Extended
data (xdata) is created by AutoLISP or ObjectARX applications. If an
entity contains extended data, it follows the entity's normal definition data.
The group codes 1000 through 1071 describe extended data. The following
is an example of an entity containing extended data in DXF format.
Normal entity definition data:
0
INSERT
5
F11
100
AcDbEntity
8
TOP
100
AcDbBlockReference
2
BLOCK_A
10
0.0
20
0.0
30
0.0
Extended entity definition data:
1001
AME_SOL
1002
{1070
0
1071
1.95059E+06
1070
519
1010
2.54717
1020
2.122642
1030
2.049201
1005
ECD
1005
EE9
1005
0
1040
0.0
1040
1.0
1000
MILD_STEEL
The
group code 1001 indicates the beginning of extended data. In contrast to
normal entity data, with extended data the same group code can appear multiple
times, and order is important.
Extended data is grouped by registered application
name. Each registered application group begins with a 1001 group
code, with the application name as the string value. Registered
application names correspond to APPID symbol table entries.
An application can use as many APPID names as
needed. APPID names are permanent, although they can be purged if
they aren't currently used in the drawing. Each APPID name can have
no more than one data group attached to each entity. Within an application
group, the sequence of extended data groups and their meaning is
defined by the application.
The extended data
group codes are listed in the following table.
Extended
data group codes and descriptions
|
Entity
name
|
Group code
|
Description
|
String
|
1000
|
Strings
in extended data can be up to 255 bytes long (with the 256th byte
reserved for the null character)
|
Application
name
|
1001 also a
string value
|
Application
names can be up to 31 bytes long (the 32nd byte is reserved for
the null character)
NoteDo
not add a 1001 group into your extended data because AutoCAD assumes
it is the beginning of a new application extended data group
|
Control
string
|
1002
|
An extended
data control string can be either “{”or “}”.
These braces enable applications to organize their data by subdividing the
data into lists. The left brace begins a list, and the right brace terminates
the most recent list. Lists can be nested
When AutoCAD reads
the extended data for a particular application, it checks to ensure
that braces are balanced
|
Layer name
|
1003
|
Name of
the layer associated with the extended data
|
Binary
data
|
1004
|
Binary
data is organized into variable-length chunks. The maximum
length of each chunk is 127 bytes. In ASCII DXF files, binary data
is represented as a string of hexadecimal digits, two per binary
byte
|
Database
handle
|
1005
|
Handles
of entities in the drawing database
NoteWhen a drawing with handles and extended
data handles is imported into another drawing using INSERT, INSERT
*, XREF Bind, XBIND, or partial OPEN, the extended data handles
are translated in the same manner as their corresponding entity handles,
thus maintaining their binding. This is also done in the EXPLODE
block operation or for any other AutoCAD operation. When AUDIT
detects an extended data handle that doesn't match the handle of
an entity in the drawing file, it is considered an error. If AUDIT
is fixing entities, it sets the handle to 0
|
3 reals
|
1010, 1020, 1030
|
Three real
values, in the order X, Y, Z.
They can be used as a point or vector record. AutoCAD never alters
their value
|
World space
position
|
1011, 1021, 1031
|
Unlike
a simple 3D point, the world space coordinates are moved, scaled,
rotated, and mirrored along with the parent entity to which the
extended data belongs. The world space position is also stretched
when the STRETCH command is applied to the parent entity and this
point lies within the select window
|
World space displacement
|
1012, 1022, 1032
|
Also a
3D point that is scaled, rotated, and mirrored along with the parent
(but is not moved or stretched)
|
World direction
|
1013, 1023, 1033
|
Also a
3D point that is rotated and mirrored along with the parent (but
is not moved, scaled, or stretched)
|
Real
|
1040
|
A real
value
|
Distance
|
1041
|
A real
value that is scaled along with the parent entity
|
Scale factor
|
1042
|
Also a
real value that is scaled along with the parent. The difference
between a distance and a scale factor is application-defined
|
Integer
|
1070
|
A 16-bit
integer (signed or unsigned)
|
Long
|
1071
|
A 32-bit
signed (long) integer
|
