Tech Arsenal 1/Tech Arsenal (Arsenal Computer).ISO/tek-01/3dkit1.zip/3DKIT.DOC

Text File | 1992-06-29 | 28KB | 595 lines

                TOOLS FOR 3-D WIREFRAME GRAPHICS
          ================================

                    May 1992

Hi!  I have been amazed by the good reception to my 3dv wireframe viewer
and by all the e-mail that it generated.  My ego was sufficiently massaged
to motivate me in producing a few tools for playing around with 3-D
wireframe objects.  These can be used in conjunction with 3dv, or on their
own.

3dv allows you to display 3-D objects on a PC screen, and rotate them in
real-time by moving the mouse.  It can be found, for example, in the
<MSDOS.GRAPHICS> directory of SIMTEL20, and in lots of other places.  Look
for 3DV25.ZIP (or .ZOO, etc).  It is FREE, and so are the goodies contained
here.

Digression --  For convenience, I give here the location of free and
shareware software in SIMTEL20.  See SIMTEL.DOC for info on how to get it.
Note that often new software versions are uploaded with slightly different
names; if you don't find a file try a directory listing.  There are many
other archive sites in the Internet, accessible through FTP and some
through e-mail servers.  For example, garbo.uwasa.fi, in Finland (e-mail
access instructions available by sending a 'send help' message, or a null
message, to [e-mail] with a subject line of
'garbo-request'.  Don't include the quotes '').  Much software is also
available from bulletin boards.  -- End of digression.

3dv uses a simple plain text file format, let's call it 3DV format, that I
am taking as a common format for 3-D wireframe objects (objects formed by
points and lines in three dimensions).  One of the programs, 3DVto2D, does
a perspective projection, like those displayed by 3dv, but with output to a
file that can later be plotted, printed, or whatever.  This output is an
ASCII list of 2-D points (a "2D list"), that will be our common format for
2-D pictures.  The idea is to have other tools that manipulate these files
or convert between these and other formats, a bit like what PBMPLUS does
for rasters.  I have written a few of these tools, included here with C
sources, to get the ball rolling.  I hope that others may take over.
Incidentally, the code in 3DVto2D may interest those who have asked, mostly
politely (funny the attitudes of some people), for source or hints on 3-D
transformations (I am not releasing the 3dv source for reasons explained in
the documentation of that package).

The main components of this kit are:

OFFto3DV  -  Converts from a format called OFF (Object File Format) to 3DV.
There are lots of nice 3-D objects in OFF format around the Internet. There
are also around programs to convert from other formats into OFF.  See
OBJECTS.DOC for more info on where to find them.

SHDto3DV  -  Converts from "shaded" format to 3DV.

XYZto3DV  -  XYZ is an interactive 3-D editor/builder written by Dale P.
Stocker to create objects for the SurfaceModel, Automove, and DKB raytracer
packages.  XYZto3DV (you gessed it!) converts XYZ output to 3DV format.

3DHELP  -  A C program written by Bruce Colletti to create 3DV files from
mathematical functions.  Source only, since you have to code and link your
function.  See 3DHELP.C for documentation.

3DMERGE  -  Combines two 3DV files into one.

SHRINK  -  Minimizes the size of 3DV files.  Facilitates converting objects
to 3DV format; you can use a straightforward and simple-minded approach and
let SHRINK to take care of efficiency.

3DVto2D  -  Projects a 3-D object in 3DV format into a plane, from a
user-specified viewpoint.  The output (2D list) can be directly
displayed/printed by GNUPLOT, a free scientific graphing program (good).

2DtoHPGL  -  Converts a 2D list to HPGL plotter instructions.  There are
utilities for printing HPGL on a variety of printers, and to convert it to
AutoCAD format, for example.

2DtoEXF  -  Converts 2D list to Evolution Computing's EXF format for
EasyCAD (and presumably FastCAD).  You can then use the CAD program to
modify the drawing to your heart's content.

The executables, for MSDOS, were compiled with Turbo C 2.0 using the
compact memory model.

There are also some 3-D object files (see ART.DOC), and a few example
GNUPLOT scripts and DOS batch files.


                  3DV FILE FORMAT
                  ---------------

It is a plain ASCII text file that contains a list of point coordinates,
followed by a list of move/draw instructions defining the lines in the
object.  It looks like this:

number_of_points
x1 y1 z1
x2 y2 z2
...
xn yn zn
number_of_move-draws
p1 c1
p2 c2
...
pm cm

The xi, yi, zi are the coordinates of each point, one set to a line,
separated by spaces.  Each pair (pj cj) means "draw a line to point number
pj using colour number cj".  The point numbers are the indices (origin 1)
of the points in the list of coordinates (e.g. "5" is the 5-th point in the
list).  The colour numbers are the usual IBM PC colour indices 1 to 15.  A
zero colour means "move" to the point without drawing (or drawing in the
background colour, if you prefer).  Multiple spaces do not matter.
Coordinate values can take any form accepted by C as a floating point
number, and the rest must be integers.  See the included *.3DV files for
examples.

Actually, 3dv and some of the tools do not care about line feeds and
carriage returns.  However, some processing (e.g. in 3DMERGE) is easier if
we always have one item per line, so let's stick to that.

In retrospect, it might have been a good idea to allow for comments
embedded in the file, but now it is too late.  We can add anything at the
end of the file, though.  I suggest including there object descriptions and
credits.

This format is fairly compact and convenient.  It is fine for wireframe
objects, but of course it does not include the topological information
about faces, etc., that would be needed for hidden line elimination, solid
modelling, or other uses.


                   2D LIST FORMAT
                   --------------

This is the output from 3DVto2D, and I propose it as a common format for
two-dimensional drawings.  It is simply one or more comment lines beginning
with #, followed by a list of coordinate pairs and colour information, with
implicit "draw" instructions and "moves" indicated by a blank line as well
as a colour equal to zero:

# ... x_range=[xmin:xmax] ... y_range=[ymin:ymax] ...
#...

xa ya ca
xb yb cb
...
xc yc cc

xd yd cd
xe ye ce
...
...
xt yt ct

xu yu cu
xv yv cv
...
xw yw cw

The x and y are the coordinate values (integers or reals), and the c are
colours (0 to 15).  A zero colour indicates a move, and must follow a blank
line; in the example, ca, cd, and cu must be zero.  At least for use in
2DtoHPGL without the /s option, somewhere in the first line (comment) we
must have the keywords x_range and y_range followed by bounds for the x and
y values in the format shown above (see the description of 3DVto2D, below,
for an example).  There is no compulsory line count; the data ends with the
end of file.  For examples see the output generated by 3DVto2D.

These files are compatible with the GNUPLOT graphing program, which can be
used with its default input parameters to display or print the drawing
(GNUPLOT will just ignore the third column containing the colours).
GNUPLOT is free and you can find it, for example, in SIMTEL20 as
<MSDOS.PLOT>GNUPLT32.ZIP .


                THE TOOLS IN DETAIL
                -------------------

Unless stated otherwise, if the names of the files to be processed are not
given on the command line then the standard input/output streams are used.
Thus, these tools can be used as filters, with DOS pipes or redirection.
For a simple example see Xto3.BAT .

Some of the tools accept optional command switches.  These can go in any
order, before the file names, if any.  Forms different from those shown
here might also work, I am not sure of the exact requirements of the public
domain getopt.c that I used.  In particular, you could use - as a switch
character instead of /, although you might run into trouble with minus
signs.  Try it at your own risk.

Much of this could probably have been done more elegantly (?) with AWK or
SED scripts.  With C, however, the tools are fast and self-contained.  I
wrote the code aiming at clarity ahead of efficiency.  For example, I used
mostly indexed arrays, instead of trying to be too clever with pointers.

In the syntax, below, brackets indicate optional items.  You get a similar
help message by running the program with /? or other invalid arguments.


                  OFFto3DV

Syntax:  OFFto3DV [/cn] [infile [outfile]]

Converts infile, in OFF ASCII Indexed_Poly format, into outfile, in 3DV
format.  The option /cn specifies n as the colour to be used; the default
is /c9.

The conversion is simple-minded.  Run the output through SHRINK to reduce
the file size.

OFF (Object File Format) objects may be specified with a set of several
files.  The Indexed_Poly "geometry" file, used by OFFto3DV, seems to be
(almost?) always present.  The convention is to use a file extension
".geom" for this, on machines that support long file extension names. Often
there is also a file with extension ".aoff", that contains object
information such as author, description, and copyright.  There may be other
files with data on colours, polygon normals, etc., which are ignored here.

These objects (or at least most of them) are formed by polygons.  The
Indexed_Poly file is somewhat similar to a 3DV file, with a list of vertex
coordinates followed by a list of polygons.  The first line has three
integers: the number of vertices, the number of polygons, and the total
number of edges.  Then comes the list of vertex coordinates, triples of
floating point numbers.  The polygons immediately follow, one per line.
These are specified by a list of integers, where the first is the number of
polygon vertices, and the others are the vertex indices in the coordinates
list.

See OBJECTS.DOC for sources of OFF objects, and of the full format
specification if you really want it.


                  SHDto3DV

Syntax:  SHDto3DV [/cn] [infile [outfile]]

Converts infile, in another common object format, explained below, into
outfile, in 3DV format.  The option /cn specifies n as the colour to be
used; the default is /c9.

The conversion is simple-minded.  Run the output through SHRINK to reduce
the file size.

I found a number of objects in this format on the Internet, for example in
hanauma.stanford.edu pub/graphics/Comp.graphics/objects/3d.  Initially I
thought that this was OFF, and wrote this converter.  It turned out that
this is slightly different.  In hanauma.stanford.edu
pub/graphics/Comp.graphics there is a file with the famous Sutherland
VolksWagen, where it is called "shaded" format, being used in a display
program called "shaded" running on SUN hardware.  The file contains AWK
scripts to convert the original VW data from a similar but more verbose
format into "shaded", and also the following note:

    The format for the "shaded" data files appears to be

    no_of_points    no_of_polygons
    minx maxy minz  maxx miny maxz
    x1 y1 z1
    x2 y2 z2
    ...
    xnp ynp znp
    no_of_corners point1 point2 point3 ... pointnc
    ...
    no_of_corners point1 point2 ... pointnc

    The point numbers are implicit, i.e. "5" refers to the fifth
    point in the list. See the file "socbal.dat" for an example.

This is the same as OFF, except for the extra second line with the ranges,
that we ignore, and the lack of an edges count, which forces reading all
the polygons in before starting to write the move/draw instructions.


                  XYZto3DV

Syntax:  XYZto3DV [infile [outfile]]

XYZ2 is an interactive 3-D editor/builder written by Dale P. Stocker to
create objects for the SurfaceModel, Automove, and DKB raytracer packages.
XYZto3DV converts the *.3DL file produced by XYZ2 into a 3DV file.  The
*.3DP and *.3DS files are not needed.

The conversion is simple-minded.  Run the output through SHRINK to reduce
the file size.

XYZ2 is free and can be found, for example, in SIMTEL20 as
<MSDOS.SURFMODL>XYZ21.ZIP .

Other 3-D editors that might be useful for designing objects are 3DMOD
(free, I found it somewhere in the Internet), and NORTHCAD (shareware,
<MSDOS.CAD>NCAD3D42.ZIP in SIMTEL20).  However, they do not include
documentation on their file formats.  3DMOD is (C) 1991 by Micah Silverman,
25 Pierrepoint Ave., Postdam, New York 13676, tel. [phone].


                  3DMERGE

Syntax:  3DMERGE infile1 [infile2 [outfile]]

Combines two 3DV files (infile1 and infile2) into one (outfile).  Note that
at least one input file is required in the command line.

The merging is simple-minded.  Run the output through SHRINK to reduce the
file size.

I wrote this mainly to put together the parts of the Sutherland VW from
hanauma (see above in SHDto3DV).  That was a waste of time, because there
was a full VW in "shaded" format somewhere else in hanauma, and in OFF
format in other places.  It might have other uses, though.  BTW, there is
an interesting photo in IEEE Computer Graphics & Applications, January
1987, p.8, showing Ivan Sutherland students digitizing the VW in 1971 using
paint, measuring tape, and rulers.


                   SHRINK

Syntax:  SHRINK [/on] [/tx] [/q] [infile [outfile]]

This is by far the most complex program of the lot.  It attempts to reduce
the size of a 3DV file in three steps:

1. Checks for (nearly) duplicated points.  Two points are considered the
same, and one of them dropped, if the absolute differences in all the three
coordinates are smaller than certain tolerance.  The tolerance is
calculated as the maximum coordinate range divided by x, where x is given
in the /t option.  The default is /t1e6.  Confused?  Forget it, just use
the default!

2. Checks for duplicated lines, including those resulting from deleting
(actually merging) points in step 1.  If two lines joining the same two
points have different colours, the colours are ORed.

3. Rearranges the move/draw instructions to eliminate as many moves as
possible.  This is a highly convoluted pointer chasing exercise, and I wont
try to explain how it works.  You may be able to follow the code, it is
reasonably well commented.

With the /o option you can restrict SHRINK to use only step 1 (/o1), 1 and
2 (/o2), or all three steps (/o3, the default).  Don't ask me why.  In any
case "obviously" redundant moves are omitted.

SHRINK can take a while on large files, so by default it outputs progress
messages to the standard error stream (usually the screen).  You can
suppress the messages with the /q (quiet) option.

This tool simplifies the writing of object generation, conversion, or
manipulation procedures.  Just do it the easy way, and let SHRINK take care
of the efficiency aspects.


                  3DVto2D

Syntax:  3DVto2D [/tx] [/nx] [/dx] [infile [outfile]]

Now, here is the answer to all those who asked for examples of code for 3-D
transformations!  It is also useful for high resolution display and
hard-copy.  Projects in perspective a 3-D object in 3DV format into a plane,
from a user-specified viewpoint.

To understand the specification of the viewpoint, think of the object as
enclosed by a box, and located at the centre of a sphere.  The box is just
large enough to contain the object, with sides parallel to the coordinate
axes.  The x axis goes from left to right, y from back to front, and z goes
up.  The box centre is at the centre of the sphere.  The viewpoint can be
anywhere on the sphere surface.  Its location is specified by latitude and
longitude in degrees, as on the surface of the Earth.  Latitude goes from
-90 at the South Pole, through 0 on the Equator, to 90 at the North Pole.
Zero longitude is at the front, increasing to the right; you can use any
positive or negative number which is interpreted modulo 360, i.e., plus or
minus 360 degrees brings you back to the front of the sphere.

This is the same system used in 3dv, where you move around the object by
changing longitude with left-right mouse movements, and latitude by moving
up-down.  You can use 3dv to choose a good viewpoint, noting the displayed
latitude/longitude values.  The /t option specifies the viewpoint laTitude,
and /n the loNgitude.  The defaults are zero.  For example,

    3DVto2D /t33.3 /n-60 thingy.3dv thingy.2d

would produce a view from a point at latitude 33.3 degrees (North) and
longitude -60 degrees (60 degrees West).

The /d option can be used to give the viewpoint distance, i.e. the sphere
radius.  A positive value is an absolute distance in user units, that is,
in the same units used for the points coordinates.  A /d0 is equivalent to
an infinite distance or, in other words, produces an orthogonal projection
(no perspective).  A minus sign indicates a multiple of the longest
diagonal of the bounding box (plus 1%, for compatibility with 3dv).  The
default is /d-3, identical to 3dv.

The output image is in 2D list format and, as already mentioned, can be
directly displayed/plotted/printed with GNUPLOT, or converted to other
formats.  The data is scaled is such a way that the image fits into a
square with corners (-1,-1) and (1,1), with the object bounding box centre
mapped into (0,0).  Some information is included in two lines of comments
at the beginning of the file, like this:

# n=438 scale=43955.7 x_range=[-0.589757:0.432624] y_range=[-1:0.97761]
# latitude=33.3 longitude=-60 distance=367590

In this example 438 is the number of points in the file, and 43955.7 is the
scale factor that would restore the original object dimensions.  As
mentioned before, x_range and y_range gives the extent of the image along
the x and y axes, and may be used by 2DtoHPGL.  The second line contains
the transformation details, with the viewpoint distance in absolute user
units.

Hints for using GNUPLOT.  For best results you need to adjust the aspect
ratio to 1:1 with the "set size" command.  With my monitor and Trident 8900
card, I found by trial-and-error that "set size 0.82,1" and "set size
0.83,1" worked well for the standard VGA and for the SVGA 1024x768 modes,
respectively.  For the HP DeskJet printer at 150 dpi, "set size 1.09,1" was
best.  See the file "3D" for the GNUPLOT commands that you might need to
use.  Better, edit that file if necessary, and display your 2D list by
entering "GNUPLOT", followed by "LOAD '3D'".  The file "DJ" is an example
for printer output on the DeskJet.  After displaying with 3D, you could
enter "LOAD 'DJ'", and "REPLOT".

An interesting use of 3DVto2D would be for producing stereograms (stereo
pairs or anaglyphs).  Just make two views with latitude zero and slightly
different longitudes.  A difference of 4 to 7 degrees is generally
recommended.  Exactly how to go about it for display/hardcopy/viewing is
left as an exercise for the reader.

Answers to some Frequently Asked Questions:

The computations in 3dv are essentially as in 3DVto2D, but using integer
arithmetic for speed.  The trick is to scale the values appropriately at
the right places by factors high enough to maintain precision, but not as
high as to overflow the 16-bit integers.  Easier said that done, but not
that difficult, really. The precision achieved was better than the 256x192
resolution of my home-made graphics card for the TRS-80 in the original
implementation.  It is somewhat lower than EGA/VGA, though, and you may
notice that sometimes points jump around a bit.  If you want to be elitist,
the 32-bit integers on 386 processors would be more than enough.  And NO!,
I am not releasing the source of 3dv, it is too ugly.

My original source for 3-D transformations was probably

    Ahuja, D.V., and Coons, S.A. "Geometry for construction and
    display".  IBM Systems Journal 7,188-205. 1968.

(showing my age again!).  This is pretty good and still interesting,
especially the use and explanation of homogeneous coordinates.  Nowadays
you can probably find these things in most Computer Graphics textbooks.
Here goes a list, together with a somewhat concise (!) explanation, from
the "Frequently Asked Questions" file in the Internet/USENET comp.graphics
Newsgroup:

   1) General references for graphics questions:

    Computer Graphics: Principles and Practice (2nd Ed.), J.D. Foley,
      A. van Dam, S.K. Feiner, J.F. Hughes, Addison-Wesley 1990, ISBN
      0-201-12110-7
    Principles of Interactive Computer Graphics (2nd Ed.), Newman and
      Sproull, McGraw Hill, ISBN 0-07-046338-7
    Procedural Elements for Computer Graphics, David F. Rogers, McGraw
      Hill, ISBN 0-07-053534-5
    Mathematical Elements for Computer Graphics 2nd Ed., David F. Rogers
      and J. Alan Adams, McGraw Hill, ISBN 0-07-053530-2
    Applied Concepts in Microcomputer Graphics, Bruce Artwick, Prentice-Hall,
      ISBN 0-13-039322-3
    Digital Picture Processing, vols. 1&2, Azriel Rosenfeld and Avi Kak,
      Academic Press 1976
    Three Dimensional Computer Graphics, Alan Watt, Addison-Wesley, ISBN
      0-201-15442-0
    An Introduction to Ray Tracing, Andrew Glassner (ed.), Academic Press
      1989, ISBN 0-12-286160-4
    Graphics Gems, Andrew Glassner (ed.), Academic Press 1990, ISBN
      0-12-286165-5
    Graphics Gems II, James Arvo (ed.), Academic Press 1991, ISBN
      0-12-64480-0

   2) Drawing three-dimensional objects on a two-dimensional screen.  The
   simple answer is, you divide by the depth.  For a more verbose
   explanation, see any of the above references.

Well... that's all I know!


                  2DtoHPGL

Syntax:  2DtoHPGL [/s] [/xn] [/yn] [/wn] [/hn] [/pn] [infile [outfile]]

Converts a 2D list to HPGL (Hewlett Packard Graphics Language) plotter
instructions.  HPGL (alias IBM-GL, RD-GL, etc.) is used by many plotters,
and is emulated on printers such as our IBM 4029 laser.  The PCL5 language
used by the latest HP printers includes HPGL as a subset.  There are also
software HPGL emulators for other devices, discussed below.

If the /s option is not specified, x_range and y_range information is
expected in the file and used to scale the drawing up to the limits of the
plotting area (with the HPGL IP and SC instructions).  If /s is given, it
is assumed that the data fits into a square bounded by -1 and +1 (see
3DVto2D, above), and the scaling fits this square to the plotting area
(useful for making stereograms, for example).  In both cases the
aspect-ratio is preserved.

The /x and /y options can be used to specify the x and y coordinates of the
centre of the plotting area, in plotter units.  On most (all?) plotters a
plotter unit is 25 microns (40 units/mm).  The default /x5450 and /y3825
corresponds to the centre of an A4 sheet (ISO standard, used in civilized
countries).  For centring on US size A (letter) paper use /x5150.  The
maximum size of the plotting area can be given with /w (width) and /h
(height).  The defaults /w10000 and /h7200 will normally use most of the
available space with both types of paper. More specifically, on the HP
small plotters x goes from 0 to 10300 with size A paper, and to 10900 with
A4, while y goes from 0 to 7650 with both.

A string of up to 15 digits can be given with the /p option to change the
mapping from colour indices to pen numbers.  The default is
/p123456781234567.

Only very basic HPGL instructions are used: DF (defaults), IP (input
scaling points), SC (scale), SP (select pen), PU (move with pen up), and PD
(draw with pen down).  Therefore, compatibility problems should be unlikely
(really!).

Apart from plotters and laser printers, there is a number of HPGL
emulators.  PRINTGL (shareware, US$40, <MSDOS.PLOT>PRTGL118.ZIP in
SIMTEL20) is excellent, working with all sort of graphic cards and printers
(it can also produce PCX raster files).  See DJPLOT.BAT for an example of
coaxing the PaintJet driver in PRINTGL to print on the DeskJet 500C colour
printer (with A4 paper).  Yes, I know, it looks horribly complicated; don't
worry, PRINTGL has also an easy-to-use menu driven front end.  A similar
program is SPLOT ("nagware", US$70, <MSDOS.GRAPHICS>SPLT244.ZIP), which can
also convert to AutoCAD DXF format.  HPGL2PS (<MSDOS.POSTSCRIPT>HPGL2PS.ZIP)
produces output for Postscript printers, is free, and includes C source.
Also free and with source included is <MSDOS.AUTOCAD>HPGL2SCR.ZIP, a
program to convert HPGL to AutoCAD DXF.

Two free HPGL pre-viewers (screen output only), including source code, are
found in SIMTEL in <MSDOS.GRAPHICS>SHOWGL15.ZIP (written in C), and
<MSDOS.GRAPHICS>HPGLVU10.ZIP (Pascal).  Unfortunately, no free HPGL to
(non-Postscript) printer output seems to be available.  It would not be too
difficult, though, to modify the SHOWGL, HPGLVU, or HPGL2PS code, perhaps
using the BGI printer drivers in <MSDOS.BORLAND>PRBGI094.ZIP (Hint! Hint!).
Another alternative would be to use HPGL2PS together with the Ghostscript
Postscript emulator (available in the SIMTEL <MSDOS.POSTSCRIPT> directory).


                  2DtoEXF

Syntax:  2DtoEXF [infile [outfile]]

EasyCAD is a neat little CAD program, produced by Evolution Computing, that
used to come bundled with the MicroSoft mouse.  BTW, I believe in "small is
beautiful", and dislike monsters such as AutoCAD, Mathematica (use DERIVE
instead!), and MS Windows.  Anyway, EasyCAD has a CONVERT utility that can
convert EasyCAD's binary .DWG files to and from ASCII .EXF (Exchange File
Format) files (and also to and from AutoCAD .DXF files).  2DtoEXF converts
2D lists into .EXF files.  I believe that Evolution computing also makes
another system called FastCAD, that presumably also accepts EXF.

2DtoEXF does not use any of the information (x_range, etc) in the initial
comment lines of the 2D file.  After converting to .DWG, you can use
EasyCAD for editing (e.g. adding text, erasing hidden lines, etc.), and/or
plotting/printing.  See the description of 2DtoHPGL above for conversion to
AutoCAD or other systems accepting DXF.


                 LEGAL TRIVIA, ETC.
                 ------------------

You can do whatever you like with all this (just like that!).  I thought
hard about placing copyright notices everywhere, having read horror stories
about people stealing public domain software and restricting its use by
others.  Finally decided against it, for no good reason, really.  I just
did not feel like adding to what is hopefully no more than generalized
paranoia.  If I am wrong, the world will just have to learn to survive
without these earth-shattering pieces of software.  Anyway, if you get rich
with this without giving me my part of the booty I wish you burn in Hell,
your yacht sinks, and the IRS investigates you.

I also gather that, because of a lawyers infestation somewhere, I am
supposed to say things like that I am completely irresponsible (a well
known fact), that this software is not guaranteed to improve your sex life
(or your money back), that IBM is a registered trademark of IBM, etc.
Whatever.  Lawyers: I am a fair distance away, and I have no money (er...
umm... don't take it as a challenge, guys!).

After writing this, Keith Petersen asked me that if I include here the
SIMTEL.DOC file "Please make it clear that SIMTEL20 has no connection with
your product and does not endorse it" (see what I mean?).  SIMTEL20 HAS NO
CONNECTION WITH MY PRODUCT, AND DOES NOT ENDORSE IT  :-) .

By the way, my employer had nothing to do with this either.  Here goes my
home address until August 1992 or so.  I am moving but I don't know where
yet.  My e-mail address will probably change sooner than that, and I may
temporarily lose Internet access at any moment.

Oscar García
1 Clyde Street
Rotorua
New Zealand              Internet: [e-mail]