Unstuck in Time and Space: An Investigation into Location over WiFi.

I track my location with Google and my phone, because I lack sufficient paranoia. To the right is my June 30.

I swear that I didn't leave the Greater Lafayette area. I certainly didn't teleport to the southern suburbs of Indianapolis.

This happens to me all the time, and it has bugged me a lot. But, normally I've just looked and griped, rather than trying to work it out.

Today, however, I'm watching a compiler or two, so I have some time I can use to work this out.

The protocol is KML, and this is what it looks like:

	<?xml version="1.0" encoding="UTF-8"?>
	<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
	<Document>
	<name>Location history from 06/30/2015 to 07/01/2015</name>
	<open>1</open>
	<description/>
	<StyleMap id="multiTrack">
	<Pair>
	<key>normal</key>
	<styleUrl>#multiTrack_n</styleUrl>
	</Pair>
	<Pair>
	<key>highlight</key>
	<styleUrl>#multiTrack_h</styleUrl>
	</Pair>
	</StyleMap>
	<Style id="multiTrack_n">
	<IconStyle>
	<Icon>
	<href>http://earth.google.com/images/kml-icons/track-directional/track-0.png</href>
	</Icon>
	</IconStyle>
	<LineStyle>
	<color>99ffac59</color>
	<width>6</width>
	</LineStyle>
	</Style>
	<Style id="multiTrack_h">
	<IconStyle>
	<scale>1.2</scale>
	<Icon>
	<href>http://earth.google.com/images/kml-icons/track-directional/track-0.png</href>
	</Icon>
	</IconStyle>
	<LineStyle>
	<color>99ffac59</color>
	<width>8</width>
	</LineStyle>
	</Style>
	<Placemark>
	<name>Latitude User</name>
	<description>Location history for Latitude User from 06/30/2015 to 07/01/2015</description>
	<styleUrl>#multiTrack</styleUrl>
	<gx:Track>
	<altitudeMode>clampToGround</altitudeMode>
	<when>2015-06-30T13:11:50.556-07:00</when>
	<gx:coord>-86.9113936 40.4224106 0</gx:coord>
	<when>2015-06-30T13:13:05.103-07:00</when>
	<gx:coord>-86.1233968 39.6461108 0</gx:coord>
	</gx:Track>
	</Placemark>
	</Document>
	</kml>

view raw history-06-29-2015.kml hosted with ❤ by GitHub

That isn't all day's results, merely the point in time I jumped 67 miles to the southeast. I was going to try to use a KML-specific Perl module, but found that the ones I could find were more about generating it than parsing it, and it's XML, so I figured what the heck.

I had previous code to work out the distance between two points, so it was an easy case of parsing to find the jump:

	#!/usr/bin/env perl
	use feature qw{ say } ;
	use strict ;
	use warnings ;
	use utf8 ;
	use DateTime ;
	use Math::Trig qw(deg2rad pi great_circle_distance asin acos) ;
	# Lafayette: 40°25′2″N 86°52′43″W
	# Greenwood: 39°36′41″N 86°07′05″W
	my $file = '/home/jacoby/Dropbox/history-06-29-2015.kml' ;
	my @when ;
	my @latlong ;
	if ( open my $fh, '<', $file ) {
	while (<$fh>) {
	if (m{<when>}) {
	my ($time) = m{<when>(.+)</when>} ;
	push @when, $time ;
	}
	if (m{<gx:coord>}) {
	my ($place) = m{<gx:coord>(.+)</gx:coord>} ;
	push @latlong, $place ;
	}
	}
	close $fh ;
	}
	my $last_time ;
	my $last_place ;
	for my $i ( map { $_ - 1 } 1 .. scalar @when ) {
	my $time = $when[$i] ;
	my $place = $latlong[$i] ;
	if ($last_time) {
	my $tt = ( split m{\.}, $time )[0] ;
	my ( $long, $lat ) = split m{\s+}, $place ;
	my $d_time = diff_time( $time, $last_time ) ;
	my $d_place = diff_loc( $place, $last_place ) ;
	my $flag = ( $d_place > 1 ) ? '*' : ' ' ;
	say join "\t", $flag, $tt, $lat, $long, $d_time,
	( sprintf '%.5f', $d_place
	if $d_place > 30 ;
	}
	$last_time = $time ;
	$last_place = $place ;
	}
	sub diff_loc {
	my ( $place1, $place2 ) = @_ ;
	my ( $lon1, $lat1 ) = split m{\s+}, $place1 ;
	my ( $lon2, $lat2 ) = split m{\s+}, $place2 ;
	return haversine( $lat1, $lon1, $lat2, $lon2 ) ;
	}
	sub haversine {
	my ( $lat1, $lon1, $lat2, $lon2 ) = @_ ;
	my $r = 3956 ;
	my $dlon = deg2rad($lon1) - deg2rad($lon2) ;
	my $dlat = deg2rad($lat1) - deg2rad($lat2) ;
	my $a
	= sin( $dlat / 2 )**2
	+ cos( deg2rad($lat1) ) * cos( deg2rad($lat2) ) * sin( $dlon / 2 )
	**2 ;
	my $c = 2 * ( asin( sqrt($a) ) ) ;
	my $dist = $r * $c ;
	return $dist ;
	}
	sub diff_time {
	my ( $time1, $time2 ) = @_ ;
	my $t1 = parsetime($time1) ;
	my $t2 = parsetime($time2) ;
	my $diff = abs $t2->epoch - $t1->epoch ;
	return $diff ;
	}
	sub parsetime {
	my $string = shift ;
	$string =~ s{\..+$}{} ;
	my @time = split m{\D+}, $string ;
	my $dt = DateTime->new(
	year => $time[0],
	month => $time[1],
	day => $time[2],
	hour => $time[3],
	minute => $time[4],
	second => $time[5],
	time_zone => 'America/Indiana/Indianapolis'
	) ;
	return $dt ;
	}

view raw find_greenwood.pl hosted with ❤ by GitHub

Breaking it down, at 2015-06-30T13:13:05.103-07:00 I go 67 miles to Greenwood, and at 2015-06-30T13:53:31.467-07:00 I pop back.

Let me bring up an other map.

 I didn't have any mapping software going, and I was using wifi, so this data is location via wifi not GPS. I know, though, that the group that runs my servers has a weekly "coffee break" on Tuesdays, that I met with my admin there, and I walked around toward his office before goign back to mine. His building is off S. Grant St., and I walked next to Hawkins Hall, in front of Pao Hall, near the Forestry Building and down to my office in Whistler.

So, question is, how does location over WiFi work? I recall hearing that routers and access points report location, but I'm not sure of the protocols involved. I can imagine two possible scenarios that cause this.

First is that one of Purdue's routers is misreporting location, either in Forestry or Pao. This is possible; I have another issue that I haven't worked through yet where I leap instantly to the EE building, and it seems that's entirely based on location within my building.

The second scenario, one I'm taking more and more seriously, is that there's a replicated MAC address or something between the apartments across from Pao Hall. I say "or something" because MAC addresses should be unique. The thing that makes me suspect this is that it points me to a residential neighborhood south of Indy, and I could see that mistake happening with two residential routers or two experimental electronics projects.

I'm curious about how to test this, because I do want to know it has something to do with Purdue's networking gear before I complain. I'm also curious about how these things actually work. I could very much see me walking around, looking at Google Maps and tripping over things, then trying to dump my ARP tables or something.