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Re-using as-built cad drawings, or cad drawings supplied by manufacturers and external designers can be a real source of frustration. You want to re-use the graphical geometry so you don't have to redraw it. But the cad properties don't conform with what you are used to or need in your field of practice. This makes these drawings excruciatingly slow to work with, your production tools can't be used on them, and there will be a frequency of errors on the printout such that you are tempted to make quick fixes. That leaves us with problem drawings forever.

If you are considering changes to the coding that you use to define your objects, ultimately there need not be as many problem drawings created. But in the interim, what can you do to make it easier to work with the old drawings?

To upgrade a drawing, you need to translate the coding systems that have been used in the non-conforming drawing to the ones you need. There are two fundamental differences you have to deal with:

1. Two kinds of coding systems used. That is, one kind of coding uses cad properties to represent plotting characteristics only and the other kind represents the objects where colors, linetype names, and plotstyle names are variables that can have their own definitions in the form of lineweights, linetype patterns, and other plotting characteristics.

For example, a color is used explicitly to represent a lineweight rather than an object, and a linetype name is used explicitly to represent a dash-dot line pattern rather than part of an object.

The difficulty with lineweight and pattern codes is that there are not enough unique definitions, and the same definition has to be used for another object. You can not convert all of the lineweights or linetypes of a given definition, but you need them to be changed for certain objects. You can automate the conversion of colors and linetype names representing the object to represent lineweights and patterns. But to convert lineweight and pattern codes into an object code, you have to manually select which objects to apply the code to.

2. Varying extents in the classification of objects. That is, cad properties are coded more specifically to represent only one kind of object versus being coded more generically to represent many kinds. For example, you can automate the conversion of many more specific layer names to more generic ones. But to change one to many, you have to manually select which objects to apply the new name to since those objects have been given no method of recording more specific identification.

Acting on the answers to the following questions helps to reduce the muddle and determine a process that will work for you until more companies adopt compatible systems:

• What is essentially IMPORTANT, and what can be LEFT as it is?
• What kind of system should your company use?
• Are the new codes going to be more SPECIFIC or more GENERIC?

Remember that when you use object classification, you can use the classifications as the basis for all of your sub-systems. That is, there is a standard linetype name, color, plotstyle name, and layer name defined for each of the objects. This enables you to uniquely identify the object for automated conversion of any code while the definitions can be used repetitively. The extent of

classification can be applied in varying degrees for the sub-systems. The plotstyle names are the most specific and the others can be as specific or generic was you need.

Here are some point by point methods for overcoming the difficulties when you encounter non-conforming codes:

General Rules:

1. If you are mostly a creator of drawings for delivery TO others, the extent of classification that you employ should tend to be more SPECIFIC than what the other companies use. Conversely, If you work with drawings received FROM others, the extent of classification that you employ should tend to be more GENERIC than what the other companies use.
2. The definition of a cad property that is used as a code has to be unique. You cannot use that definition for anything else. For example if color 30 is used as a major object code for a framed wall, and color 150 is used to define a concrete wall, the colors have lineweights but you can not use those colors to represent lineweights. You CAN use color 31, 33, 35, and 37 as lineweight codes for framed walls.
3. When you convert name codes to a more generic system you should allow consideration for changing the name to a more specific classification of the major class in the new system, and then define a new resource (e.g. a new layer, linetype, or plotstyle) under that name. In the least, you should flag those codes so the receiver of the drawing can consider adopting a more specific code.

Part 2 discusses answers to the questions posed above, and offer some special solutions for changing symbol blocks, linetypes, colors, layers, plotstyles, textstyles, and dimstyles.

Originally published in S-MAN E-NEWS by Softco Engineering Systems. Re-published by permission.

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