OFF) and the one on the right with the variable set to 1 (ON).
 
Looking a little further down in the acad.lin file, you see a section titled Complex Linetypes (Figure 3). Two of the Complex Linetypes provided in the acad.lin file contain text strings: HOT_WATER_SUPPLY and GAS_LINE. Looking closely at these definitions you can see that the only difference between these linetypes and the standard linetypes at the top of the file is the inclusion of the formatting instructions for the text string included in brackets.

Let’s use the GAS_LINE linetype to look at the different parts of the definition:
 
HOT_WATER_SUPPLY
This is the name of the linetype
 
Hot water supply ---- HW ---- HW ---- HW ----
This is a description and sample of the linetype.

A
The letter “A” represents the type of Alignment.

.5
This is the length of the first dash.

-.2
This is the length of the gap on the left side of the text to be inserted.
 
“HW”
This is the text that’s to be inserted into the linetype.
 
STANDARD
This is the text style to be used.
 
S=.1
This is the size of the text (when plotted at 1:1).
 
R=0.0
This sets the rotation angle of the text in relation to the line segment to 0 degrees.
 
X=-0.1
This is the distance, in the x direction, that the text is to be shifted to properly position the text between the two adjacent dashes.
 
Y=-.05
This is the distance, in the y direction, that the text is to be shifted to properly position the text between the two adjacent dashes.
 
-.2
This is the length of the gap on the right side of the text.
 
Tip: The Rotation parameter forces the text to align with the line regardless of the direction it’s drawn. This can be problematic with text in a linetype because lines drawn from left to right will produce text that is upright, but a line drawn from right to left will have text that is upside down.

Instead of the “R” (Rotation) we can use a “U” (Upright) flag. The “U” flag keeps the text upright in the drawing regardless of the direction the line was drawn. Just insert “U=0.0” in place of the “R=0.0” to generate this result.

The polyline in Figure 4 was drawn from the upper left to the lower right and then to the lower left. The picture on the left shows the linetype when the Rotation flag is used and the one on the right uses the Upright flag.
 

Adjusting Linetypes for the Scale of a Drawing

As mentioned previously, linetype definitions are based on a 1:1 scale or the desired plotted length of dashes and gaps. Obviously, when we are working with boundary lines that are hundreds of feet long, dashes and gaps of 0.5 or 0.25 feet will not be visible. This is why we change the LTSCALE environment variable. The default LTSCALE is 1, and it applies to both Model and Paper Space. It can be changed at any time and is effective immediately. When displaying a linetype in a drawing, all of the parameters of a linetype definition are multiplied by the LTSCALE to determine the actual length of dashes and gaps.

So, when the LTSCALE is set to 1, the length of dashes and gaps exactly matches the values specified in the linetype definition. But, once the plot scale of the drawing has been decided, the most commonly accepted practice is to set the LTSCALE to match the plot scale. So, lines having a DASHED2 linetype in a 40-scale drawing with the LTSCALE set to 40 will have dashes that measure 20.0’ long and gaps that measure 10.0’ long.

Tip:  If you insert your title blocks into Paper Space at 1:1 and then scale the viewport to the plotted scale, you will probably notice that your linetypes appear to be Continuous in the viewport. You will need to toggle another environment variable, PSLTSCALE, from 1 (ON) to 0 (OFF) to display and plot linetypes properly.

Tip: If you have more than one Viewport in your Layout Tab and the Viewports have been scaled to different scales, set the LTSCALE to 1 and the PSLTSCALE in Paper Space to 1 (ON) to have the linetypes in both viewports appear and plot properly.


 

About the Author

  • Jennifer DiBona
    Jennifer DiBona is an independent consultant doing business as That CAD Girl. She is a Carlson Software reseller and provides CAD training, technical support, and other CAD-related services. Visit her website at www.thatcadgirl.com to find out more.

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