#! /usr/bin/env perl
# $Id: lines.pl 743 2006-12-18 23:10:02Z jnieuwen $

use strict ;
use warnings ;

use GD::Graph::lines ;

# Get the commandline parameters ;
my $infile = shift @ARGV ;
my $outfile = shift @ARGV ;

# Init variables.
my @xval = () ;
my @yval = () ;
my @zval = () ;
my $ymax = 0 ;
my $xcount  = 0 ;
my $sum=0 ;
my $count=0 ;
my @cache = () ;

open (FILE,"$infile") or die "Could not open $infile\n" ;
while (my $line = <FILE>) {
	next unless ($line =~ /O=RMC/) ; # Skip no fix lines.
	chomp $line ;
	my ($info,$time,undef,$lat,$lon,undef,undef,undef,$head,$speed,undef,undef) = split(/ /,$line) ;
	next if ($speed < 1) ; # Filter out standing still moments.
	push @cache, $speed ;
	if ($#cache > 59) {
		shift @cache ;
		my $y = 0 ;
		for (my $i=0; $i <= $#cache; $i++) {
			$y += $cache[$i] ;
		}
		$y = ($y / ($#cache+1)) * 3.6 ; # Convert to km/h and average over cache length.
		$sum += $y ;
		push (@yval,$y) ;
		push (@zval,$sum/++$count) ;
		$ymax = $y if ($y > $ymax) ;
	}
}
close FILE ;

# Set the x values.
undef @xval ;
foreach my $i (@yval) {
	push(@xval,$xcount++/60) ;
}

my @data = ([@xval],[@yval],[@zval]) ;

my $graph = GD::Graph::lines->new(1000,400) ;
$graph->set(
	x_label			=> 'time in minutes',
	long_ticks		=> 1, 
	y_label			=> 'km/h',
	y_min_value		=> 0,
	y_max_value		=> 50,
	y_tick_number	=> 10,
	y_label_skip	=> 1,
	x_label_skip	=> 300
) or die $graph->error;

my $gd = $graph->plot(\@data) or die $graph->error;
open(IMG, ">$outfile") or die $!;
binmode IMG;
print IMG $gd->png;
close IMG ;