Improved spacing of tics.

TimeSeries.pm

@@ -6,7 +6,7 @@ use Data::Dumper;
 use HTTP::Date qw(parse_date);
 use Time::Local qw(timegm_nocheck);
 
-$VERSION = do { my @r=(q$Revision: 1.5 $=~/\d+/g);sprintf "%d."."%02d"x$#r,@r};
+$VERSION = do { my @r=(q$Revision: 1.6 $=~/\d+/g);sprintf "%d."."%02d"x$#r,@r};
 
 sub new {
     my ($class, %opts) = @_;
@@ -87,14 +87,30 @@ sub output_format {
 
 
 
+=head2 dstcorr $time [, $period]
+
+corrects for time shifts caused by DST switches by aligning the
+time to the given period in local time.
+
+Example:
+
+1048989600 is 2003-03-30 00:00:00 CET. 4 hours (14400
+seconds) later, the time is 2003-03-30 05:00:00 CEST. To get back to a
+4 hour period starting at midnight, 1 hour needs to be subtracted, so 
+C<dstcorr(1048993200, 14400)> returns 1048989600, which is 2003-03-30
+04:00:00 CEST.
+
+=cut
+
 sub dstcorr {
-    my ($time) = @_;
+    my ($time, $period) = @_;
+    $period = 24 * 3600 unless ($period);
 
     ($sec,$min,$hour,$mday,$mon,$year) = localtime($time);
-    my $toff = $hour * 3600 + $min * 60 * $sec;
+    my $toff = ($hour * 3600 + $min * 60 * $sec) % $period;
     if ($toff != 0) {
-	if ($toff > 12*3600) {
+	if ($toff > $period/2) {
-	    $toff -= 24 * 3600;
+	    $toff -= $period;
 	}
 	print STDERR "correcting time by $toff seconds ";
 	printf STDERR "from %04d-%02d-%02d %02d:%02d:%02d ", $year+1900, $mon+1, $mday, $hour, $min, $sec;
@@ -137,10 +153,19 @@ sub plot {
 
     # compute ticks
 
+    # The spacing of the ticks a bit tricky: They should be related to
+    # common time units (1 hour, 1 day, 1 week, ...), which are
+    # irregular and not even of constant length (a day can be 23, 24 or
+    # 25 hours, a month 28 to 31 days, a year 365 or 366 days). Also the
+    # spacing shouldn't be too tight or too sparse. So there's quite a
+    # bit of special-case code below (but also much code duplication
+    # which should be cleaned up).
+
     my $firsttime = $self->{data}[0][0];
     my $lasttime = $self->{data}[$#{$self->{data}}][0];
 
     if ($lasttime - $firsttime > 3 * 365 * 24 * 3600) {
+	# more than 3 years: 1 tick/year
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
 	$sec = $min = $hour = 0;
 	$mday = 1;
@@ -166,6 +191,8 @@ sub plot {
 	$lasttime = $time;
 	print $ctlfh ")\n";
     } elsif ($lasttime - $firsttime > 3 * 30 * 24 * 3600) {
+	# 3 to 36 months: 1 tick/month
+
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
 	$sec = $min = $hour = 0;
 	$mday = 1;
@@ -189,6 +216,8 @@ sub plot {
 	$lasttime = $time;
 	print $ctlfh ")\n";
     } elsif ($lasttime - $firsttime > 30 * 24 * 3600) {
+	# 30 ... 90 days: 1 tick/week.
+
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
 	$firsttime -= 86400 * $wday;
 
@@ -212,7 +241,9 @@ sub plot {
 	}
 	$lasttime = $time;
 	print $ctlfh ")\n";
-    } elsif ($lasttime - $firsttime > 3 * 24 * 3600) {
+    } elsif ($lasttime - $firsttime > 10 * 24 * 3600) {
+	# 10 .. 30 days: 1 tick per day.
+
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
 	$sec = $min = $hour = 0;
 	my $time = $firsttime = timelocal($sec,$min,$hour,$mday,$mon,$year);
@@ -233,7 +264,32 @@ sub plot {
 	}
 	$lasttime = $time;
 	print $ctlfh ")\n";
+    } elsif ($lasttime - $firsttime > 2 * 24 * 3600) {
+	# 2 .. 10 days: 1 tick/4 hours
+
+	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
+	$sec = $min = $hour = 0;
+	my $time = $firsttime = timelocal($sec,$min,$hour,$mday,$mon,$year);
+	print $ctlfh "set xtics rotate (";
+	my $comma = 0;
+	for (;;) {
+	    ($sec,$min,$hour,$mday,$mon,$year) = localtime($time);
+	    if ($comma) {
+		print $ctlfh ", ";
 	    } else {
+		$comma = 1;
+	    }
+	    printf $ctlfh qq|"%04d-%02d-%02d %02d:%02d" %d|, $year+1900, $mon+1, $mday, $hour, $min, $time;
+	    if ($time > $lasttime) {last}
+
+	    $time += 4 * 3600;
+	    $time = dstcorr($time, 4 * 3600);
+	}
+	$lasttime = $time;
+	print $ctlfh ")\n";
+    } else {
+	# less than 2 days: 1 tick per hour.
+
 	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($firsttime);
 	$sec = $min = 0;
 	my $time = $firsttime = timelocal($sec,$min,$hour,$mday,$mon,$year);