|----------|----------------------------------------------------|
| 16       | if set, table entry is externally dependent on     |
|          | an xref                                            |
|----------|----------------------------------------------------|
| 32       | if this bit and bit 16 are both set, the           |
|          | externally dependent xref has been successfully    |
|          | resolved                                           |
|----------|----------------------------------------------------|
| 64       | if set, the table entry was referenced by at least |
|          | one entity in the drawing the last time the drawing|
|          | was edited. (this flag is for the benefit of       |
|          | autocad commands; it can be ignored by most        |
|          | programs that read dxf files, and need not be set  |
|          | by programs that write dxf files)                  |
+---------------------------------------------------------------+</pre>
    <pre>the following are the groups used for each type of table item. all 
groups are present for each table item.</pre>
    <pre>appid     2 (user-supplied application name), 70 (standard flag
          values).
          these table entries maintain a set of names for all 
          applications registered with a drawing.</pre>
    <pre>dimstyle  2 (dimension style name), 70 (standard flag values), and 
          the following, described by dimension variable name: 
          3 (dimpost), 4 (dimapost), 5 (dimblk), 6 (dimblk1), 
          7 (dimblk2), 40 (dimscale), 41 (dimasz), 42 (dimexo), 
          43 (dimdli), 44 (dimexe), 45 (dimrnd), 46 (dimdle), 
          47 (dimtp), 48 (dimtm), 140 (dimtxt), 141 (dimcen), 
          142 (dimtsz), 143 (dimaltf), 144 (dimlfac), 145 (dimtvp), 
          146 (dimtfac), 147 (dimgap), 71 (dimtol), 72 (dimlim), 
          73 (dimtih), 74 (dimtoh), 75 (dimse1), 76 (dimse2), 
          77 (dimtad), 78 (dimzin), 170 (dimalt), 171 (dimaltd), 
          172 (dimtofl), 173 (dimsah), 174 (dimtix), 175 (dimsoxd), 
          176 (dimclrd), 177 (dimclre), 178 (dimclrt).</pre>
    <pre>ltype     2 (linetype name), 70 (standard flag values), 3 
          (descriptive text for linetype), 72 (alignment code; value 
          is always 65, the ascii code for `a'), 73 (number of dash 
          length items), 40 (total pattern length), and optionally: 
          49 (dash length 1), 49 (dash length 2), and so on.</pre>
    <pre>layer     2 (layer name), 70 (standard flag values), 62 (color 
          number, negative if layer is off), 6 (linetype name).
          in addition to the standard flags, the 70 group flag is 
          bit coded as follows:</pre>
    <pre>          table 11-6. group 70 bit codes for layer table
          +=====================================================+
          | flag bit | meaning                                  |
          | value    |                                          |
          |----------|------------------------------------------|
          | 1        | if set, layer is frozen                  |
          |----------|------------------------------------------|
          | 2        | if set, layer is frozen by default in    |
          |          | new viewports                            |
          |----------|------------------------------------------|
          | 4        | if set, layer is locked                  |
          +-----------------------------------------------------+
 </pre>
    <pre>          if no value (0) is set, the layer is on and thawed. the  
          fourth bit (8) and the eighth bit (128) are not used.
          xref-dependent layers are output during dxfout. for these  
          layers, the associated linetype name in the dxf file is  
          always continuous.</pre>
    <pre>style     2 (style name), 70 (standard flag values), 40 (fixed text  
          height; 0 if not fixed), 41 (width factor), 50 (oblique  
          angle), 71 (text generation flags), 42 (last height used),  
          3 (primary font filename), 4 (big-font file name; blank  
          if none).</pre>
    <pre>          if the third bit (4) is set in the 70 group flags, this  
          is a vertically oriented text style.</pre>
    <pre>          a style table item is used to record shape file load  
          requests also. in this case the first bit (1) is set in  
          the 70 group flags and only the 3 group (shape filename)  
          is meaningful (all the other groups are output, however).
 </pre>
    <pre>          the text generation flags are a bit-coded field with the  
          following bit meanings:</pre>
    <pre>          table 11-7. group 71 bit codes for style table
          +=====================================================+
          | flag bit | meaning                                  |
          | value    |                                          |
          |----------|------------------------------------------|
          | 2        | text is backward (mirrored in x)         |
          |----------|------------------------------------------|
          | 4        | text is upside down (mirrored in y)      |
          +-----------------------------------------------------+</pre>
    <pre>ucs       2 (ucs name), 70 (standard flag values), 10, 20, 30
          (origin), 11, 21, 31 (x axis direction), 12, 22, 32 
          (y axis direction). all in world coordinates.</pre>
    <pre>view      2 (name of view), 70 (standard flag values), 40 and 
          41 (view height and width, in dcs), 10 and 20 (view 
          center point, in dcs), 11, 21, 31 (view direction from 
          target, in wcs), 12, 22, 32 (target point, in wcs), 
          42 (lens length), 43 and 44 (front and back clipping 
          planes - offsets from target point), 50 (twist angle), 
          71 view mode (see viewmode system variable in appendix a).</pre>
    <pre>          if the first bit (1) is set in the 70 group flags, this 
          is a paper space view.</pre>
    <pre>          (see chapter 2 of the &quot;autolisp programmer's reference&quot; 
          for information on dcs, the display coordinate system.)</pre>
    <pre>vport     2 (viewport name), 70 (standard flag values), 10 and 20 
          (lower-left corner of viewport; 0.0 to 1.0), 11 and 
          21 (upper-right corner), 12 and 22 (view center point, 
          in wcs), 13 and 23 (snap base point), 14 and 24 (snap 
          spacing, x and y), 15 and 25 (grid spacing, x and y), 16, 
          26, 36 (view direction from target point), 17, 27, 37 
          (view target point), 40 (view height), 41 (viewport aspect 
          ratio), 42 (lens length), 43 and 44 (front and back 
          clipping planes; offsets from target point),50 (snap 
          rotation angle), 51 (view twist angle), 68 (status field), 
          69 (id), 71 (view mode; see viewmode system variable in 
          appendix a), 72 (circle zoom percent), 73 (fast zoom 
          setting), 74 (ucsicon setting), 75 (snap on/off), 76 (grid 
          on/off), 77 (snap style), 78 (snap isopair).</pre>
    <pre>          the vport table is unique in that it may contain several 
          entries with the same name (indicating a multiple-viewport 
          configuration). the entries corresponding to the active 
          viewport configuration all have the name *active. the 
          first such entry describes the current viewport.
</pre>
    <pre>blocks section
--------------
the blocks section of the dxf file contains all the block 
definitions. this section contains the entities that make up the 
blocks used in the drawing, including anonymous blocks generated by 
the hatch command and by associative dimensioning. the format of the 
entities in this section is identical to those in the entities 
section described later, so see that section for details. all 
entities in the blocks section appear between block and endblk 
entities. block and endblk entities appear only in the blocks 
section. block definitions are never nested (that is, no block or 
endblk entity ever appears within another block-endblk pair), 
although a block definition can contain an insert entity.</pre>
    <pre>external references are written in the dxf file as any block 
definition, except they also include a text string (group code 1) of 
the path and filename of the external reference. this is the text 
string format:</pre>
    <pre>   xref filename
</pre>
    <pre>entities section
----------------
entity items appear in both the block and entities sections of the 
dxf file. the appearance of entities in the two sections is 
identical.</pre>
    <pre>the following gives the format of each entity as it appears in the 
file. some groups that define an entity always appear, and some are 
optional and appear only if they differ from their default values. 
in the following discussion, groups that always occur are given by 
their group number and function, while optional groups are indicated 
by -optional n following the group description. n is the default 
value if the group is omitted.</pre>
    <pre>programs that read dxf files should not assume that the groups 
describing an entity occur in the order given here. the end of the 
groups that make up an entity is indicated by the next 0 group, 
beginning the next entity or indicating the end of the section.</pre>
    <pre>remember that a dxf file is a complete representation of the drawing 
database, and that as autocad is further enhanced, new groups will 
be added to entities to accommodate additional features. 
accommodating dxf files from future releases of autocad will be 
easier if you write your dxf processing program in a table-driven 
way, ignoring any groups not presently defined, and making no 
assumptions about the order of groups in an entity.</pre>
    <pre>each entity begins with a 0 group identifying the entity type. the 
names used for the entities are given on the following pages. every 
entity contains an 8 group that gives the name of the layer on which 
the entity resides. each entity may have elevation, thickness, 
linetype, or color information associated with it.</pre>
    <pre>if handles are enabled, every entity has a 5 group containing its 
handle (as a string representing a hexadecimal number).</pre>
    <pre>the following groups are included only if the entity has nondefault 
values for these properties. when a group is omitted, its default 
value upon input (when using dxfin) is indicated in the third 
column. if the value of a group is equal to the default, it is 
omitted upon output (when using dxfout).</pre>
    <pre>table 11-8. group codes common to all entities
+==================================================================+
| group  | meaning                                 | if omitted,   |
| code   |                                         | defaults to...|
|--------|-----------------------------------------|---------------|
| 6      | linetype name (if not bylayer). the     | bylayer       |
|        | special name byblock indicates a        |               |
|        | floating linetype                       |               |
|--------|-----------------------------------------|---------------|
| 38     | elevation (if nonzero). exists only in  | 0             |
|        | output from versions prior to r11.      |               |
|        | otherwise, z coordinates are supplied   |               |
|        | as 3x-groups as part of each of the     |               |
|        | entity's defining points                |               |
|--------|-----------------------------------------|---------------|
| 39     | thickness (if nonzero)                  | 0             |
|--------|-----------------------------------------|---------------|
| 62     | color number (if not bylayer). zero     | bylayer       |
|        | indicates the byblock (floating) color. |               |
|        | 256 indicates the bylayer color         |               |
|--------|-----------------------------------------|---------------|
| 67     | absent or zero indicates entity is in   | 0             |
|        | model space. one indicates entity is    |               |
|        | in paper space, other values are        |               |
|        | reserved                                |               |
|--------|-----------------------------------------|---------------|
| 210,   | these groups are included for each line,| 0,0,1         |
| 220,   | point, circle, shape, text, arc, trace, |               |
| 230    | solid, block reference, polyline,       |               |
|        | dimension, attribute, and attribute     |               |
|        | definition entity if its extrusion      |               |
|        | direction is not parallel to the world  |               |
|        | z axis. they indicate the x, y, and z   |               |
|        | components of the entity's extrusion    |               |
|        | direction                               |               |
+------------------------------------------------------------------+</pre>
    <pre>the rest of the groups that make up an entity item are described 
next. many of the entities include &quot;flag&quot; groups. these are integer 
codes (6x or 7x groups) that encode various pieces of information 
regarding the entity, and are specific to the particular entity 
type. in the following descriptions, the term bit-coded means that 
the flag contains various true/false values coded as the sum of the 
bit values given. any bits not defined in the following section 
should be ignored in t