Shareware Overload Trio 2/Shareware Overload Trio Volume 2 (Chestnut CD-ROM).ISO/dir30/eerems11.zip/EEREM.DOC

Text File | 1994-08-09 | 16KB | 416 lines

Documentation for Extra Entity REMoval version 1.0         August 7, 1994

Jon Fleming CIS 70334,2443

WHAT IS EEREM?

       EEREM is a package written in C for the AutoCAD ADS environment.
   It removes a large set of possible "extra entities" from an AutoCAD
   drawing.  An "extra entity" is one which adds no information to the
   drawing, such as duplicate lines.  Extra entities can arise from many
   situations.  One situation that can give rise to MANY extra entities
   is projecting a 3D wireframe model into 2D with PROJECT.LSP (included
   with AutoCAD) or the equivalent.
       Extra entities are inconvenient because they increase drawing file
   size, lead to unexpected OSNAP results, and cause clogging of pens in
   pen plotters forced to trace the same path several times.

BOILERPLATE

       EEREM is public domain.  You may do what you want with it; please
   credit me if you use the code or any significant portion of it in
   your programs.
       I expect EEREM to do what it is described as doing.  However,
   EEREM is supplied "as-is" with no warranty of mercantability or
   fitness for a particular purpose.  I accept no responsibility for its
   operation or damages of any kind.
       If you bring problems to my attention, I will do what I can to
   resolve them.

WHAT DO I NEED TO USE EEREM?

       This incarnation of EEREM has been tested under AutoCAD Release
   12 c3 DOS and AutoCAD Release 12 c4 Windows. It may run under higher
   release numbers, I cannot determine that at this time.  If
   appropriately compiled, it _should_ run on other platforms.

       For some reason I don't understand, EEREM does not work as well
   on polylines under Windows as it does under DOS.

       EEREM will NOT work under AutoCAD Release 11 or previous.

       WARNING:  Although I cannot prove it, I think that earlier
   releases of AutoCAD 12 had bugs in the ads_ssget() "X" interface which
   led to EEREM missing many entities it should delete.  If EEREM does
   not do the job for you, and you are running an older release of R12,
   upgrade to the current release.

HOW DO I USE EEREM?

       First, copy EEREM.EXP and EEREM.DCL into a directory (or
   directories) that is (are) listed in the AutoCAD "ACAD" environment
   variable.

       EEREM must be loaded into memory.  At the AutoCAD "Command:"
   prompt, you may type:

   (xload "eerem")

   (note:  once you have loaded EEREM, you need not do it again until you
   have exited and re-entered AutoCAD.  This is different from LISP
   programs which you must load every time you move from one drawing to
   another without exiting AutoCAD).

       Once EEREM is loaded, at the AutoCAD "Command:" prompt, type:

   ddeerem

   Then click on the "Select Entities for Checking" button, select a set
   of entities to check, and click on the OK button.

       See "ADVANCED EEREM USAGE", below, for hints and suggestions on
   how to use EEREM efficiently; explanations of the other items in the
   dialog box; and using EEREM from your own AutoLISP or C program.

WHAT ENTITIES DOES EEREM REMOVE?

       First, a pair of definitions:

   duplicate entity = an entity that covers EXACTLY the same extents as
                      another entity.

   underlying entity = an entity that DOES NOT cover exactly the same
                       extents as another entity but is completely
                       covered by that other entity.

   For example, if there's a line from (0,0,0) to (1,0,0), then another
   line from (0,0,0) to (1,0,0) is a DUPLICATE entity.  Lines from (for
   example) (0,0,0) to (0,0,0) or from (0.25,0,0) to (0.75,0,0) are
   UNDERLYING entities.

       Briefly (see "DETAILED ENTITY REMOVAL SPECIFICATIONS", below, for
   more detail), EEREM removes:

   All line duplicates and lines that underlie other lines (including
       "zero-length" lines if they underlie a non-zero-length line).

   All circle duplicates and arcs that underlie circles (circles
       underlying circles are duplicate circles!).

   All arc duplicates and arcs that underlie arcs.

   All duplicate points (points underlying points are the same as
       duplicate points!)

   Most 2D and 3D (but not mesh) polyline duplicates and most 2D and 3D
       (but not mesh) polylines that underlie other 2D and 3D (but not
       mesh) polylines

WHAT COMMON EXTRA ENTITIES ARE _NOT_ REMOVED?

       Different-type entities, such as polylines underlying lines.
   (such entities are often created by PROJECT.LSP; all versions that
   I've examined project all circles and arcs as polylines even when a
   line or arc or circle would be more appropriate.  I haven't examined
   the Release 12 PROJECT.LSP).

       Entities that appear to overlay each other on the screen but are
   actually far enough apart for EEREM to consider them different.

       Entities that overlap, but neither entity completely covers the
   other.

HINTS

        EEREM will run _much_ more slowly if there are a lot of entities
   in the drawing that are not involved in EEREM's operation.  This is
   because EEREM asks AutoCAD to search the entire drawing database for
   entities that may be deleted, and does so many times.  (Other
   algorithms that I thought of proved to be much slower in 99% of the
   cases).
        Always run EEREM in a drawing that contains as few entities as
   possible.  The AutoCAD WBLOCK command is often useful for creating
   temporary drawings on which to run EEREM.

ADVANCED EEREM USAGE:  EASY LOADING

       AutoCAD Release 12 includes a sophisticated automatic loading
   facility for command-line-callable functions.  To activate this, if
   you DO NOT have an S::STARTUP function in ACAD.LSP, add the following
   to ACAD.LSP:

   (defun S::STARTUP ()
     (autoxload "EEREM" '("DDEEREM"))
   )

   If you already have a S::STARTUP function in ACAD.LSP, add the
   following to it:

     (autoxload "EEREM" '("DDEEREM"))

       For usage from AutoLISP, the following works:

     (if eerem
       (eerem sel_set)
       (if (xload "EEREM")
         (eerem sel_set)
         (prompt "\nCan't locate EEREM.EXP!")
       )
     )

ADVANCED EEREM USAGE:  FROM THE "COMMAND:" PROMPT

       I hope the three check boxes at the top of the dialog box are
   self-explanatory.  For example, say there's a line from (0,0,0) to
   (1,0,0) on layer "0", and another line from (0,0,0) to (1,0,0) on
   layer "DUMMY".  If the "Entities on different layers are different"
   check box IS NOT checked, EEREM will remove one of these entites
   (which one depends on their order in the set of entities selected for
   checking).  If the "Entities on different layers are different" check
   box IS checked, EEREM will not remove either entity.  The other two
   check boxes behave in an analogous fashion.

       There is one aspect that may be counterintuitive.  The colors or
   linetypes BYLAYER or BYBLOCK are always considered different from an
   explicit color or linetype.  For example, say there are two lines that
   are identical in every respect, including what layer they are on,
   except one has color BYLAYER and one has color YELLOW.  Say also that
   the default color of the layer is YELLOW.  The two lines appear
   identical on screen, but if the "Entities with different colors are
   different" checkbox is checked EEREM will _not_ remove either line.

       You probably don't want to change the "Tolerance" value, but you
   can try it if you want.  Briefly, the tolerance is a measure of how
   far apart points must be before EEREM considers them unequal (see
   "DETAILED ENTITY REMOVAL SPECIFICATIONS", below, for more
   explanation).  The tolerance is in drawing units.

ADVANCED EEREM USAGE:  FROM AUTOLISP

       The dialog box version of EEREM may be called from AutoLISP by:

   (ddeerem)

   There is no return value.

       To call the EEREM core engine without putting up a dialog box,
   use:

   (eerem sel_set checklayer checkltype checkcolor tolerance)

   where:

       sel_set is a selection set of entities to check, and is required.

       checklayer is NIL to count entities on different layers as the same,
       non-NIL to count entities on different layers as different.  checklayer
       is optional (default NIL) unless one or more of the following arguments
       are supplied.

       checkltype is NIL to count entities with different linetypes as the
       same, non-NIL to count entities with different linetypes as different.
       checkltype is optional (default NIL) unless one or more of the
       following arguments are supplied.

       checkcolor is NIL to count entities with different colors as the same,
       non-NIL to count entities with different colors as different.
       checkcolor is optional (default NIL) unless one or more of the
       following arguments are supplied.

       tolerance is a real number that measures how close points must be to
       be considered the same (well, approximately; see "DETAILED ENTITY
       REMOVAL SPECIFICATIONS", below, for more detail).  tolerance is
       optional.  The default is 0.00001.

   (eerem ...) returns NIL if an error was detected or T otherwise.

ADVANCED EEREM USAGE:  FROM ADS

       Call ddeerem through ads_invoke().  The return values are RSRSLT
   (no error detected) or RSERR (can't find DCL file).

       Call eerem through ads_invoke() with a list corresponding to the
   AutoLISP parameters.  The return values are RSRSLT (corresponding to
   the AutOLISP "T" return values, above) or RSERR (corresponding to the
   AutoLISP "NIL" return values, above).

       I haven't tested this.

DETAILED ENTITY REMOVAL SPECIFICATIONS:  GENERAL

       All entity removal is based on a "current" entity and a
   "candidate" entity.  The current entity is one of the set of entities
   that was selected for extra entity removal, and must be a LINE,
   non-mesh POLYLINE, CIRCLE, ARC, or POINT.  Other entity types, in the
   set of entities selected for extra entity removal, are skipped.  The
   candidate is the same type of entity as the current entity but MAY OR
   MAY NOT be in the set of entities selected for extra entity removal;
   all possible candidates in the drawing are checked.  The candidate is
   the entity which will be deleted if it meets the criteria listed in
   the following sections.

       All combinations of current and candidate entities are checked.
   Most of the filtering of candidate entities is done through the
   ads_ssget() "X" mechanism, yielding a (usually) small set of
   candidate entities that require further checking.  I think it is a
   failure of the ads_ssget "X" mechanism to return the proper set of
   entities that makes EEREM work improperly in early versions of R12
   when the viewpoint is not "plan UCS".

       Note that entity thickness IS NEVER CHECKED; if two entities are
   the same except for thickness, one of them will be removed!

       The following sections do not discuss whether or not the current
   and candidate entity's layer, color, or linetype matter.  If the
   appropriate flag(s) is(are) set, through the dialog box or through a
   parameter to the function, unsuitable candidates are filtered out by
   ads_ssget() "X".

DETAILED ENTITY REMOVAL SPECIFICATIONS:  LINES

       The candidate line is deleted if both its endpoints lie within a
   cylinder of radius "tolerance", centered on the current line and the
   same length as the current line.

       Lines shorter than 0.0001 times "tolerance" are not considered as
   "current" entities, because the algorithm blows up for coincident
   current line endpoints.  The presumption is that such short (or even
   zero-length) lines are extremely likely to be underlying some other
   line.

DETAILED ENTITY REMOVAL SPECIFICATIONS: CIRCLES & UNDERLYING ARCS

       When the current entity is a circle, a candidate circle or arc is
   deleted if:

   its center lies within a cube of side two times "tolerance", centered
   on the center of the current circle

       AND

   the candidate's radius is within plus or minus "tolerance" of the
   current circle's radius

       AND

   the distance from the tip of the candidate's extrusion vector to
   EITHER the tip of the current circle's extrusion vector OR the tip of
   a unit vector directly opposite the current circle's extrusion vector
   is less than "tolerance".

DETAILED ENTITY REMOVAL SPECIFICATIONS:  POINTS

       A candidate point is deleted if it lies within a cube of side two
   times "tolerance", centered on the current point entity.

DETAILED ENTITY REMOVAL SPECIFICATIONS:  ARCS

       When the current entity is an arc, a candidate arc is deleted if:

   its center lies within a cube of side two times "tolerance", centered
   on the center of the current arc

       AND

   the candidate's radius is within plus or minus "tolerance" of the
   current arc's radius

       AND

   the start and end points of the candidate arc are on or between the
   start and end points of the current arc

       AND

   the distance from the tip of the candidate's extrusion vector to
   EITHER the tip of the current arc's extrusion vector OR the tip of
   a unit vector directly opposite the current arc's extrusion vector
   is less than "tolerance".

DETAILED ENTITY REMOVAL SPECIFICATIONS:  POLYLINES

       Both the current and candidate polylines may not be 3D polygon
   meshes; such entities are skipped if they occur in the set of
   entities to check.

       Ready?  This is the BIG ONE!  Onward ...

       A candidate polyline is deleted if:

   its elevation is within plus or minus "tolerance" of the elevation of
   the current polyline

       AND

   the candidate's start and end widths are within plus or minus
   "tolerance" of the current polyline's start and end widths,
   respectively

       AND

   the candidate's polyline type and curve fit type are the same as the
   current polyline

       AND

   the distance from the tip of the candidate's extrusion vector to the
   tip of the current polyline's extrusion vector is less than
   "tolerance" (note that, unlike circles and arcs, polylines with
   extrusion vectors exactly opposite to that of the current polyline
   are not checked for deletion)

       AND

   for each successive vertex of the candidate, there is a vertex of the
   current polyline that:

       immediately follows the last current polyline vertex that matched
       the previous candidate polyline vertex

            AND

       matches the current candidate polyline vertex.


       In the above, "matches" means that:

   the distance from the candidate vertex to the current polyline vertex
   is less than "tolerance"

       AND

   the candidate vertex's start and end widths are within plus or minus
   "tolerance" of the current polyline vertex's start and end widths,
   respectively

       AND

   the candidate vertex's bulge factor is within plus or minus
   "tolerance" of the current polyline vertex's bulge factor

       AND

   the distance from the tip of the candidate vertex's tangent vector to
   the tip of the current polyline vertex's tangent vector is less than
   "tolerance"

       AND

   the current vertex's flag bits (group 70) are the same as the flag
   bits of the current polyline vertex.


   (Whoof!  That was almost as hard to write down precisely as it was to
   figure out!)

COMPILING EEREM:

       EEREM was compiled for DOS or Windows using Watcom C/C++-32 9.5.
   A .MAK file is included (in the source code package) for Watcom WMAKE.

       Hints:  be careful when asking the compiler to do agressive
   optimization; when I used "opmaxet" EEREM appeared to work but never
   removed any polylines.  Be sure to delete *>OBJ or TOUCH *.C when
   changing from compiling for Windows to compiling for DOS or vice
   versa.