Some of the best clients of my CADD service require that we provide them with AutoCAD .DWG files after we complete projects for them. This has consumed many hours of computer time and required a lot of head scratching here at our little studio. What follows is a modest attempt to again share some of the techniques we have learned by trial and error.

True CADD programs all utilize the same trigonometric vector data for their basic line drawings but differ greatly in many other respects. Fills, Hatches, Attributes, Line Widths, Line Types, Line Colors, Layers, Symbol/Component/Blocks, and Text Faces are not quite the same creatures in one Computer Aided Design program as they are in another.

Fills may not transfer at all to other programs. AutoCAD does not have true fills but uses hatch lines drawn very close together. These plot as fills but and only polygons may be filled. This limitation may explain why there is a Donut entity. CADD 6.0 will import AutoCAD fills but AutoCAD will not (as yet) import CADD 6.0 Fills.

Hatches sometimes do strange things when exported to AutoCAD The best advice here is either to avoid them or explode them before transferring them.

Attributes of components will not be discussed here. Conversion problems may exist but we have not identified them as yet.

Line Widths are available in CADD 6.0 and VersaCad but are not one of the AutoCAD line properties. AutoCAD uses traces which are like the CADD 6.0 [L2] filled double line. AutoCAD also has the polyline (a strange beast) which allows filled complex line shapes. Many AutoCAD operators misuse the Polyline as a substitute for line widths. They avoid changing pens with 1-pen plotters but this practice can use up a lot of drawing file memory. Polylines have few practical uses and are not on my wish list for future versions of Generic CADD. Polylines convert into CADD 6.0 as ordinary lines and arcs.

Line Types are not standard from one software to another. CADD 6.x has 255 standard line types, ACad 12 has 25 types but allows others to be created. Warning!! AutoConvert does not support the new AutoCAD /2 and X2 line types.

AutoCAD seems to have no true curved lines. Very short line segments are used to mimic curves, circles, and arcs.

Components act as individual objects in CADD 6.0 but are just a special sort of drawing file in AutoCAD. Blocks are often created as white lines on Layer 0 in ACad so that later they can take on the properties preset into the layer they are inserted on. I draw all components on layers set aside specifically for components. This prevents them from being hidden accidentally in ACad where the layers inside a Block are hidden just like that same layer outside a Block. Another observed problem is that sometimes the rotation of parts within a compound component will be changed during the drawing file conversion. To prevent this avoid mirroring, negative component scales, or rotation inside compound components.

When text is used in a component as part of a reference symbol, the character will usually move out of place during the conversion. This is because the origin point of the individual letters differ in FNT and SHX fonts. We never use unexploded fonts in our components.

Layers differ also. They have at least three properties; data record number, layer number, and name. The two property numbers are usually the same in ACad. When unnamed Generic layers are converted to AutoCAD they are given the CADD 6.0 layer number as an AutoCAD layer name and are usually out of their original order. Then they show up named (L1, L2, etc.) in CADD 6.0 if they are re-imported. This happens because the data record number is assigned in CADD 6.0 when the layer is first used. This will not be apparent to the user. The layer number (as a sort of default name) is pre-assigned in CADD 6.0 with a maximum of 255 layers available. The maximum number of ACad layers is limited only by available memory. I have never imported a .DWG file into a .GCD file that exceeds the 255 layer limit but we know that there is a maximum number of AutoCAD blocks (256) that can be imported into a CADD 6.0 drawing file and you will probably also lose those extra layers above 255. Layer-0 in ACad has special properties and is always present in the DWG file. It is good practice to start your CADD 6.0 drawing in layer-0 and place a short line at 00,00. Use only Color-15, Type-0, and Width-0. Do this before any other drawing so that Layer-0 is near the start of the .GCD and .DXF files. The CADD 6.0 drawing should not have any other data on Layer-0. The order of the layers will be sorted by record number when they are converted. AutoCAD allows the operator to assign line type and line color to a named layer. At CADD Cottage we use "Go To Layer" batch files to set the line properties in our CADD 6.0 drawings.

Text font faces are more difficult to create in AutoCAD than CADD 6.0 and in the early years were drawn using a rather primitive form of vector file made up of only straight line segments. Each .SHX file must be either mono or proportional spaced. Text properties such as Outline and Filled are fixed in the AutoCAD shape file selected. Filled .SHX files actually have cross hatch lines with closer hatch lines used for larger height fonts. The Helvetica text face for ACad will typically come in at least three fonts: outline, high density fill, and low density fill. Both outline text and filled text of the same face can be in the same .DWG file. You can use a Generic outline font that has not been changed to a fillable font for conversion to an AutoCAD outline font. We have created two identical versions of several Generic type faces. For our Leroy style Generic face we converted the Leroy AutoCAD fonts to LER.FNT and MONOLER.FNT. These convert well to the AutoCAD LER.SHX and MONOLER.SHX. Using these two fonts we are able to write mono spaced schedules in CADD, so the columns line up, and write our drawing notes in the same face but proportionally spaced. Never use the same Generic font with both proportional and monotext lines if you plan to convert to .DXF. The almost insurmountable challenge with text conversion is string length. Use only converted .SHX fonts in Generic. Set the aspect ratio to 0.8 and the character spacing to 36% for the RomanS font and you will get text lines of about the same length. Other fonts may vary as the percent spacing has a fixed value designed into the AutoCAD font.

Drawing Exchange File Utilities and CADD Program versions are only upwardly compatible. This non-compatibility can lead to some real problems. You must check to know which version you are attempting to .DXF into. Example: An AutoCAD R-11 .DWG or .DXF file will not work in a R-10 or older program.

It can be very frustrating to the recipient of your .DXF file if a lot of time is wasted revising your drawing to make it work well in their program. Use only the standard AutoCAD fonts and the line types common to both programs. Take pride in your drawing ability and provide others with the best planned drawing exchange file you can produce.

File: GRUMBLE3.DOC 03/29/93