The State of GPS Data from Mobile Devices
Most of the mobile devices today support GPS geo tagging. In fact most of them come bundled with navigation software that uses GPS and therefore all the pictures and (maybe) videos can be geo tagged. But as expected different vendors come with different support and formats.
Even more – until recently Symbian didn’t support any geotagging before the installation of an additional software – such as Location Tagger . So generally the things are quite simple:
- iPhone OS geotags both video and image files;
- Android geotags only images;
- Symbian geotags only images – and on some devices this is possible only after installing a software;
This is in breve the state of mobile device geotagging!
Why Use GPS Data?
Perhaps one of the main reasons why not support geotagging especially on video files can be the usage of those geo tags. First of all what a geotag means?
You may know that even Android doesn’t “geotag” videos this is not quite true. Because after using you gallery you can see where those videos are shot. This is fantastic, but actually the real information about where the video has been taken is not into the video file, but it’s in an additional log file that keeps it. Thus actually the video files doesn’t know the geo coordinates.
Here comes the problem with video format, because you cannot be sure that every format supports tags that can keep geo coordinates. Actually quicktime’s MOV can store them, while Symbian’s 3GP cannot. In fact Symbian cannot store any geo information about video files!
So now we’ve at least three different formats for each of those three vendors.
- quicktime for iPhone
- mpeg-4 with Android
- 3gp with Symbian
For now I can only say that iPhone can keep the geotag into his video files.
But let me return to the question – why we need this geo tags? Until the video file is on the mobile device – there’s no problem. But once you try to download it – whether on Flickr, YouTube, Picasa, etc. you’ll lose any geo information if it’s not into the file tags. And of course if the above sites can’t read it!
The general reason to store this data into the file is to move it along with the file. Once you move this file from your mobile device to a web platform you’ll see where the file has been created.
EXIF, Exiftool and PHP’s exif_read_data
There are several tools to read geotags. For images, and here we talk only for JPEGs, this is the EXIF information. You can download the exif command line program and try to reed data with it:
Which can result in something like that:
Manufacturer |Nokia Model |E71 Orientation |top - left x-Resolution |300.00 y-Resolution |300.00 Resolution Unit |Inch YCbCr Positioning |centered Compression |JPEG compression x-Resolution |72.00 y-Resolution |72.00 Resolution Unit |Inch FNumber |f/3.2 Exif Version |Exif Version 2.2 Date and Time (origi|2011:01:24 12:15:01 Date and Time (digit|2011:01:24 12:15:01 ComponentsConfigurat|Y Cb Cr - Aperture |3.20 EV (f/3.0) Light Source |0 Flash |Flash did not fire, auto mode. Focal Length |4.9 mm FlashPixVersion |FlashPix Version 1.0 Color Space |sRGB PixelXDimension |2048 PixelYDimension |1536 Custom Rendered |Normal process Exposure Mode |Auto exposure White Balance |Auto white balance Digital Zoom Ratio |1.00 Scene Capture Type |Standard GPS tag version |0x02, 0x02, 0x00, 0x00 North or South Latit|N Latitude |42.00, 39.00, 24.67 East or West Longitu|E Longitude |23.00, 21.00, 28.45 Altitude reference |0x00 Altitude |625.50
While for video files (iPhone) exif cannot help you, this is possible through Exiftool. With it you can read even iPhone video geotags:
In addition this information can be read with PHP via exif_read_data:
$info = exif_read_data('filename.jpg'); var_dump($info);
And this will give you not only standard tags, but geo tags too.