#!/usr/bin/perl

# Convert Lat Long Alt to Earth-Centered Earth-Fixed
# Lat/Long in dd.dd or dd:mm[:ss.ff]
# Alt in meters
# 
# Constants from <http://mathforum.org/library/drmath/view/51832.html>
# Geodetic Datums Overview 
#    <http://www.colorado.edu/geography/gcraft/notes/datum/datum_f.html>
# 
# $Id: LLA2ECEF,v 1.3 2005/05/04 13:21:19 eric Exp $

use strict;

my $PI = 3.141592648;
my $a = 6378137; # meters
my $f = 1/298.257224;

my $lat = &radians($ARGV[0]);
my $lon = &radians($ARGV[1]);
my $h = $ARGV[2];
my $C = 1 / (sqrt( cos($lat)**2 + (1-$f)**2 * sin($lat)**2 ));
my $X = ($a*$C + $h) * cos($lat) * cos($lon);
my $Y = ($a*$C + $h) * cos($lat) * sin($lon);
my $Z = ($a*$C + $h) * sin($lat);
print "X:$X, Y:$Y, Z:$Z\n";

sub radians {
    my ($degrees) = @_;
    if ($degrees =~ m/^
	\-?
	(?:
	 (?:\d+ (?: \. \d*)?) || 
	 (?:\. \d+)
	 )$/x) {
    } elsif ($degrees =~ m/^
	     (\-)?
	     (\d*):	# degrees
	     (\d*)	# minutes
	     (?: :([\d\.]*) )?	# optional seconds
	     $/x) {
	$degrees = (defined $1 ? -1 : 1) * ($2 + $3/60 + $4/3600);
    } else {
	die "Can't parse \"$degrees\" as degrees\n"
    }
    return $degrees * $PI / 180;
}