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<p align="center"><font size="5" color="#0000ff">drawing interchange and file formats 

release 12</font></p>

<div align="center"><center>



<table border="0" width="80%">

  <tr>

    <td width="100%"><pre>copyright (c) 1982-1990, 1992 autodesk, inc. all rights reserved</pre>

    <pre>autocad can be used by itself as a complete drawing editor. in some 

applications, however, other programs must examine drawings created 

by autocad or generate drawings to be viewed, modified, or plotted 

with autocad.</pre>

    <pre>for example, if you've made an architectural drawing with autocad, 

using inserted parts to represent windows, doors, and so on, you can 

process the drawing file and produce a bill of materials of all 

items used in the drawing, or even make energy-use calculations 

based on the area and the number and type of windows used. another 

possible application is to use autocad to describe structures and 

then send the descriptions to a more powerful computer for finite-

element structural analysis. you can compute stresses and 

displacements and send back information to display the deformed 

structure as an autocad drawing.</pre>

    <pre>since the autocad drawing database (.dwg file) is written in a 

compact format that changes significantly as new features are added 

to autocad, we do not document its format and do not recommend that 

you attempt to write programs to read it directly. to assist in 

interchanging drawings between autocad and other programs, a drawing 

interchange file format (dxf) has been defined. all implementations 

of autocad accept this format and are able to convert it to and from 

their internal drawing file representation.</pre>

    <pre>autocad also supports the initial graphics exchange specification 

(iges) file format. the information comprising an autocad drawing 

can be written out in iges format, and iges files can be read and 

converted to the autocad internal format.

</pre>

    <pre>ascii drawing interchange (dxf) files

*************************************</pre>

    <pre>this section describes the autocad dxf (drawing interchange file) 

format and the commands provided to read and write these files. dxf 

files are standard ascii text files. they can easily be translated 

to the formats of other cad systems or submitted to other programs 

for specialized analysis. autocad can also produce or read a binary 

form of the full dxf file. this feature is described in detail later 

in this chapter.

</pre>

    <pre>dxfout command - writing a dxf file

===================================

you can generate a drawing interchange file from an existing drawing 

by means of the dxfout command:</pre>

    <pre>   command: dxfout 	</pre>

    <pre>when autocad prompts you, respond with a filename or press 5 to 

accept the default.</pre>

    <pre>the default name for the output file is the same as that of the 

current drawing, but with a file type of .dxf. if you specify an 

explicit filename, you do not need to include a file type; .dxf is 

assumed. if a file with the same name already exists, the existing 

file is deleted. if you specify the file using a file dialogue box, 

and a file with the same name already exists, autocad tells you; 

allowing you to ok or cancel the deletion. next, dxfout asks what 

precision you want for floating-point numbers and permits output of 

a partial dxf file containing only selected objects.</pre>

    <pre>   enter decimal places of accuracy (0 to 16)/entities/binary &lt;6&gt;:</pre>

    <pre>the binary option is described later in this chapter.</pre>

    <pre>if you respond with &quot;entities&quot; (or just &quot;e&quot;), dxfout asks you to 

select the objects you want written to the dxf file. only the 

objects you select are included in the output file - symbol tables 

(including block definitions) will not be included. once you've 

selected the desired objects, autocad again prompts you for the 

numeric precision:</pre>

    <pre>   enter decimal places of accuracy (0 to 16)/binary &lt;6&gt;:

</pre>

    <pre>dxfin command - loading a dxf file

==================================

a drawing interchange file can be converted into an autocad drawing 

by means of the dxfin command:</pre>

    <pre>   command: dxfin  </pre>

    <pre>when autocad prompts you, respond with the name of the drawing 

interchange file to be loaded.

</pre>

    <pre>full dxfin 

----------

to load a complete dxf file, you must use dxfin in an empty drawing, 

before any entities have been drawn and before any additional block 

definitions, layers, linetypes, text styles, dimension styles, named 

views, named coordinate systems, or named viewport configurations 

have been created.</pre>

    <pre>note: if the drawing you are using as a prototype is not empty, you 

might find it helpful to open a new drawing using the no 

prototype... button of the create new drawing dialogue box, as 

described in chapter 4 of the &quot;autocad reference manual.&quot; you should 

also be aware that some third-party applications include an acad.lsp 

or .mnl file that modifies your drawing upon startup.</pre>

    <pre>if any errors are detected during the input, the new drawing is 

discarded. otherwise, an automatic zoom all is performed to set the 

drawing extents.

</pre>

    <pre>partial dxfin

-------------

if the current drawing is not empty, dxfin loads only the entities 

section of the dxf file, adding the entities found there to the 

current drawing. in this case, dxfin displays the message:</pre>

    <pre>   not a new drawing -- only entities section will be input.</pre>

    <pre>if errors are detected during such partial dxf input, the drawing is 

returned to the state it was in before the dxfin command. otherwise, 

the newly added entities are drawn.

</pre>

    <pre>auditing dxf files

------------------

to ensure that corrupt data is not imported into your drawing, you 

can instruct autocad to perform an audit after importing dxf files 

into your drawing with dxfin. when you use dxfin, the default action 

is to perform no automatic auditing. to activate automatic auditing, 

use the config command: </pre>

    <pre>   command: config</pre>

    <pre>your current autocad configuration appears. press 5 to continue. 

from the configuration menu select this option: </pre>

    <pre>   7. configure operating parameters</pre>

    <pre>from the operating parameter menu select this option: </pre>

    <pre>   9. automatic audit after igesin, dxfin, or dxbin</pre>

    <pre>answer y to this question: </pre>

    <pre>   do you want an automatic audit after igesin, dxfin, or dxbin?

   &lt;n&gt;: y</pre>

    <pre>return to the graphics screen by pressing 5 three times.</pre>

    <pre>note: this kind of audit only displays the errors autocad finds; it 

does not correct them. to correct problems, use the audit command on 

the drawing while you are in autocad, or manually edit the dxf file.

</pre>

    <pre>dxf file format

===============

this section describes the format of a dxf file in detail. it 

contains technical information that you need only if you write your 

own programs to process dxf files or work with entity information 

obtained by certain autolisp and ads functions.</pre>

    <pre>it would probably be helpful to produce a dxf file from a small 

drawing, print it out, and refer to it occasionally while reading 

the information presented next.

</pre>

    <pre>general file structure

----------------------

a drawing interchange file is simply an ascii text file with a file 

type of .dxf and specially formatted text. the overall organization 

of a dxf file is as follows:</pre>

    <pre>1. header section - general information about the drawing is found 

   in this section of the dxf file. each parameter has a variable 

   name and an associated value (see table 11-3 for a list of the 

   header variables).</pre>

    <pre>2. tables section - this section contains definitions of named 

   items.</pre>

    <pre>   o linetype table (ltype)

   o layer table (layer)

   o text style table (style)

   o view table (view)

   o user coordinate system table (ucs)

   o viewport configuration table (vport)

   o dimension style table (dimstyle)

   o application identification table (appid)</pre>

    <pre>3. blocks section - this section contains block definition entities 

   describing the entities that make up each block in the drawing.</pre>

    <pre>4. entities section - this section contains the drawing entities, 

   including any block references.</pre>

    <pre>5. end of file</pre>

    <pre>if you use dxfout's entities option, the resulting dxf file contains 

only the entities section and the end of file marker, and the 

entities section reflects only the objects you select for output.</pre>

    <pre>note: if you select an insert entity, the corresponding block 

definition is not included in the output file.</pre>

    <pre>a dxf file is composed of many groups, each of which occupies two 

lines in the dxf file. the first line of a group is a group code, 

which is a positive nonzero integer output in fortran i3 - that is, 

right-justified and blank filled in a three-character field (the 

exception to this is the four-digit extended entity data group 

codes, which are output in fortran i4). the second line of the group 

is the group value, in a format that depends on the type of group 

specified by the group code. although dxfout output has a fixed 

format, the dxfin format is free.</pre>

    <pre>the specific assignment of group codes depends on the item being 

described in the file. however, the type of the value this group 

supplies is derived from the group code in the following way:</pre>

    <pre>table 11-1. group code ranges

+================================+

| group code  | following value  |

| range       |                  |

|-------------|------------------|

| 0 - 9       | string           |

|-------------|------------------|

| 10 - 59     | floating-point   |

|-------------|------------------|

| 60 - 79     | integer          |

|-------------|------------------|

| 140 - 147   | floating-point   |

|-------------|------------------|

| 170 - 175   | integer          |

|-------------|------------------|

| 210 - 239   | floating-point   |

|-------------|------------------|

| 999         | comment (string) |

|-------------|------------------|

| 1010 - 1059 | floating-point   |

|-------------|------------------|

| 1060 - 1079 | integer          |

|-------------|------------------|

| 1000 - 1009 | string           |

+--------------------------------+</pre>

    <pre>thus a program can easily read the value following a group code 

without knowing the particular use of this group in an item in the 

file. the appearance of values in the dxf file is not affected by 

the setting of the units command: coordinates are always represented
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