dxf.htm

刚刚看到本站有Visual C++数字图象处理（人民邮电出版社）的电子书

</pre>
    <pre>c.1.5  file sections</pre>
    <pre>the dxf file is subdivided into four sections.  file separator groups are
used to delimit these file sections.  the following is an example of a void
dxf file with only the section markers and table headers present.</pre>
    <pre>      0                           (begin header section)
    section
      2
    header
        &lt;&lt;&lt;&lt;header variable items go here&gt;&gt;&gt;&gt;
      0
    endsec                        (end header section)
      0                           (begin tables section)
    section
      2</pre>
    <pre>                                                                          5
&#12;autocad reference manual</pre>
    <pre>    tables
      0
    table
      2
    vport
     70
    (viewport table maximum item count)
        &lt;&lt;&lt;&lt;viewport table items go here&gt;&gt;&gt;&gt;
      0
    endtab
      0
    table
      2
    ltype, layer, style, view, ucs, or dwgmgr
     70
    (table maximum item count)
        &lt;&lt;&lt;&lt;table items go here&gt;&gt;&gt;&gt;
      0
    endtab
      0
    endsec                        (end tables section)
      0                           (begin blocks section)
    section
      2
    blocks
        &lt;&lt;&lt;&lt;block definition entities go here&gt;&gt;&gt;&gt;
      0
    endsec                        (end blocks section)
      0                           (begin entities section)
    section
      2
    entities
        &lt;&lt;&lt;&lt;drawing entities go here&gt;&gt;&gt;&gt;
      0
    endsec                        (end entities section)
      0
    eof                           (end of file)
</pre>
    <pre>c.1.5.1  header section</pre>
    <pre>the header section of the dxf file contains settings of variables
associated with the drawing.  these variables are set with various commands
and are the type of information displayed by the status command.  each
variable is specified in the header section by a 9 group giving its name,
followed by groups that supply its value.  the header variables, the groups
that follow, and their meanings are listed below.</pre>
    <pre>although this list is very similar to the list of system variables in
appendix a, the two lists are not identical.  be sure you're referring to
the proper list.

</pre>
    <pre>6
&#12;                                   (c) drawing interchange and file formats</pre>
    <pre>  $acadver       1     the autocad drawing database version number.
  $angbase      50     angle 0 direction.
  $angdir       70     1=clockwise angles, 0=counterclockwise.
  $attdia       70     attribute entry dialogues, 1 = on, 0 = off
  $attmode      70     attribute visibility: 0=none, 1=normal, 2=all.
  $attreq       70     attribute prompting during insert, 1 = on, 0 = off
  $aunits       70     units format for angles.
  $auprec       70     units precision for angles.
  $axismode     70     axis on if nonzero.
  $axisunit   10,20    axis x and y tick spacing.
  $blipmode     70     blip mode on if nonzero.
  $cecolor      62     entity color number; 0 = byblock, 256 = bylayer.
  $celtype       6     entity linetype name, or byblock or bylayer.
  $chamfera     40     first chamfer distance.
  $chamferb     40     second chamfer distance.
  $clayer        8     current layer name.
  $coords       70     0=static coordinate display, 1=continuous update,
                       2=&quot;d&lt;a&quot; format.
  $dimalt       70     alternate unit dimensioning performed if nonzero.
  $dimaltd      70     alternate unit decimal places.
  $dimaltf      40     alternate unit scale factor.
  $dimapost      1     alternate dimensioning suffix
  $dimaso       70     1=create associative dimensioning, 0=draw
                       individual entities.
  $dimasz       40     dimensioning arrow size.
  $dimblk        2     arrow block name.
  $dimblk1       1     first arrow block name.
  $dimblk2       1     second arrow block name.
  $dimcen       40     size of center mark/lines.
  $dimdle       40     dimension line extension.
  $dimdli       40     dimension line increment.
  $dimexe       40     extension line extension.
  $dimexo       40     extension line offset.
  $dimlfac      40     linear measurements scale factor.
  $dimlim       70     dimension limits generated if nonzero.
  $dimpost       1     general dimensioning suffix
  $dimrnd       40     rounding value for dimension distances.
  $dimsah       70     use separate arrow blocks if nonzero.
  $dimscale     40     overall dimensioning scale factor.
  $dimse1       70     first extension line suppressed if nonzero.
  $dimse2       70     second extension line suppressed if nonzero.
  $dimsho       70     1=recompute dimensions while dragging,
                       0=drag original image.
  $dimsoxd      70     suppress outside-extensions dimension lines
                       if nonzero.
  $dimtad       70     text above dimension line if nonzero.
  $dimtih       70     text inside horizontal if nonzero.
  $dimtix       70     force text inside extensions if nonzero.
  $dimtm        40     minus tolerance.
  $dimtofl      70     if text outside extensions, force line between
                       extensions if nonzero.
  $dimtoh       70     text outside horizontal if nonzero.
</pre>
    <pre>                                                                          7
&#12;autocad reference manual</pre>
    <pre>  $dimtol       70     dimension tolerances generated if nonzero.
  $dimtp        40     plus tolerance.
  $dimtsz       40     dimensioning tick size: 0=no ticks.
  $dimtvp       40     text vertical position.
  $dimtxt       40     dimensioning text height.
  $dimzin       70     zero suppression for &quot;feet &amp; inch&quot; dimensions.
  $dragmode     70     0=off, 1=on, 2=auto.
  $elevation    40     current elevation set by elev command.
  $extmax    10,20,30  xy drawing extents upper right corner (in wcs).
  $extmin    10,20,30  xy drawing extents lower left corner (in wcs).
  $filletrad    40     fillet radius.
  $fillmode     70     fill mode on if nonzero.
  $flatland     70     force compatibility with older versions if nonzero.
  $handling     70     handles enabled if nonzero.
  $handseed      5     next available handle.
  $insbase   10,20,30  insertion base set by base command (in wcs).
  $limcheck     70     nonzero if limits checking is on.
  $limmax     10,20    xy drawing limits upper right corner (in wcs).
  $limmin     10,20    xy drawing limits lower left corner (in wcs).
  $ltscale      40     global linetype scale.
  $lunits       70     units format for coordinates and distances.
  $luprec       70     units precision for coordinates and distances.
  $menu          1     name of menu file.
  $mirrtext     70     mirror text if nonzero.
  $orthomode    70     ortho mode on if nonzero.
  $osmode       70     running object snap modes.
  $pdmode       70     point display mode.
  $pdsize       40     point display size.
  $plinewid     40     default polyline width.
  $qtextmode    70     quick text mode on if nonzero.
  $regenmode    70     regenauto mode on if nonzero.
  $sketchinc    40     sketch record increment.
  $skpoly       70     0=sketch lines, 1=sketch polylines.
  $splframe     70     spline control polygon display, 1 = on, 0 = off.
  $splinesegs   70     number of line segments per spline patch.
  $splinetype   70     spline curve type for &quot;pedit spline&quot;
                       (see appendix a).
  $surftab1     70     number of mesh tabulations in first direction.
  $surftab2     70     number of mesh tabulations in second direction.
  $surftype     70     surface type for &quot;pedit smooth&quot; (see appendix a).
  $surfu        70     surface density (for &quot;pedit smooth&quot;) in m direction.
  $surfv        70     surface density (for &quot;pedit smooth&quot;) in n direction.
  $tdcreate     40     date/time of drawing creation.
  $tdindwg      40     cumulative editing time for this drawing.
  $tdupdate     40     date/time of last drawing update.
  $tdusrtimer   40     user elapsed timer.
  $textsize     40     default text height.
  $textstyle     7     current text style name.
  $thickness    40     current thickness set by elev command.
  $tracewid     40     default trace width.
  $ucsname       1     name of current ucs.
  $ucsorg    10,20,30  origin of current ucs (in wcs).
</pre>
    <pre>8
&#12;                                   (c) drawing interchange and file formats</pre>
    <pre>  $ucsxdir   10,20,30  direction of current ucs's x axis
                       (in world coordinates).
  $ucsydir   10,20,30  direction of current ucs's y axis
                       (in world coordinates).
  $useri1 - 5   70     five integer variables intended for use by
                       third-party developers.
  $userr1 - 5   40     five real variables intended for use by
                       third-party developers.
  $usrtimer     70     0=timer off, 1=timer on.
  $worldview    70     1=set ucs to wcs during dview/vpoint,
                       0=don't change ucs</pre>
    <pre>the header variables listed below existed prior to autocad release 10 but
now have independent settings for each active viewport.  they are not
output by dxfout unless system variable flatland is set to 1.  dxfin honors
these variables when read from dxf files, but if a vport symbol table with
&quot;*active&quot; entries is present (as is true for any dxf file produced by
release 10 or higher), the values in the vport table entries will override
the values of these header variables.</pre>
    <pre>  $fastzoom     70     fast zoom enabled if nonzero.
  $gridmode     70     grid mode on if nonzero.
  $gridunit   10,20    grid x and y spacing.
  $snapang      50     snap grid rotation angle.
  $snapbase   10,20    snap/grid base point (in ucs).
  $snapisopair  70     isometric plane: 0=left, 1=top, 2=right.
  $snapmode     70     snap mode on if nonzero.
  $snapstyle    70     snap style: 0=standard, 1=isometric.
  $snapunit   10,20    snap grid x and y spacing.
  $viewctr    10,20    xy center of current view on screen.
  $viewdir   10,20,30  viewing direction (direction from target, in wcs).
  $viewsize     40     height of view.</pre>
    <pre>the date/time variables ($tdcreate and $tdupdate) are output as real num-
bers in the format:</pre>
    <pre>    &lt;julian date&gt;.&lt;fraction&gt;</pre>
    <pre>the elapsed time variables ($tdindwg and $tdusrtimer) have a similar
format:</pre>
    <pre>    &lt;number of days&gt;.&lt;fraction&gt;
</pre>
    <pre>c.1.5.2  tables section</pre>
    <pre>the tables section contains several tables, each of which in turn contains
a variable number of table entries. the order of the tables may change, but
the ltype table will always precede the layer table.  each table is intro-