You can comprehend the data from the Cascade TextLogger more easily by plotting it. Since there is no widget available in GTK that can plot real-time trends for 3 values, we have used gnuplot, a Linux plotting program. But gnuplot was designed primarily for making static plots, so we've had to push it a little to do what we want.

To get two different plots (Recent and All), we use three configuration files and a data file. The plmain.cfg configuration file holds commands that are common to both plots, like labels, borders, and data styles. The plrecent.cfg and plall.cfg files each have different commands to make their unique plots. They each load the plmain.cfg file and the continuously-updated data file (/tmp/cogentdemo/pllogtimes.dat explained below), and then apply their own commands.

pllogtimes.dat

To simulate a scrolliing trend graph, we put gnuplot into a loop and feed it new values every second. We control the x-axis (the time axis), with this three-line file that is updated by the prepare_times function every 1/10 second. Here is a typical example of the contents of pllogtimes.dat, written on Thursday, Feb 28, 2002, at 5:00 p.m. and 7 seconds (or 1014933607.7161740064620972 seconds in system time):

cuttime = 1014930000
top = 3607.7161740064620972
bottom = 3592.7161740064620972

The cuttime variable is the current time in seconds, minus the last 4 digits. The plot commands in plrecent.cfg and plall.cfg subtract this number from the log time values to reduce them to 4-digit numbers. If we don't do this, the time values will be very high, causing gnuplot to display the x-axis labels in scientific notation, obscuring the number of seconds.

The top variable is simply the present time minus the cuttime. This value is used to specify the top of the range for plrecent.cfg. The bottom variable is 15 seconds less than the top, used for the bottom of the range in plrecent.cfg. The range for plall.cfg is the default—all the data.

plmain.cfg

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#DOCUMENT:      plmain.cfg
#DEPENDENCIES:  none
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# Set up labels and borders.

set xlabel "Time" 0,0
set ylabel "Value" 1,0
set border
set tics out
set grid xtics ytics
set nokey

# Set up line width and coloring.  We use the "set linestyle"
# command to get a number for each line, which then gives us
# access to the colors we need, in the order we need them.

set data style lines

set style line 1 lw 1 #red
set style line 2 lw 1 #green
set style line 3 lw 1 #blue
set style line 4 lw 1 #magenta (purple)
set style line 5 lw 1 #light blue
set style line 6 lw 1 #dark brown
set style line 7 lw 1 #orange
set style line 12 lw 1 #magenta
set style line 18 lw 1 #light green
set style line 19 lw 1 #dark blue


# Set up the terminal to X Windows. 

set terminal x11

# Then set the y-axis to the range of MV (0 - 200).

set yrange [0:200]

plrecent.cfg

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#DOCUMENT:      plrecent.cfg
#DEPENDENCIES:  plmain.cfg
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

set title "Cascade TextLogger Output - Recent"

load "plmain.cfg"

# Load the file that holds the present time data (within 1/10
# second) used for setting labels, as well as the most recent
# and 15-seconds-ago times used for making the Recent plot.

load "/tmp/cogentdemo/pllogtimes.dat"

set xrange [bottom:top]

# Make the plot.  The cuttime value comes from pllogtimes.dat.  It is used
# to cut the top digits off the system time, reducing it to a four-digit
# number, which displays well.  Pause for 1 second, then plot the latest
# values from the tlrecent.dat and tlold.dat files.  Continue until
# gnuplot is terminated.

plot '/tmp/cogentdemo/tlrecent.dat' using (column(1) - cuttime):2 title 'SP' ls 3, \
     '/tmp/cogentdemo/tlrecent.dat' using (column(1) - cuttime):3 title 'MV' ls 2, \
     '/tmp/cogentdemo/tlrecent.dat' using (column(1) - cuttime):4 title 'PV' ls 1, \
     '/tmp/cogentdemo/tlold.dat' using (column(1) - cuttime):2 title 'SP' ls 3, \
     '/tmp/cogentdemo/tlold.dat' using (column(1) - cuttime):3 title 'MV' ls 2, \
     '/tmp/cogentdemo/tlold.dat' using (column(1) - cuttime):4 title 'PV' ls 1

pause 1
load "/tmp/cogentdemo/pllogtimes.dat"
reread

plall.cfg

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#DOCUMENT:      plall.cfg
#DEPENDENCIES:  plmain.cfg
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

set title "Cascade TextLogger Output - All"

load "plmain.cfg"

# Load the file that holds the present time data (within 1/10
# second) used for setting labels, as well as the most recent
# and 15-seconds-ago times used for making the Recent plot.

load "/tmp/cogentdemo/pllogtimes.dat"

# Make the plot.  The cuttime value comes from pllogtimes.dat.  It is used
# to cut the top digits off the system time, reducing it to a four-digit
# number, which displays well.  Pause for 1 second, then plot the 
# tloutput.dat file with the latest data. Continue until gnuplot is
# terminated.

plot '/tmp/cogentdemo/tloutput.dat' using (column(1) - cuttime):2 title 'SP' ls 3, \
     '/tmp/cogentdemo/tloutput.dat' using (column(1) - cuttime):3 title 'MV' ls 2, \
    '/tmp/cogentdemo/tloutput.dat' using (column(1) - cuttime):4 title 'PV' ls 1

pause 1
reread