5/2002:
Ygl emulates SGI's GL routines under X11. It compiles fine under AIX 3.2,
HP-UX 7.0/8.0/9.0, Linux with XFree, SunOS,
ConvexOS and others, but needs an ANSI-C compiler (gcc is ok).
 
http://www.thp.uni-duisburg.de/Ygl/ReadMe.html
 
 -> a way to use sg3d under Linux (should be better than NVIZ and
    easier to maintain)
 
-------------------------------------------


	THIS VERSION NOT RELEASED WITH ANY VERSION OF GRASS

	Read the INSTALL file for installation instructions.

###################### CHANGELOG - SG3d4.2   ############################

March 1996

Fixed all code to read maps as floating point with possible NULL.  NULLs
in elevation map leave holes in surface.  NULLs in color maps just 
use the GRASS color used to represent NULL.  (When using 3 color maps
for R, G, B, in range 0-255, NULLs are translated to zero)

Major changes to sites panel to read new sites format with multiple
attributes and allow mapping of various attributes to site marker
size, shape, color, etc.  Each attribute may be transformed by entering
an additive translation value and a scaling value.  Also added "Info" 
button to display information about the current sites list.

Added various ways to label site markers on Label panel.  The "field"
boxes refer to the Nth such field in the site attribute order, e.g.:
-88.205154|40.108536|#77005 @IL @Urbana %36344 %14006 %1.795031
    string field #2 is "Urbana" 
    value field #3 is 1.795031
If the sites file contains descriptions of the fields, you can use the
"Info" button on the sites panel to find the field you're looking for.
Ranges and comma separated fields are also valid: 1-3
						  2,4
e.g., Using the above site, specifying 2,1 as string fields on the
label panel would label the site "Urbana IL".
For value fields, you can also use letters to represent dimensions:
[nNsS] for northing or [eEwW] for easting or [zZ] for 3rd spatial
dimension, if present.

"piechart" draws a piechart label for each site using the value fields
you specify to represent slices.  These fields should be in the range
0.0 - 1.0, as a portion of the whole pie.  Unless "grey scale" is 
selected, colors used for the slices are the colors on the color bar 
at top, in reverse (right - left) order.  Since you can set the rightmost 
five colors, you have some control over pie slice colors.  (If you want
more colors that you can set, change NUM_CUSTOM_COLORS in externs.h and
recompile the whole thing).  Unfilled pie portions remain white; if sums
of specified fields are > 1.0 then the pie just keeps on drawing over
the beginning slices, and a warning is printed.  Piechart size is 
controlled by the size controls on the sites panel, but because the
piecharts are not drawn ON the surface in 3D, the size units are not
comparable to drawing actual site markers where size is in map units
(that's why piechart is a label rather than a site marker).


###################### CHANGELOG - SG3d4.1.4 ############################

Fixed bug with drawing round tree & glyph site objects caused when I
switched to using the sphere library.


###################### CHANGELOG - SG3d4.1.3 ############################

1.  Pulldown menus replace menu panel.  Also added CLOSE button to all
pop-up panels.  Some functions under the "File..." pulldown are
duplicated (Img Dump, Quit, new vect on vector panel, etc), but are
included in the pulldown for completeness.

2.  Screendoor transparency replaced by alpha blending on machines that
support it (otherwise still uses screendoor).  Alpha blending simply
blends the thing that's drawing with whatever is currently on the
screen at a specified blending level.  For it to work properly, 
every polygon which is drawn would first have to be depth-sorted,
then drawn in order from back to front.  This is not implemented, but
you can achieve good results by viewing from the south or southeast 
corner, so the surface draws toward you.  If drawing multiple surfaces,
load the lowest one first (viewing from above).  If drawing 3d sites below
a surface, select "no clear on redraw" from options, then clear, draw
sites, set surface transparency, draw surface.  Transparency
settings also affect drawing of solid site objects.

3.  Custom colors now available on color bars.  To change any of the 
three custom colors on the bar, select "set" from next to any color bar.

4.  Added "plan view" button for positioning directly over the data 
automatically.  This also automatically puts you in ortho mode to
eliminate perspective distortions. 

5.  Added labeling of sites on the "Labels..." panel.  "in box" button puts
the label in a light or dark grey box to contrast with font color.
"values" & "labels" toggle buttons control label text - with both ON,
you get the entire description field for the site; with "values" ON,
you get the first blank-deliminated field of the description; and
with "lables" ON you get the description EXCEPT for the first
blank-deliminated field.  In all cases, any leading '#' characters are
ignored.

6.  Added Legends on the "Labels..." panel.  Too messy to explain how 
they work here, but just play with it & figure it out :-).  Basically,
you just click on "Legend", then use the mouse to drag out a box on
the display where you want the legend.  There are two general types 
of legends - continuous (default) and discrete.  For both types, you
may define a range of values rather than use the whole range in the map,
and for discrete legends, you may even enter a list of exactly which
categories you want to see.  When drawing discrete legends, an attempt is
made to label each category -  when drawing continuous legends, only a few
"nice" numbers and the min & max are labeled. 
The "invert" toggle will make your legend go the wrong :-) way - low on 
top[or right] and high on bottom[or left], the way d.legend does it.  
(Actually this makes some sense for discrete data, but not at all for 
elevation colors - anyway, now you can choose.)

7.  New features (5) & (6) above also use the font info at the top of 
the Label panel for font type/size/color of legend & site labels.
So if you're use to d.legend automatically defining the font size - 
sorry, this won't do that for you (but YOU have more control).  The 
undo button works for undoing labels & legends, but not for site labels.

8.  Clear button added.  Mostly for the case described in #2 above.

9.  Quit button now requires confirmation (GRASS window prompt). There
is a no-fault quit under the file menu if this bothers you.

10.  A little BUG found when running under IRIX 5.2 - the "Surface Only"
toggle, which is suppose to draw the surface with lights but no color
instead draws the surface with color but no lights!  I really don't 
think this is my problem - so I'll wait until the next IRIX comes out
& see if it fixes itself. (Did you hear the one about the three guys
from IBM - a salesman, a hardware designer, & a programmer - who were
driving down the road when they got a flat tire...)
Actually, I could put a kludgey fix in at the loss of some performance,
but for now, if you want "Surface Only", you'll have to load a new
color file which is all white.


###################### CHANGELOG - SG3d4.1.2 ############################

Added "Set Exact..." to movement panel.  It pops up another panel that
has type-in for viewer & look-to position & perspective, as requested by 
Delores Andaluz & Bob Sullivan at Argonne.  Not extensively tested.
Perspective should be accurate to 10ths of degrees.

Remember to hit RETURN after typing in a new value in any of the type-ins.


###################### CHANGELOG - SG3d4.1.1 #########################

Undocumented features in this version:

Three levels of "screen door" transparency:
This is implemented by simply drawing a pattern of pixels rather than
solid pixels for "transparent" objects.  Note that this means that if
a transparent surface is drawn over an object or surface with the same 
tranparency level, the first will totally disappear.  (Or if an object 
or surface is drawn behind another at the same transparency level, it 
too will not be visible.

"No clear on redraw" added to Options panel.  This toggle prevents the
graphics screen from being erased when "Draw" is selected.  

"Where am I" added to Control panel.  This button causes the viewer's
current position, in map units, to be printed to stderr.  If the viewer
is over part of the surface, height to the surface is also given.

Site objects:
A selection of solid objects that can be used as site markers.  These
will also be drawn according to the currently selected transparency
level.  "Glyphs" will use the site category to stretch a sphere into
a cone shape in a positive or negative direction, depending which 
glyph is selected.  Both glyphs may be selected at the same time.  If
the -z option was used at startup (making the site category the Z value),
then the glyph attribute used is a value following the Z attribute in the
sites file.  Glyphs can be used like error bars on a line graph - to
represent error in surface topology, or to represent some other
attribute of the sites.

scolor option:
A raster filename may be given at startup with the option scolor=name,
causing the color rules from that raster file to be applied to the
site category to determine the site drawing color.  If the -z option was
used at startup (making the site category the Z value), then the value
used for color is a value following the Z attribute in the sites file.

In other words, for the previous two new features, the site format would
look like this:

<easting>|<northing>|#<elevation> 
(if using -z)
OR
<easting>|<northing>|#<elevation> <cat>  
(if using -z & (scolor= and/or glyphs))
OR 
<easting>|<northing>|#<cat> OR <easting>|<northing>|<cat>
(if using scolor= and/or glyphs)

<elevation> may be a floating point value, while <cat> may not.

WARNING: This is not an offical GRASS data format!  
It may NOT be supported in the future!

#########################################################################


***************************************************************************
Bill Brown				e-mail: brown@gis.uiuc.edu
Geographic Modeling Systems Laboratory  phone:  (217) 333-5077
220 Davenport Hall - MC 150
607 S. Mathews
Urbana, IL  61801

See the SG3d visualization demo at URL:
http://www.cecer.army.mil/grass/viz/VIZ.html

See current documentation updates at:
http://www2.gis.uiuc.edu:2280/modviz/appdoc/sg3d42.html
***************************************************************************


