Location-Based-Services (LBS) for iPhone and iPad

May 2, 2012, By Jeff Miller

Do you know where you are? Your iPhone 4/4S and iPad might! Incorporated into Apple’s iOS operating system are a set of services called – Location Based Services (LBS). LBS uses a combination of your iDevice’s GPS (if it has a GPS) and/or WIFI-positioning to pin-point your location, track your movements, and when used in combination with the mapping services provided by iPhone/iPad operation system -iOS – display your location.

To see if your iPhone/iPad is using LBS go into “Settings” and bring up “Location Services”:

Here, on an iPhone 4S, we see that LBS is on and a list of the application registered to use LBS. Notice that the Camera and Camera+ applications are in this list. The camera applications will attach the location of where you take a picture into the saved photo image.

LBS will work on WiFi-only iPad devices too:

iPhones have a built-in GPS chip. The iPhone operating system and services use “assisted GPS” (aGPS) to enhance the performance of location-based tasks. Roughly speaking, aGPS uses a combination of GPS, cell-phone tower locations, and WiFi-positioning to track locations.

WiFi-positioning is determined by using a database of locations for WiFi hotspots and signal strength measurements from those hotspots to your device.

The iPhone 4/4S and iPad 2/3 with 3G/4G have both aGPS and WiFi-positioning support. The iPod Touch 4th generation and WiFi-only iPad only support WiFi-positioning.

When you take a picture with a camera application on an iPhone 4/4S,iPad – with LBS on for the device and the camera application (e.g. Camera/Camera+/Instagram)  – the camera application will use the “Core Location” Application Programming Interfaces (API) within iOS to get the current latitude and longitude coordinates of the device’s location. The latitude/longitude coordinate pair is called a “geo-coordinate”.

iPhones/iPads store the picture’s geo-coordinates in a portion of the file, in which is photo is saved, called the Exif section. Exif is a standard developed for TIFF based images – that is also used for images saved in JPEG and other formats.

Application’s can use various iOS APIs, including the “Assets Library”, to extract the geo-coordinates from a picture and display the location of where the picture was taken on a map and/or display near-by places/businesses.

Geo-tagged photo in Camera+:

In my next column – we will continue our investigation of Location-Based Services and examine the iPhone’s map functionality.


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