Gnuplot: How to get "time-friendly" hour/min x-axis tick layout

Question

I'm having trouble getting a "time friendly" X-axis layout in Gnuplot.

I need to present some data referring to a period within one day; the time X data is represented in decimal form, e.g. X=20.75 meaning 20 hours and 45 mins, the range is generally [0 : 24], but normally a subset, such as [2.25 : 8.75].

The default Gnuplot x-axis layout will be something like the range [0 : 25] with major tics at 0,5,10,15,..., which is nice for normal decimal data, but I would like it to choose something more "time friendly" in the usual clock manner, I mean major ticks at hours 1,2,3 or 6 and minor ticks at 1,5,15 or 30 minutes, suitably chosen depending on the range.

Does anybody know how to do that?

Solution 1

How about this?

set xtics 1, 0.25

Unfortunately, according to the manual:

Minor tics can be used only with uniformly spaced major tics. Since major tics can be placed arbitrarily by set {x|x2|y|y2|z}tics, minor tics cannot be used if major tics are explicitly set.

Solution 2

Using gnuplot 4.6 patchlevel 0
I ended up with this shell script that can be called followed by the desired output name:

save this as makeChart.sh

path='/home/you/yourdir/dat2.txt'

echo "
set terminal unknown
plot '$path' u 1:2
min = (GPVAL_Y_MIN-1)
max = (GPVAL_Y_MAX+1)

set terminal pngcairo size 1400,600 enhanced font 'Helvetica,12'
set timefmt '%H:%M'
set ylabel 'Temperature'
set xlabel 'Time'
unset key
set grid
set title 'Temperature Sensor 1'
set xtics rotate right
set xtics 0,1800,96000
set xdata time
set mxtics 2
set format x '%H:%M'
set format y '%.2f'

set yrange [min:max]

set output '/var/www/somefolder/$1'
plot '$path' u 1:2 index 0  with lines" | gnuplot

Some sample data from dat2.txt:
A temperature reading every 5 minutes over one day.

00:05   74.75
00:10   74.85
00:15   74.85
.
.
.
23:30   75.65
23:35   75.65
23:40   75.52
23:45   75.65
23:50   75.65
23:55   75.75

run it like this:
you@yourpc $sudo ./makeChart.sh chartx.png

Kept playing with the xtics range until I had 30 minute intervals.