Managing geolocation and GPS

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Overview
Implementing the GPS management
Checking whether the GPS is enabled
Be notified when the GPS status changes
Position tracking
Ending the use of GPS functions
Implementing geolocation tracking
Overview
Principle and implementation
Operation according to the mode of use of the application
When to use each function?
Functions available according to the platforms
Summary table

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WEBDEV

WINDEV Mobile

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Managing geolocation and GPS

Overview

WINDEV Mobile and WEBDEV allow you to exploit geolocation and GPS features found on mobile devices and browsers.

In phone applications, you can:

Get information about the last known location of the device.
Ask to be notified when the device comes near a specific area.
Find out the current location of the device.
Retrieve an address.
...

Remarks:

The Map control is used to view a location. For more details, see Map control.
You can also track the user's location, even when the application is closed. For more details, see Implementing geolocation tracking.

In the Web sites, you have the ability to interact with the GPS features of the device, if available (mobile device in most cases). You can retrieve or track a location in a website displayed on a mobile device.

Caution: Geolocation is only available on certain modern browsers:

FireFox from version 3.5,
Chrome from version 5.0.342.1,
Opera from version 10.6,
Safari from version 5.0.

During the call to a geolocation function, the browser requests a location authorization.

Implementing the GPS management

Checking whether the GPS is enabled

To check whether the GPS is enabled, all you have to do is use GPSStatus.

Example:

// Is the GPS enabled?
IF GPSStatus() = gpsEnabled THEN
Error("The GPS cannot operate.", ...
"It must be enabled to access this application.")
EndProgram()
END

Be notified when the GPS status changes

To be notified when the GPS status changes, simply call GPSStatus and specify the name of the procedure that will handle the current GPS status.

Example:

GPSStatus(_ChangeOfGPSStatus)

The procedure code is as follows:

PROCEDURE _ChangeOfGPSStatus(Status)

IF CurrentStatus = Status THEN RETURN
CurrentStatus = Status
EndTimerSys(TIMER_RETRIEVAL)
SWITCH Status
CASE gpsEnabled
// The provider was enabled by the user.
STC_Status = "GPS enabled"
CASE gpsDisabled
// The provider was disabled by the user.
STC_Status = "GPS disabled"
CASE gpsOffService
// The provider is off service.
STC_Status = "GPS off service"
CASE gpsUnavailable
// The provider is temporarily unavailable.
STC_Status = "GPS unavailable"
CASE gpsAvailable
// The provider is available.
STC_Status = "GPS available"
// Requests location tracking with a maximum time between two calls to
// GPSFollowMovement(_GetLocation, 1000)
OTHER CASE
END

In this procedure, if GPS is enabled, a specific procedure is used to track the device.

This feature is not available.

Position tracking

To track the device's location, simply use GPSFollowMovement and specify the name of the procedure that will handle location changes.

Example:

GPSFollowMovement(_GetLocation, 1000)

The code of the procedure can be as follows:

PROCEDURE _GetLocation(MyLocation)
// Update the information about the location
// Latitude and longitude
STC_Latitude = StringBuild("Latitude: %1", MyLocation.Latitude)
STC_Longitude = StringBuild("Longitude: %1", MyLocation.Longitude)
// Speed
IF MyLocation.SpeedValid = True THEN
STC_Speed = StringBuild("Speed: %1 m/s", MyLocation.Speed)
IMG_SPEED_VALIDITY = IMG_OK
ELSE
STC_Speed = "Speed: N/A"
IMG_SPEED_VALIDITY = IMG_NOTOK
END
// Altitude
IF MyLocation.AltitudeValid = True THEN
STC_Altitude = StringBuild("Altitude: %1 m", MyLocation.Altitude)
IMG_ALTITUDE_VALIDITY = IMG_OK
ELSE
STC_Altitude = "Altitude: N/A"
IMG_ALTITUDE_VALIDITY = IMG_NOTOK
END
// Direction
IF MyLocation.DirectionValid = True THEN
STC_Direction = StringBuild("Direction: %1 ° E", MyLocation.Direction)
IMG_DIRECTION_VALIDITY = IMG_OK
ELSE
STC_Direction = "Direction: N/A"
IMG_DIRECTION_VALIDITY = IMG_NOTOK
END
STC_Last_update = StringBuild("Last update on %1 at %2.", ...
DateToString(MyLocation.MeasurementDate.Date), ...
TimeToString(MyLocation.MeasurementDate.Time))
STC_Last_update.Visible = True

In this code, MyLocation is a geoPosition variable. The properties of this type of variable are used to find out the location characteristics.

The WLanguage procedure used requires specific parameters.

Ending the use of GPS functions

Depending on the selected settings and on the call frequency, geolocation functions can consume a lot of resources on the device (battery, bandwidth, etc.). GPSEnd must be called when the location functions are no longer used by the application.

This feature is not available.

Implementing geolocation tracking

Overview

On a mobile device, you may need to track the user's location even when the application is closed or in the background.

You should be able to set up tracking while using as little resources as possible, especially when it comes to battery. This can be achieved by reducing accuracy, compared to standard GPS tracking.

Principle and implementation

To manage location tracking:

Enable location tracking with geoTrackingEnable.
Define the procedure called when changing the location with geoTrackingProcedure. This function must be used in the initialization process of project.

You can:

Disable location tracking with geoTrackingDisable.
Get the tracking status with geoTrackingStatus.

Caution: This location tracking has low precision. The events are sent only if significant changes of location occur and at time intervals exceeding several minutes. For information, the sending conditions per platform are as follows:

The events regarding the change of location are not sent if the location did not change by more than 500 meters, or if the time interval is less than 5 minutes (December 2014).
Location change events are sent at intervals that range from 30 seconds to 10 minutes, depending on the distance between locations.

For a more precise tracking, you must use GPSFollowMovement. However, this function:

requires the application to be started,
requires the application to be in the foreground,
consumes more battery.

Operation according to the mode of use of the application

If the application is already running, the procedure given to geoTrackingProcedure is automatically called when a location event is received. Any operation of application can be performed in this procedure.

When the application is stopped, if a location event is received, the application is restarted in the background. The "Initialization" event of the project is run, then the procedure specified in geoTrackingProcedure.

iOS limits the operations that can be performed when the application is started in the background. Therefore:

The execution of background operation cannot exceed ten seconds.
No window can be opened and no interface can be displayed (however, a notification can be sent).

Reminder: To determine if the application has been started in the background, use ExeInfo with the exeLaunch constant. The exeGeoTracking constant will be returned if the application was started in the background.

When to use each function?

Function	When to use it?	Accuracy	Energy consumption

geoTrackingXXX	Permanent tracking of location changes, even when the application is in the background.	High accuracy, but the frequency of notifications is low and varies depending on the system.	Low
GPSFollowMovement	Permanent tracking of location changes when the application is in the foreground.	Accuracy according to GPSInitParameter.	Consumption according to GPSInitParameter.
GPSDetectPosition	Notification of the proximity of a given location when the application is in the foreground.	Accuracy according to GPSInitParameter.	Consumption according to GPSInitParameter.
GPSGetPosition	Get current location at a specific moment when the application is in the foreground. It may take long, depending on the surroundings (inside a building, cloudy day, etc.).	Accuracy according to GPSInitParameter.	Depends on the number of calls.
GPSLastPosition	Immediately get the last known location of the device.	Low consumption, since it depends on when the last location was actually retrieved. Also depends on GPSInitParameter.	Low consumption.

Functions available according to the platforms

Summary table

The table below presents the different geolocation/GPS functions and the different platforms for which they are currently available (this table can evolve with each version):


Functions	Android	iPhone/iPad	Universal Windows Platform App	Browser code
geoAzimuth	X	X
geoDistance	X	X	X
geoGetAddress	X	X
geoGetArea	X	X		X
geoRunApp	X	X
geoTrackingDisable	X	X
geoTrackingEnable	X	X
geoTrackingProcedure	X	X
geoTrackingStatus	X	X
GPSDetectPosition	X		X
GPSEnd	X	X	X
GPSFollowMovement	X	X	X	X
GPSGetPosition	X	X	X	X
GPSInfo	X		X
GPSInitParameter	X	X	X
GPSLastPosition	X	X	X	X
GPSStatus	X	X	X	X
GPSStopDetection	X		X

Related Examples:

Cross-platform examples (WINDEV Mobile): WM Geolocation

[ + ] This example explains how to perform proximity searches with geolocation :
- search around me
- search in a city, at a given address, or close to a specific address.
The results are displayed in a looper and in a map with markers.