GPS Apps for Smart Phone and PC YHA … Apps for Phone and...YHA Bushwalking Club Night Presentation...

GPS Apps for Smart Phone and PC YHA Bushwalking Club Night Presentation

Lutz Lademann

walks@lademann.de

May 2016

Content

• How Does GPS Work• What are GPX Files• Where to Find GPX Files/Tracks/Walks• How to View/Modify/Create Tracks

– Online– PC

• The Problem With the Elevation – DEM• GPS Smartphone Apps

– Turn-by-turn Navigation– Compass– Location Sharing– Navigation

GPS – How Does it Work?

GPS - Global Positioning System

• How does GPS work?

• What does “assisted GPS” work?

• How accurate is GSP?

• What’s the difference to handheld dedicated navigation systems?

How Does GPS Work?• 31 US GSP satellites in orbit

over earth

• Each transmits signal containing– ID

– Time/Date

– Position of satellite

• GPS receiver “triangulates” multiple satellite signals to determine position

• Since 2011, there are additional 24 Russian GLONASS satellites

• Modern GPS receivers support both systems

Assisted GSP

• Initial Time to First Fix (TTFF) can take 30s and more if only GPS data is used

• Assisted GSP uses location information from Cell Phone Base Stations or WiFi hotspots to roughly determine the position of the cell phone

• This allows quicker TTFF for the GPS receiver

• Works only in regions with cell phone coverage

Does GPS work without cell phone reception?

How Accurate is GPS?

• It depends: Best case is between 3m and 100m• 3m if GPS receiver supports WAAS and WAAS is available (only

North America), smart phone typically do not support WAAS , the wide area augmentation system (additional radio signal).

• 5-15m without WAAS, depending on number of satellites visible

• 100m with Selective Availability switched on

Accuracy, cont’d

• GPS has weak signal

• Needs open sky – does not work in closed rooms!

• Forest Canopy can have big impact

• Dense / wet clouds

• Reflection / Multipath problem

Coordinate Notations

• Degrees: DD.dddddd°

• Degrees, Minutes: DD°MM.mmm’

• Degrees, Minutes, Seconds: DD°MM’SS.s”

• Use +/- or N, S, E, W to indicate East/West and North/South

• Online Converter:

– http://www.gpscoordinates.eu/convert-gps-coordinates.php

WGS84 / GDA94

• GPS System uses WGS84 as global datum – World Geodetic System from 1984

• All smart phone navigation apps are using WGS84, too. Some offer conversions to local datums.

• Australia uses GDA94 as regional datum

• There is little actual difference between WGS84 and GDA94

The Earth – A Perfect Sphere?

No, not really…

GDA94 vs WGS84

Global/Regional Datums(Spatial Reference System / SRS)• “A datum is a system which allows

the location of latitudes and longitudes (and heights) to be identified onto the surface of the Earth - ie onto the surface of a ’round’ object.”

• Local or Regional Datums“This diagram represents the Australian Geodetic Datum which was created in 1984 (AGD84 or AGD). Note how the Ellipsoid/Spheroid has been ’placed’ over Australia to best identify longitude and latitude. If you used this datum in the northern hemisphere longitude and latitude would be very poorly identified on the surface of the Earth.”

Coordinate Notations - Example-37.819552,144.947197

Coordinate Notations, cont’d

• Many Online Converter Sites, e.g. at http://www.gpscoordinates.eu/convert-gps-coordinates.php

What Are GPX Files?

GPX Files

• GPX = GPS eXchangeFormat

• Standard file format to exchange location data

• Can contain:– Waypoints: Manually saved

points of interest– Track points: Automatically

(periodically) recorded positions of where you walked

GPX Data Example

<trkpt lat="-37.96664058" lon="145.30062233"><ele>72.29</ele><time>2013-08-

04T04:33:02Z</time></trkpt>

<trkpt lat="-37.96670236" lon="145.30063564"><ele>72.33</ele><time>2013-08-04T04:33:08Z</time></trkpt>

<trkpt lat="-37.96676915" lon="145.3006414"><ele>72.43</ele><time>2013-08-04T04:33:14Z</time></trkpt>

GPX Data Example II

• A GPX file does not necessarily contain time and elevation data for track points.

• If the track points don’t have elevation information, elevation gain / loss cannot be calculated from the GPX file itself

• If the track points do not have timestamps, then duration of the walk and speed (average, max, min) cannot be calculated

• From the difference between two trackpoints, distance and direction can be calculated

GPX Precision

• Depends on frequency: how often are track points recorded by application?

• How many seconds between recordings?

• How much distance between recordings?

• Error correction mechanisms: application can choose to ignore track points which are in all likelihood incorrect

Where to Find GPX Files / Walks?

Walk Directories Victoria

• Where2Walkhttp://www.bushwalkingvictoria.org.au/walks-directory/

• Trailhiking Australiahttp://www.trailhiking.com.au/

• Open Spaces (Daywalks around Victoria, etc.)http://osp.com.au/?page_id=1006

• Other…

• Search the Web – but never trust the results, always try to verify reliability of data!

Where 2 Walk – Bushwalking Vic

Trailhiking

How To View/Modify/Create GPX Files?

Online/Web Tools

• GPSies

• GPSVisualizer

• MapMyHike

• and many others – search the web!

GPS Visualiser

Map My Hike

GPSies

PC (Windows/Mac/Linux) Tools

• GPS Tracks Editor

• Viking GPS

• and many others – search the web!

PC: GPS Track Editor

PC/Mac/Linux: Viking GPS

So What's Your Problem with the Elevation?

Elevation & Digital Elevation Model

• GPS by design is highly inaccurate when it calculates elevation for a point

• Hence: You can never trust elevation data which is just gained from GPS signal

• Most online mapping tools are using DEM data to determine the elevation of track points and the overall elevation gain/loss for the track

• DEM stands for: Digital Elevation Model• Some Smart Phone Apps use DEM data as well: they

allow you to download DEM data for a specific area (e.g. the Android App Orux). Disadvantages: this uses a fair amount of storage space on your phone.

DEM: SRTM I

• SRTM is one of several possible DEM data sources for mapping applications. There many other sources for different regions of the world, but a lot of times they are not available to the general public, and in a lot of cases they only cover limited areas of the world or a country.

• SRTM is the most commonly used DEM data source for mapping applications today.

• The Shuttle Radar Topography Mission (SRTM) was an international research effort that obtained digital elevation models on a near-global scale from 56°S to 60° N

• The elevation models are arranged into tiles, each covering one degree of latitude and one degree of longitude, named according to their south western corners.

• https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission

DEM: SRTM IIExample for SRTM elevation tiles.

DEM data is available for download at: https://dds.cr.usgs.gov/srtm/

Elevation Gain/Loss

• Calculating elevation data for a GPX track from DEM sources like SRTM is more art than science.

• The result will never be fully precise

• Even when applied to the very same GPX track data, different applications will provide you with different results – depending on the DEM source data they use and depending on how they calculate averages and how much “smartness” they apply to their algorithm.

• For the very same GPX track, Runkeeper gives 496m as total elevation gain, GPS Visualizer 525.6m and GPSies435m.

Runkeeper: 496m

GPS Visualizer: 525.6m

GPSies: 435m

GPS Smartphone Apps

GPS Enabled Apps

• SatNav: Turn-by-turn navigation

• Compass

• Location Sharing

• Navigation

Turn-By-Turn Navigation (Driving)

So that you get to the starting point of your walk – these apps are available for Android and iOS:

• Google Maps

• HERE Maps – Recommended (Free of charge, can download maps per country for offline usage)

• TomTom

• Many others

Fitness/Tracking Applications

• Enable you to record activities / tracks• Upload of tracks to “social” web site, view tracks• Share with friends, set goals, etc.• Examples:

– Runkeeper, – MapMyRun, – MapMyHike, – Nike+, – Runtastic, – Strava Run, – and many more

• Export GPX tracks later• NOT suitable for navigation!

Example Fitness App: Runkeeper

Current Position and DirectioniPhone Compass App Android: GPS Status

Current Position

• Compass Apps will provide you with your current location

• Most of them allow you copy your location coordinates so that you can paste them into another application (text message, email, etc.)

• Even if you rather use a printed map for navigation –sometimes it can be extremely helpful to just identify your current position on your phone/GPS device so that you then can identify your position on the map, using the geo coordinates grid system printed on all walking maps.

Location Sharing• Glympse is an location sharing application for Android and iOS. A big advantage: the one you

are sharing you location with does not need a specific application or device to view your location – any web browser will do.

• Apple iOS 8 and higher offer the functionality to share your location with anyone you are having a text message conversation with.

• Many “Chat” applications like WhatsApp also allow to share your current location.

Navigation Apps

Typical functionality of navigation apps:• Determine your position• Show your position on a map• Download / import maps for offline usage• Record the tracks you walk• Keep record of all your activities• Navigate to a destination (waypoint)• Follow a recorded track• Display a trip computer• Share you position with others• Share track with others

Should You Rely on Your Smart Phone for Outdoor Navigation?

Difference Between Navigation System and Smart Phone?

• Smart Phone is a multi-purpose computer, is neither shock-proof nor water-proof, has a very high power consumption, etc.

• A handheld Navigation System is specialised in outdoor navigation, the better models are shock and water proof, will work for several days before running out of power, have multiple antennas for better reception, special algorithms to handle the multipath problem, etc.

Can I Rely on a Outdoor Navigation System then?

• Always take laminated (protected), printed maps

• Compass

• If walking far away from civilization, take a PLB – Personal Locator Beacon

Navigation Apps / Map Viewer Examples:

• Android:

– Orux Maps – Free. Highly recommended!

– Avenza PDF Maps – Free

– Gaia GPS

• Apple iPhone

– GPS Motion X, about $2.50. Highly recommended!

– Avenza PDF Maps

– Gaia GPS

Map Data

• Online only:– Google Maps– Apple Maps– Microsoft/Bing– HERE Maps

• Open Street Map – comes in different flavours, but all based on OSM map sources:– OSM Street– OSM Topo– Mapnik– Etc.

• Topology Maps: e.g. VicMaps

• Any print map – scanned and calibrated

VicMap Topographic Maps

Scan & Geocode Maps

• Take any printed map to OfficeWorks and get it scanned in high resolution.

• OfficeWorks have large scanners, they can scan very large maps!

MAPC2MAP2

Use MAPC2MAPC to geo-calibrate scanned map file

Scan & Geocode Maps

• You can then export the geo-calibrated image file in different formats, suitable for different navigation apps

• Screenshot shows example of scanned Wilsons Prom app in Avenza PDF Maps

Thank You!