A-GPS Tracker

Instruction and documentation

R Batzinger

OVERVIEW

Logo

What is the A-GPS Tracker App?

  • A-GPS Tracker can manage your position and altitude using the A-GPS capabilities of your phone.
  • Once track recording is started, it will and monitor your path
  • It stays active even when the phone goes to stand-by or you are use the phone for other applications.
  • Maps come from Google Maps but only when the device is online.

A-GPS Tracker was designed for hikers

  • want to record a new path
  • want to follow an existing track
  • want to avoid loosing their return way.

Tracker Features

  • user geo-coordinates are given in real time:

Elevation: is given in meters and is relative to Mean Sea Level .Note that most android programs are only giving the raw data provided by GPS ,i.e. height relative to a geocentric reference ellipsoid (WGS84 ). Latitude and Longitude coordinates are given both in degrees and in UTM-WGS84 (used in some published paper maps).

A Track can be displayed on the map, recorded, stored or loaded to/from phone memory and shared with other people.

Points Of Interest( also called Waypoints) can be added to your track.

The Elevation vs Distance profile of a track can be shown on the screen.

Statistics of a loaded GPX track will include, among the others, the calculated net walk time, ascent and descent altitude.

A “Follow Path” monitor function can be enabled to get an alarm in case you are leaving a pre-loaded GPX path.

Take Photographs and see where the photos were taken on the map.

A-GPS Tracker is designed and normally works well on most Android devices, does not consume much battery power and you can leave it active for hours. With a limited number of phone types the App may not work and you will need to change your phone settings. If the path acquired shows long straight lines, this is the symptom that the device is not working correctly: the phone is set to power saving, pausing, or stopping the App when it is not displayed on the screen. In this case see Troubleshooting.

A-GPS Performance

GPS is used here as a generic term and refers to the capability to receive position data from signals received from satellites. Modern phones can obtain position data from more than one satellite system, i.e. not only the american GPS but also GLONASS, BeiDou and Galileo. A-GPS Tracker will receive data from all the supported and available satellite navigation systems; in addition A-GPS (Assisted GPS) also uses ground sources like cell tower data and WiFi, that may enhance quality and precision when in poor satellite signal conditions and in particular will help to reduce time to start fixing initial position.

GPS will be the source of the more accurate position: Latitude, Longitude and Altitude. Altitude provided by GPS is corrected (EGM96) to obtain altitude relative to mean sea level.

Note that for hikers Altitude it is of particular importance and can be given only by GPS. GPS may get poor position coordinates when GPS signals are weakened by meteorological conditions and may lead to significant errors in urban areas, when satellite signals may be reflected by buildings and therefore are received from a multi-path propagation.

A-GPS gives precise position and altitude when:

  • you are in a open sky place,
  • your phone antenna is not obstructed by metallic objects, buildings or mountains
  • meteorological conditions are sufficiently good.

The initial GPS lock

  • requires the view of a several satellites at the same time
  • a good lock will result in elevation data
  • (elevation data is the least precise of GPS data
  • initially it may be quite inaccurate, but the continuous acquisition of new data will correct the initial readings

GPX Files

A GPX File is a XML data format File, written according to the GPS Exchange Format for the interchange of GPS data (waypoints, routes, and tracks) between applications and Web services on the Internet.

The GPX file created by AGPS-Tracker has no references to photographs. The photographs are independent of the file and have embedded data related to the location and time of the shot.

CONTROL BUTTONS

Compass indication button

Normally the map is oriented north. By pressing this button, the map will be oriented in the direction indicated by the Compass. This is not present on phones that do not have the right sensors, i.e. magnetometer and gravity.

GPS quality button

GPS is enabled and the signal is good! High precision geocoordinates will be sampled continuously. Recording of your path can run smoothly.

Center Map Button

Push this button if you want your position (blue circle) in the center of the map.

Map Type Selector

Pushing this botton you will be asked to select the type of map that you want to see. Default is Terrain.

The view of the map needs an internet connection. Map viewing is not required to track your path.

Photograph GIS

By pressing this button you can take a picture. The relative symbol will be shown on the track.

Track Recorder Function

This will open the Track Recorder window with the following buttons:

REC/STOP to start/stop and restart the recorder. Note that actual recording will start only if high precision geolocation coordinates and altitude will be available. SAVE to save into a GPX file the path that you have been walking so far. RESET to cancel your current path.

Add point of interest

This button appears only when the Track Recorder has started to sample your position. With this you can add a Point Of Interest marker to your track.

Comparison to previous track

This button appears only when an existing GPX file has been loaded. Push this button if you want the loaded track to be shown in the center of the map. When this is pushed, statistics relative to the loaded track are shown on a scrollable window.

Elevation indication

This button will open another window showing the Elevation vs Distance profile. In this graphic drawing window you can tap a point on the graph and see also its position on the Map and the other way round.

Progress indication

Pushing this button you can see an icon moving on the map from the start to the end of the loaded track.

Off-track alarm

When this button is checked the phone will generate an alarm when the distance from the loaded track and the user position is larger than 30m. Alarm will generate a beep and a warning message.

TROUBLESHOOTING

A-GPS Tracker is designed to remain active when the phone goes in stand-by. But some phones try to kill apps that are show a continuous power consumption. This behaviour can normally be disabled but unfortunately it is nested in the various settings of the phone and can be different for manufacturers, models and Android versions.

Possible Remedies

  • Disable any Power saving for the phone( Settings parameters or dedicated energy saving apps)

  • Disable energy saving optimisations for A-GPS Tracker.

  • https://dontkillmyapp.com/ contains specific instructions for various phones and manifactures.

This worked for me

  • Go to system Settings > Battery.
  • Go to High background power consumption.
  • Find your app in the list and enable the high battery consumption.

Today’s exercise

MAP

Things to note:

  1. Compare the quality of the breadcrump tracings. Which mobile was the most accurate?

  2. Compare the accuracy in various regions:

    • such as openspaces, among buildings, under trees, straight runs

  3. Do the following techniques improve the quality of the readings or not? Why?

    • Averaging multiple readings
    • Least mean square estimate of a line

Group Assignment

Write a series of slides to summarize your findings in a 5 min presentation.

Explain what you learned about the accuracy of GPS.

Compare your waypoint calculation with those of Google map.

Does averaging multiple tracing improve the quality of GPS?