drawing interchange and file formats release 12(AutoCAD DXF 12.0版文件格式说明)
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
as decimal (or possibly scientific notation if very large) numbers,
and angles are always represented in decimal degrees with zero
degrees to the east of origin. variables, table entries, and entities are described by a group that
introduces the item, giving its type and/or name, followed by
multiple groups that supply the values associated with the item. in
addition, special groups are used for file separators such as
markers for the beginning and end of sections, tables, and the file
itself. entities, table entries, and file separators are always introduced
with a 0 group code that is followed by a name describing the item. note: the maximum dxf file string length is 256 characters. if your
autocad drawing contains strings that exceed this number, those
strings are truncated during dxfout. if your dxf file contains
strings that exceed this number, dxfin will fail.
group codes
-----------
group codes are used both to indicate the type of the value of the
group, as explained earlier, and to indicate the general use of the
group. the specific function of the group code depends on the actual
variable, table item, or entity description. this section indicates
the general use of groups, noting as "(fixed)" any that always have
the same function. table 11-2. autocad entity group codes (by number)
+===============================================================+
| group code | value type |
|------------|--------------------------------------------------|
| 0 | identifies the start of an entity, table entry, |
| | or file separator. the type of entity is given |
| | by the text value that follows this group |
|------------|--------------------------------------------------|
| 1 | the primary text value for an entity |
|------------|--------------------------------------------------|
| 2 | a name: attribute tag, block name, and so on. |
| | also used to identify a dxf section or table name|
|------------|--------------------------------------------------|
| 3-4 | other textual or name values |
|------------|--------------------------------------------------|
| 5 | entity handle expressed as a hexadecimal string |
| | (fixed) |
|------------|--------------------------------------------------|
| 6 | line type name (fixed) |
|------------|--------------------------------------------------|
| 7 | text style name (fixed) |
|------------|--------------------------------------------------|
| 8 | layer name (fixed) |
|------------|--------------------------------------------------|
| 9 | variable name identifier (used only in header |
| | section of the dxf file) |
|------------|--------------------------------------------------|
| 10 | primary x coordinate (start point of a line or |
| | text entity, center of a circle, etc.) |
|------------|--------------------------------------------------|
| 11-18 | other x coordinates |
|------------|--------------------------------------------------|
| 20 | primary y coordinate. 2n values always |
| | correspond to 1n values and immediately follow |
| | them in the file |
|------------|--------------------------------------------------|
| 21-28 | other y coordinates |
|------------|--------------------------------------------------|
| 30 | primary z coordinate. 3n values always |
| | correspond to 1n and 2n values and immediately |
| | follow them in the file |
|------------|--------------------------------------------------|
| 31-37 | other z coordinates |
|------------|--------------------------------------------------|
| 38 | this entity's elevation if nonzero (fixed). |
| | exists only in output from versions prior to r11 |
|------------|--------------------------------------------------|
| 39 | this entity's thickness if nonzero (fixed) |
|------------|--------------------------------------------------|
| 40-48 | floating-point values (text height, scale |
| | factors, etc.) |
|------------|--------------------------------------------------|
| 49 | repeated value - multiple 49 groups may appear |
| | in one entity for variable length tables (such |
| | as the dash lengths in the ltype table). a 7x |
| | group always appears before the first 49 group |
| | to specify the table length |
|------------|--------------------------------------------------|
| 50-58 | angles |
|------------|--------------------------------------------------|
| 62 | color number (fixed) |
|------------|--------------------------------------------------|
| 66 | "entities follow" flag (fixed) |
|------------|--------------------------------------------------|
| 67 | identifies whether entity is in model space or |
| | paper space |
|------------|--------------------------------------------------|
| 68 | identifies whether viewport is on but fully off |
| | screen, is not active, or is off |
|------------|--------------------------------------------------|
| 69 | viewport identification number |
|------------|--------------------------------------------------|
| 70-78 | integer values such as repeat counts, flag |
| | bits, or modes |
|------------|--------------------------------------------------|
| 210, | x, y, and z components of extrusion direction |
| 220, | (fixed) |
| 230 | |
|------------|--------------------------------------------------|
| 999 | comments |
|------------|--------------------------------------------------|
| 1000 | an ascii string (up to 255 bytes long) in |
| | extended entity data |
|------------|--------------------------------------------------|
| 1001 | registered application name (ascii string up to |
| | 31 bytes long) for xdata (fixed) |
|------------|--------------------------------------------------|
| 1002 | extended entity data control string ("{" or "}") |
| | (fixed) |
|------------|--------------------------------------------------|
| 1003 | extended entity data layer name |
|------------|--------------------------------------------------|
| 1004 | chunk of bytes (up to 127 bytes long) in |
| | extended entity data |
|------------|--------------------------------------------------|
| 1005 | extended entity data database handle |
|------------|--------------------------------------------------|
| 1010, | extended entity data x, y, and z coordinates |
| 1020, | |
| 1030 | |
|------------|--------------------------------------------------|
| 1011, | extended entity data x, y, and z coordinates of |
| 1021, | 3d world space position |
| 1031 | |
|------------|--------------------------------------------------|
| 1012, | extended entity data x, y, and z components of |
| 1022, | 3d world space displacement |
| 1032 | |
|------------|--------------------------------------------------|
| 1013, | extended entity data x, y, and z components of |
| 1023, | 3d world space direction |
| 1033 | |
|------------|--------------------------------------------------|
| 1040 | extended entity data floating-point value |
|------------|--------------------------------------------------|
| 1041 | extended entity data distance value |
|------------|--------------------------------------------------|
| 1042 | extended entity data scale factor |
|------------|--------------------------------------------------|
| 1070 | extended entity data 16-bit signed integer |
|------------|--------------------------------------------------|
| 1071 | extended entity data 32-bit signed long |
+---------------------------------------------------------------+
|
