Cadtales

Complex Linetypes II

How to create complex linetypes
that comply with National CAD Standards

By guest author: Mark McDonough, CAD Systems Manager, Sasaki Associates

Among the most pervasive problems thwarting successful DWG file sharing is that of missing shape files, those pesky little .shx files that people like to use but frequently forget to include with their file transmittal. We need to understand a little bit about shape files if we are to consider using them in complex linetypes. Somewhat confusing is the fact that AutoCAD .shx files can be one of three things: the familiar vector-based AutoCAD fonts; bigfonts (extended font sets, such as Asian language characters); and, shape files containing one or more symbols frequently used when defining complex linetypes. AutoCAD ships with two shape file libraries of its own, Ltypeshp.shx and Gdt.shx, found in the support folder where AutoCAD is installed. To see what's inside the compiled .shx file, find and open the source file that has a .shp file extension. Shown below is the content of Ltypeshp.shp where six shapes are defined.

From within AutoCAD's linetype library file ACAD.LIN, here is the ZIGZAG linetype definition which references the ZIG shape within the Ltypeshp.shx file. Since Ltypeshp.shx is a standard AutoCAD program file, defining linetypes using those shapes does not pose much of a hazard to recipients of your drawings. However, if you create your own shape file library and use it to define custom complex linetypes, you have created an critical file dependency, and the shape files must be transmitted along with any DWG files that reference them.

So what happens when you open a file and one or more SHX files are missing? If the SHX is a font, one can easily substitute a different font. If the SHX is a bigfont, then it's a problem because substituting a different bigfont (AutoCAD ships with several bigfonts) is like substituting apples for oranges. If the SHX is a shape file, then it becomes a serious problem which can make drawings difficult and time consuming to open and, sometimes resulting in file corruption. In my experience (supporting a large CAD user base of over 200) we frequently encounter land survey drawings where SHX shape files are missing - resulting in DWG files that are agonizingly slow to open - taking up to 20 minutes or more to open. The reason for the slowness - AutoCAD is looking, over and over again, for perhaps thousands of instances of shapes used to describe the linework.

The challenge remains, how do we define useful complex linetypes in our drawings, yet mitigate the risk our drawings will not display properly when opened by someone else because of missing or forgotten file dependencies. Consider how important this mistake could be if, for example, your architectural plans fail to show fire-rated wall linetypes when the drawings are opened outside the realm of your own computer system. It is with this concern in mind, that I set forth to create a series of custom complex linetypes closely emulating symbology expressed in the National CAD Standards, specifically for fire-rated wall linetypes (see below). The linetype graphics are specifically called out, using black diamonds; one diamond for 1 hour, two diamonds for two hour, etc.

The solution chosen was to use Windows TrueType fonts, selecting fonts that are universal to all modern Windows operating systems, thereby assuring the linetypes will display properly when opened on other computers. Wingdings and Webdings are good fonts to experiment with as they contain shapes potentially useful in complex linetypes, such as the solid diamond shape.

Caution: There may be, and probably are, many more Windows TrueType fonts on your computer, other than those standard fonts universal to all modern Windows systems. If a non-standard font is selected, you will have introduced a similar problematic condition whereby linetypes might display differently or wrong on other people's computers.

It is best practice to use only standard fonts.

In an article by Jim Rogers of CADreps on linetype customization, we get a solid tutorial on how to go about defining custom linetypes, so we’re not covering every aspect of custom complex linetypes here. Instead, we'll build upon that earlier Cadtales lesson. Let's review the standard AutoCAD "Hot_Water_Supply" linetype to get a better understanding of the techniques required to implement our custom fire-rated wall linetypes.

*HOT_WATER_SUPPLY,Hot water supply ---- HW ---- HW ---- HW ----
A,.5,-.2,["HW",STANDARD,S=.1,R=0.0,X=-0.1,Y=-.05],-.2

For complex linetypes, the important stuff is between the brackets, starting out with the text we want to place into our linetype, which in this example is the uppercase "HW". This is followed by the name of a pre-existing textstyle, which is this case is: STANDARD. Since all AutoCAD drawings by default have a textstyle named STANDARD, AutoCAD can typically depend on it being there and available. The text size, rotation, and XY offset values follow.

In our case we want to use a textstyle other then STANDARD, specifically, a new textstyle named SYMB defined to use the Wingdings font. However, it's important to note that if I attempt to load my custom linetype into a new drawing, the load will fail because the textstyle named SYMB does not pre-exist in the drawing. So, we'll need a mechanism to ensure that the custom textstyle does exist prior to attempting to load the linetypes. We'll get to that later. First, let's examine a new 1 Hour Fire-Rated Wall linetype.

*1HR-FireRatedWall,1 hr fire-rated wall line ----t----t----t----
A,.20,-.09,["t",SYMB,S=.062,R=0.0,X=-0.072,Y=-.0285],-.0038

It starts out, as all linetype definitions do, with an asterisk followed by the name of the linetype. Nest is a text description of linetype’s purpose, and an optional visual representation of the linetype. The second line begins with the letter A (as it must), followed by a line segment of .20 AutoCAD units, then a space or gap of .09 units. Next, we get to the text portion within the brackets. It starts out entering a lower case "t," which, when the font is set to Wingdings, corresponds to the diamond character. Check it out, make a textstyle using Wingdings, then use the TEXT or MTEXT command and enter "t" and, like magic, a diamond appears. It is followed by text size, rotation, and XY offset values. Notice the use of three and four decimal places for precise placement of the diamond. (It was necessary to zoom in very close on the test linetype to fuss with the symbol positioning to center it with the line. (Wingding symbols will often come in off center, so it maybe necessary to tweak the XY offset values.)

Let's repeat the process for a 2 hour fire-rated wall linetype.

*2HR-FireRatedWall,2 hr fire-rated wall line ----tt----tt----tt----
A,.20,-.09,["t",SYMB,S=.062,R=0.0,X=-0.072,Y=-.0285],-.0038,["t",SYMB,S=.062,R=0.0,X=-.036,Y=-.0285],-.044

The first pattern is repeated, then appended with a second text portion to add the second diamond. Notice in the second text portion, the X offset is halved so that two diamonds actually touch. Also, the final gap amount is changed to accommodate the wider text portion.

For the 3 hour fire-rated wall linetype, it's just a copy of the 2-hour linetype, with yet one more text portion added to get the third diamond - and the offsets and gaps tweaked accordingly. Because we're dealing with offsets in the thousandth of a unit in some case, it may take some effort and numerous reloads of the linetype to get it right. [Reloads may be faster if your linetype development is done in a separate drawing, then use Design Center to redefine the linetype.]

*3HR-FireRatedWall,3 hr fire-rated wall line ----ttt----ttt----ttt----
A,.20,-.09,["t",SYMB,S=.062,R=0.0,X=-0.072,Y=-.0285],-.0038,["t",SYMB,S=.062,R=0.0,X=-.036,Y=-.0285],.0038,
["t",SYMB,S=.062,R=0.0,X=-.001,Y=-.0285],-.079

The National CAD Standards include affiliated linetype standards for fire-rated smoke barrier lines, the graphic representation is the same as the fire-rated wall linetypes with an uppercase "S" placed next to the diamond. Here is an example:

*1HR-SmokeBarrier,1 hr fire-rated smoke barrier line ----tS---tS---tS---
A,.20,-.09,["t",SYMB,S=.062,R=0.0,X=-0.072,Y=-.0285],-.0038,["S",STANDARD,S=.06,R=0.0,X=-0.015,Y=-.0285],-.047

In the example above, the first half of the linetype definition is the same as the 1 hour fire-rated wall linetype. In the second portion we introduce the "S" text using textstyle STANDARD, and the appropriate XY offsets, followed by a final gap amount that ensures the gap on the left of the symbol is equal to the gap on the right side. In our implementation of AutoCAD, we ensure that textstyle STANDARD is defined with ROMANS.SHX instead of TXT, to get smoother, better looking uppercase letter "S" in this linetype, rather than the segmented "S" produced with the TXT.SHX font.

Implementation