Gview reads polygonal lines or a polygonal line drawing from an
ASCII input file (which defaults to standard input), and views it interactively,
with commands to zoom in and out, perform simple editing operations, and
display information about points and polylines. The editing commands can
change the color and thickness of the polylines, delete (or undelete)
some of them, and optionally rotate and move them. It is also possible to
generate an output file that reflects these changes and is in the same format
as the input.
rotate commands are undesirable when just viewing a graph, they are only enabled if
gview is invoked with the
Clicking on a polyline with button 1 displays the coordinates and a
t value that tells how far along the polyline.
(t=0 at the first vertex,
t=1 at the first vertex,
t=1.5 halfway between the second and third vertices, etc.) The
-l option generates a log file that lists all points selected in this manner.
The most important interactive operations are to
zoom in by sweeping out a rectangle, or to
zoom out so that everything currently being displayed shrinks to fit in the swept-out
rectangle. Other options on the button 3 menu are
unzoom which restores the coordinate system to the default state where everything
fits on the screen,
recenter which takes a point and makes it the center of the window, and
square up which makes the horizontal and vertical scale factors equal.
To take a graph of a function where some part is almost linear and
see how it deviates from a straight line, select two points on this
part of the graph (i.e., select one with button 1 and then select the
other) and then use the
slant command on the button 3 menu.
This slants the coordinate system so that the line between the two
selected points appears horizontal (but vertical still means positive
y). Then the
zoom in command can be used to accentuate deviations from horizontal.
There is also an
unslant command that undoes all of this and goes back to an unslanted coordinate
There is a
recolor command on button 3 that lets you select a color and change everything
to have that color, and a similar command on button 2 that only affects
the selected polyline. The
thin command on button 2 changes the thickness of the selected polyline
and there is also an undo command for such edits.
Finally, button 3 had commands to
read a new input file and display it on top of everything else,
restack the drawing order (in case lines of different color are drawn on top of
write everything into an output file, or
exit the program.
Each polyline in an input or output file is a space-delimited
y coordinate pair on a line by itself, and the polyline is a sequence
of such vertices followed by a label. The label could be just a
blank line or it could be a string in double
quotes, or virtually any text that does not contain spaces and is
on a line by itself. The label at the end of the last polyline is
optional. It is not legal to have two consecutive labels, since that
would denote a zero-vertex polyline and each polyline must have at least
one vertex. (One-vertex polylines are useful for scatter plots.)
If the label after a polyline can contains the word
Thick or a color name
White), whichever color name comes first will be used to color the polyline.