dxf.htm

各种文件格式说明及程序描述

the count in the 70 group as an index to read in the table.  it is provided
so that your program to read dxf files can allocate an array in advance
large enough to hold all the table entries that follow.</pre>
    <pre>following this header for each table are the table entries.  each table
item consists of a 0 group identifying the item type (same as table name,
e.g., &quot;ltype&quot; or &quot;layer&quot;), a 2 group giving the name of the table entry, a
70 group specifying flags relevant to the table entry (defined for each
table below), and additional groups that give the value of the table entry.
the end of each table is indicated by a 0 group with the value &quot;endtab&quot;.</pre>
    <pre>if any table entry has bit value 64 set in its group 70 flags, the table
entry was referenced by at least one entity in the drawing the last time
the drawing editor was entered to edit this drawing.  this &quot;referenced&quot;
flag is for the benefit of the purge command; 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>  ltype    3 (descriptive text for linetype), 72 (alignment code), 73
           (number of dash length items), 40 (total pattern length), 49
           (dash length 1), 49 (dash length 2), . . .</pre>
    <pre>  layer    62 (color number, negative if layer is off), 6 (linetype
           name).  the 1 bit is set in the 70 group flags if the layer is
           frozen.</pre>
    <pre>  style    40 (fixed text height; 0 if not fixed), 41 (width factor), 50
           (obliquing angle), 71 (text generation flags), 42 (last height
           used), 3 (primary font file name), 4 (&quot;bigfont&quot; file name;
           blank if none).  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 file name) is meaningful
           (all the other groups are output, however).</pre>
    <pre>           the &quot;text generation flags&quot; are a bit-coded field with the
           following bit meanings:</pre>
    <pre>                flag bit value                meaning
                       2        text is backwards (mirrored in x)
                       4        text is upside down (mirrored in y)



</pre>
    <pre>10
&#12;                                   (c) drawing interchange and file formats</pre>
    <pre>  view     40 and 41 (view height and width), 10 and 20 (view center
           point), 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
           appendix a).</pre>
    <pre>  ucs      10, 20, 30 (origin), 11, 21, 31 (x axis direction), 12, 22, 32
           (y axis direction).  all in world coordinates.</pre>
    <pre>  vport    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), 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), 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 view-
           port configuration all have the name &quot;*active&quot;.  the first
           such entry describes the current viewport.</pre>
    <pre>  dwgmgr   for future use.  fields not yet defined.
</pre>
    <pre>c.1.5.3  blocks section</pre>
    <pre>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 &quot;anonymous&quot; 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 below, so refer to
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).
</pre>
    <pre>c.1.5.4  entities section</pre>
    <pre>entity items appear in both the block and entities sections of the dxf
file.  the appearance of entities in the two sections is identical, with
the exception that entities in the block section never have handles. 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</pre>
    <pre>                                                                         11
&#12;autocad reference manual</pre>
    <pre>discussion, groups that always occur are given by their group number and
function, while optional groups are indicated by &quot;-optional n&quot; following
the group description.  &quot;n&quot; 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 data-
base, and that as autocad is further enhanced, new groups will be added to
entities to accommodate additional features.  writing your dxf processing
program in a table-driven way, making no assumptions about the order of
groups in an entity, and ignoring any groups not presently defined, will
make it much easier to accommodate dxf files from future releases of
autocad.</pre>
    <pre>each entity begins with a 0 group identifying the entity type.  the names
used for the entities are given in the table that follows.  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. if handles are enabled, every entity has a
5 group containing its handle (as a string representing a hexadecimal
number). the following groups are included only if the entity has nonde-
fault values for these properties.</pre>
    <pre>  group code                         meaning
       6      linetype name (if not &quot;bylayer&quot;).  the special name &quot;byblock&quot;
              indicates a floating linetype.</pre>
    <pre>      38      elevation (if nonzero).  output only if system variable
              flatland is 1.  otherwise, z coordinates are supplied as
              3x-groups as part of each of the entity's defining points.</pre>
    <pre>      39      thickness (if nonzero).</pre>
    <pre>      62      color number (if not &quot;bylayer&quot;).  zero indicates the
              &quot;byblock&quot; (floating) color.</pre>
    <pre>     210,     these groups are included for each line, point, circle, shape,
     220,     text, arc, trace, solid, block reference, polyline, dimension,
     230      attribute, and attribute definition entity if its extrusion
              direction is not parallel to the world z axis.  the 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 below.
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 descrip-
tions, the term &quot;bit-coded&quot; 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 these fields and set to zero
when constructing a dxf file.</pre>
    <pre>12
&#12;                                   (c) drawing interchange and file formats</pre>
    <pre>  line      10, 20, 30 (start point), 11, 21, 31 (end point).</pre>
    <pre>  point     10, 20, 30 (point), 50 (angle of x axis for the ucs in effect
            when the point was drawn -optional 0, for use when pdmode is
            nonzero).</pre>
    <pre>  circle    10, 20, 30 (center), 40 (radius).</pre>
    <pre>  arc       10, 20, 30 (center), 40 (radius), 50 (start angle), 51 (end
            angle).</pre>
    <pre>  trace     four points defining the corners of the trace: (10, 20, 30),
            (11, 21, 31), (12, 22, 32), and (13, 23, 33).</pre>
    <pre>  solid     four points defining the corners of the solid: (10, 20, 30),
            (11, 21, 31), (12, 22, 32), and (13, 23, 33).  if only three
            points were entered (forming a triangular solid), the third
            and fourth points will be the same.</pre>
    <pre>  text      10, 20, 30 (insertion point), 40 (height), 1 (text value), 50
            (rotation angle -optional 0), 41 (relative x scale factor
            -optional 1), 51 (obliquing angle -optional 0), 7 (text style
            name -optional &quot;standard&quot;), 71 (text generation flags
            -optional 0), 72 (justification type -optional 0), 11, 21, 31
            (alignment point -optional, appears only if 72 group is
            present and nonzero).</pre>
    <pre>            the &quot;text generation flags&quot; are a bit-coded field with mean-
            ings as follows:</pre>
    <pre>                 flag bit value                meaning
                       2         text is backwards (mirrored in x)
                       4         text is upside down (mirrored in y)</pre>
    <pre>            the &quot;justification type&quot; value (not bit-coded) indicates the
            text justification style used on this entity, as shown in the
            following table.</pre>
    <pre>              value                       meaning
                0    text is left justified
                1    text is centered along its baseline
                2    text is right justified
                3    text is aligned between two points (height varies)
                4    text is &quot;middle&quot; (fully) centered
                5    text is fit between two points (width varies)</pre>
    <pre>            if the justification is anything other than 0 (left justi-
            fied), 11, 21, and 31 groups will also appear in the entity
            to specify the alignment point of the text (center, right-
            most, or second alignment point).</pre>
    <pre>            dxfout handles ascii control characters in text strings by
            expanding the character into a &quot;^&quot; (caret) followed by the</pre>
    <pre>                                                                         13
&#12;autocad reference manual</pre>
    <pre>            appropriate letter.  for example, an ascii control-g (bel,
            decimal code 7) is output as &quot;^g&quot;.  if the text itself con-
            tains a caret character, it is expanded to &quot;^ &quot; (caret,
            space).  dxfin performs the complementary conversion.</pre>
    <pre>  shape     10, 20, 30 (insertion point), 40 (size), 2 (shape name), 50
            (rotation angle -optional 0), 41 (relative x scale factor
            -optional 1), 51 (obliquing angle -optional 0).</pre>
    <pre>  block     2 (block name), 70 (block type flags), 10, 20, 30 (block base
            point).  appears only in blocks section.  the &quot;block type
            flags&quot; are bit-coded, with the following bit meanings:</pre>
    <pre>              flag bit value                   meaning
                    1         this is an &quot;anonymous&quot; block generated by
                              hatching, associative dimensioning, or
                              other internal operations.
                    2         this block has attributes.</pre>
    <pre>  endblk    no groups.  appears only in blocks section.</pre>
    <pre>  insert    66 (&quot;attributes follow&quot; flag -optional 0), 2 (block name),
            10, 20, 30 (insertion point), 41 (x scale factor -optional
            1), 42 (y scale factor -optional 1), 43 (z scale factor
            -optional 1), 50 (rotation angle -optional 0), 70 and 71
            (column and row counts -optional 1), 44 and 45 (column and
            row spacing -optional 0).</pre>
    <pre>            if the value of the &quot;attributes follow&quot; flag is 1, a series
            of attribute (attrib) entities is expected to follow the
            insert, terminated by a sequence end (seqend) entity.</pre>
    <pre>  attdef    10, 20, 30 (text start), 40 (text height), 1 (default value,
            see text above for handling of ascii control characters), 3
            (prompt string), 2 (tag string), 70 (attribute flags), 73
            (field length -optional 0), 50 (text rotation -optional 0),
            41 (relative x scale factor -optional 1), 51 (obliquing angle
            -optional 0), 7 (text style name -optional &quot;standard&quot;), 71
            (text generation flags -optional 0, see text above), 72 (text
            justification type -optional 0, see text above)), 11, 21, 31
            (alignment point -optional, appears only if 72 group is
            present and nonzero).</pre>
    <pre>            the &quot;attribute flags&quot; are a bit-coded field in which the bits
            have the following meanings:</pre>
    <pre>              flag bit value                   meaning
                    1         attribute is invisible (does not display)
                    2         this is a constant attribute
                    4         verification is required on input of this
                              attribute.
                    8         attribute is preset (no prompt during
                              insertion)</pre>
    <pre>14