Troubleshooting AutoCAD DXF and DWG File Conversions

							Troubleshooting AutoCAD DXF and DWG File Conversions
… by Noel H. Browning

I would not even attempt to convert a General CADD Pro drawing file to AutoCAD unless it was first drawn in
a manner that would overcome most of the drawing file format differences. This approach requires that many
excellent features available in the Generic CADD based programs can not be used, resulting in output plots
that, I believe, are far less professional in appearance. The outstanding user interface in these programs more
than make up for any conversion problems. In other words, producing a Virtual 2D AutoCAD drawing is just
much faster and easier to do. When you save as DWG or DXF you will find that the AutoCAD file resulting is
                                                       s
far more primitive than Generic’s or General CADD' because AutoCAD was originally designed to work well
within the limitations of pen plotters and not to embody Good Drafting Practice.

AutoCAD has more than 11 file Versions, AutoCAD LT has 6.
Autodesk has released many different versions of AutoCAD over the years. Drawing DWG file formats include:
R-2.5, R-2.6, R-9, R-10, R-11/12, R-13, R14, R-2000, R-2002, and the current R-2004. There are about 6 different
file formats for AutoCAD LT. Releases for Windows have different color palettes than the older DOS versions.
Until recent versions there was an updated DXF file format for each release. Files are upwardly compatible but
generally files cannot be saved as earlier formats. For example, this means that you can load a converted R-11/12
DWG or DXF file from Generic CADD 6.1.5 into AutoCAD R-2004 but you can’t load an R-2004 file into Generic.
Tip: The use of the larger DXF text format should result in a much cleaner file conversion.
The 3.1 version of General CADD Pro supports the R-9 through R-14, 2002, & 2004 .DWG file formats,
plus Generic friendly versions of the AutoCAD files.

AutoCAD Text has fewer properties.
Font character height & width with justification left, center, right, or vertical are supported, however letter spacing
percentage is a part of the SHX design as are filled and mono-spaced fonts and can only be changed by substituting
a different font. Text lines may also be scaled to fit into a designated drawing area as a sort of word wrap. Determine
correct aspect and percentage settings by trial and error. Tip: RomanS will retain the string length pretty well if text
spacing is set to 36% and the aspect ratio to 0.8 and when using the mono-text setting try the 0.8 aspect. The string
origin points may have moved in your new DWG file especially with center or right justified text. Be sure to check
your text string locations and MOVE and/or ROTATE them back to the correct position especially any lettering
placed at odd angles. Text paragraphs convert to AutoCAD as individual lines. Fonts that are not included in the
target AutoCAD program convert to the mono-text default TXT.SHX font. This will be an ongoing problem until a
font to SHX utility is developed for GCP.
Tip: Only fonts converted from SHX files seem to work well for body text, dimension text, and leader text.
AutoCAD versions have different Color numbers.
The 256 colors available have been reassigned for the AutoCAD for Windows programs so if you save a
Generic 6.1.5 and have the same color box checked you will get the AutoCAD DOS program color numbers
most of which will now be different colors in Windows. Tip: To support DWG pen plotting limit GCP color
selections to only the original CGA colors 7 through 15. Several of the same AutoCAD Windows colors have
been assigned two different color numbers. Refer to the Table appended below. Note: AutoCAD 2004 supports
all 16,777,216 Windows colors.
The GCP palette supports more colors and does not provide exactly the same 256 colors as AutoCAD.
Observed that some colors changed slightly when exporting DWG files.
General CADD colors seem to convert to the 256 DWG colors very well.
    The Generic CADD color palette differ so much from AutoCAD’s that color conversion may be a problem
with many of the very low and the higher numbered colors.
AutoCAD Hatches have their limitations.
CADD converts hatches to blocks while converting to DWG and this seems to be a simple workable solution,
however only certain simple, straight line, closed objects may be hatched with a single hatch in AutoCAD. The
latest versions of AutoCAD have added several new hatching options.
Tip: Hatches may be exploded to avoid these problems.
   CADD hatches convert to AutoCAD as blocks.
AutoCAD Fills are very simple hatch-like Critters.
They are just fine hatches drawn with the HATCH, SOLID command. Some refer to them as plotter pen scribbles.
Only certain simple closed objects may be filled in older versions. This explains the Donut entity seen only in a
DWG file. In AutoCAD there is no filling concentric circles or triangle shapes. An object with arcs or curves will
fill with several Trace objects. General CADD supports true flood fills that print well but convert to DWG as a
collection of 4-point trace/fills with no curved outlines. Filled SHX fonts actually have a fine exploded cross hatch.
For some unexplained reason, DWG fills do import into CADD. Tip: The only sure way to mimic a flood fill is to
use a very fine crosshatch in CADD and then explode it.
   General CADD flood fills export to AutoCAD as native DWG 4-point flat sided Traces.
AutoCAD Layers have different properties and their quantity is unlimited.
Generic is limited 256 layers, General CADD is limited to a maximum of 1,024 layers, enough for most any
drawing or layer system. Entity properties may be assigned to a layer in AutoCAD. AutoCAD layer 0 is pre-
assigned white as it’s default color along with the solid line type-0. Layer-0 has other special qualities relating
to Drawing Blocks.
AutoCAD layers have a database place number but to exist any DWG layer except zero must be named. Layers
are listed on screen in alphabetical order. Merged drawings and imports into other programs can create many
nasty layer problems. CADD layers each also has a database place and an assigned number that may be named.
The first layer used or named in a CADD takes place-1 in both databases. Revising a layer name or the data on
it may change its place in either programs file database. This sort of thing can result in the CADD layer-0 being
at another layer database place number and may result in a very confused drawing file if passed back and forth
between the two programs. Tip: Start a new Virtual DWG in CADD by placing a short Color-15, Solid line on
Layer-0 using it for no other data. A Wish List item for a new CADD feature that will help solve these problems
is the proposed command YO laYer reOrder by number that will place layers with larger numbers after (on top
of) the layers with smaller numbers. Bjorn has written a macro for GCP that performes this function.
Tip: If your CADD drawing has a small number of layers use the YG command to step through each layer
starting with layer-0, then layer-1, etc. You don’t need to actually change any of the properties for this to work
as long as you use [Enter] after each YG.

AutoCAD Line Types are standard or custom but only have world scale.
Line type scale is supported in GCP but the program also includes 20 device scaled line types as well as 60
world scaled line types. A line type name used in GCP will convert to the same name in a DWG file. Be sure to
reset the line type scale in AutoCAD. For any additional line types not present in the target program, a new
AutoCAD custom line type is created by GCP during conversion.
General CADD line types convert to DWG line types very well.

AutoCAD does not fully support Curves.
The particular kind of curve created by AutoCAD {using the Spline command} is a Non-Uniform Rational B-
spline (NURBS).
Tip: Limit the use of Bezier or other Complex curves in your General CADD drawing. AutoCAD simply
    t
can'reproduce them.
   Complex Curves and true Ellipses convert to DWG as B-spline curves.
AutoCAD has Polyline & Trace entity objects.
Many AutoCAD users used polylines to replace their sadly missing line width property. Polylines are closed
objects made up of filled joined lines and arcs intended originally for printed circuit board design. The joined
Line + Arc object was not supported in Generic CADD and is not supported in GCP. Plines may have line
width and may be edited to become a fitted spline curve. Filled joined Arc, Curve, and Line objects can be
created as Components in GCP and work much better than AutoCAD Polylines.
AutoCAD Traces are similar to filled double lines.
   Polylines convert to CADD as lines, arcs or CV splines and the fills are changed to groups of 4-flat sided fills
with no Arcs.

In AutoCAD the Line Weight entity property was the most important missing feature.
The Line Weight property was finely added to AutoCAD R-2000. Most archived DWG files do not have line width.
Until 1999 all AutoCAD users assigned pen numbers to their line colors or layers. Modern ink-jet printer/plotters
can assigned line width to individual line colors or width can be assigned to color with the AutoCAD print utility.

AutoCAD Blocks are not Components.
They are DWG files saved in the current drawing or saved to disk for future use. They may be merged (as imbedded
files) into another DWG file and like components they have their own scale factor. Components are truer object
entities and work far better. Compound components with differing rotations have always been a conversion problem
so avoid them. Tip: Make all your components on their own neutral layer so that turning off layers in AutoCAD will
not turn the same layers off inside the blocks. Note that Blocks created on DWG layer-0 will change from a solid
line and white color to the By-Layer properties of the current layer. GCP does not have the confounded entity
property by layer feature because most GCP users do not want it. Text in Blocks are a 2-way conversion problem.
Tip: Use only the continuous linetype-0 and explode all included text to their line entities before creating your
components and the text will be placed correctly when exported to AutoCAD.
CADD components convert to Blocks moderately well.
AutoCAD Dimensions are different.
  Problems with Font and Unit conversion may require extensive revisions to the AutoCAD drawing.

AutoCAD Point entities may have 20 different shapes.
CADD is limited to the single cross + shape. A good practice is to use components rather than points with the
added benefit of attaching attributes to record elevations and other information for your points.

AutoCAD Units have no base unit.
The database unit for CADD is the ISO inch that is defined as being exactly 25.4 mm long. The AutoCAD
database unit remains undefined in the drawing file and is set in the program by the user.
This AutoCAD unit-less feature may cause some CADD files to seem to convert to DWG files out of scale. The
same problem may occur when importing DWG’s into CADD.
Important Tip: When importing or exporting AutoCAD files be sure to select the unit required with the LO,
Units setting command.

AutoCAD allows the user to Group objects.
The Object Group is also a feature in the Generic CADD 3D programs. Object Groups are assigned names.
The object group is not the same as the useful Layer Group feature found in MicroStation programs.
General CADD Pro does not support either Object or Layer Groups.

AutoCAD allows Vector files to be Cross-Referenced.
This OLE-like feature was not supported in Generic & but is now supported in General CADD Pro 4.0 and is
only a problem when importing files. Without the separate referenced DWG files even opening the complete
drawing in AutoCAD may be a problem. Tip: This problem can be worked around by obtaining the DWG file
that was used as an X-Ref, converting it, and then inserting it into your CADD drawing.
Generic CADD does not support the cross referencing of drawing files.
General CADD Pro 4.0 adds Tabbed Drawings as a way of supporting cross-referenced drawings.
Type NT on the keyboard or click the New Tab option in then V4 Commands DropDown Menu. AutoCAD
drawings that contain XREFS will load with the XREFS in individual TABS.
AutoCAD files can link or embed Raster files.
General CADD supports JPG and other Raster files very well.

AutoCAD files may contains 3D elements.
Autodesk unwisely added 3D wireframe modeling features to their 2D AutoCAD program creating a messy
goulash of the plane and solid geometry elements. Generic released their 3D software as separate program
modules from which Views and Sections could be saved as Generic 2D files. General CADD like the Generic
2D programs does not directly support 3D models. General Software plans to provide 3D modeling software in
the future. Tip: Use programs like Rhino, SketchUp, or ChiefArchitect to do 3D modeling and save Views,
Sections, etc and then DXF them to your CADD program for the development of the final 2D working
drawings.

AutoCAD supports Paper Space.
GC and GCP only work in 2D Space and not in Paper Space.
  This import problem can only be solved by first editing the DWG file in an AutoCAD based CAD program.
The file cannot be returned to AutoCAD with paperspace ports.

AutoCAD has added many Short-Cut Commands.
These are alias commands and may be revised by the user. These new one and two letter commands help speed
up the use of the program but still require many additional [Ctrl] and [Enter] key strokes or right mouse button
clicks and can’t compare to the much faster and more logical Generic CADD style command line user interface.
Saving a CADD file as an AutoCAD file is about as easy as translating Modern English into
Ancient Greek. Tip: Use an AutoCAD Clone program to review and correct your converted CADD drawing if
you must send it off to an AutoCAD user. Two reasonable cost Clones that I know of are Vdraft and IntelliCAD.

CADD Color Table— DOS 16 Color CGA versus Windows 256 Color VGA Pallets
 DOS QBasic CGA        Windows       Auto-    Auto-        Windows 95 Kodak          Video Display Colors    Printer Dithered Colors
 Colors also used in   RGB           CAD      CAD          VGA Color System          Phosphors 0 to 255      Ink 0 to 100%
 Generic CADD          Equivalent    DOS      Windows      Hue    Sat     Lum        R      G        B       C        M       Y      K
 0-Black               0             0        0            None      0       0       0       0       0       19      19     19      80
 1-Dark Blue           8388608       13       178          160       240     60      0       0       128     70      70     19      29
 2-Dark Green          32768         11       98           80        240     60      0       128     0       70      19     70      29
 3-Dark Cyan           8421376       12       138          120       240     60      0       128     128     70      19     19      29
 4-Dark Red            128           9        18           0         240     60      128     0       0       19      70     70      29
 5-Dark Magenta        8388736       14       218          200       240     60      128     0       128     19      70     19      29
 6-Dark Yellow         32896         10       58           40        240     60      128     128     0       19      19     70      29
 7-Light Gray          12632256      15       9 & 254      None      0       181     192     192     192     20      20     20      4
 8-Medium Gray         8421504       8        8 & 251      None      0       120     128     128     128     19      19     19      29
 9-Light Blue          16711680      5        5 & 170      160       240     120     0       0       255     100     100    0       0
 10-Light Green        65280         3        3 & 90       80        240     120     0       255     0       100     0      100     0
 11-Light Cyan         16776960      4        4 & 130      120       240     120     0       255     255     100     0      0       0
 12-Light Red          255           1        1 & 10       0         240     120     255     0       0       0       100    100     0
 13-Light Magenta      16711935      6        6 & 210      200       240     120     255     0       255     0       100    0       0
 14-Light Yellow       65535         2        2 & 50       40        240     120     255     255     0       0       0      100     0
 15-White             16777215     7         7 & 255       None    0     240      255    255       255     0         0      0       0
Note: The 6-dark Generic CADD colors have been revised in General CADD Pro to provide much better on screen visibility.

                                                                                           File: LivingWith_v3.doc Draft: 7/25/04
                                                                                                                  Noel@cirs.com
                                                                                                            www.caddvillage.com