Geotagging

Blogging has not been happening much of late for me. The Christmas period was great but did not involve much reflection on education. Since returning to work the pressure has been enormous.

Anyway, I have to lead a seminar on geotagging this Friday at a SICTDG event in Stirling, This post gives a summary for those who are there of where I got my sources. You might find it easier going straight to Wikipedia if you want some more detailed information. THe purpose of the post is to provide answers to the "how" of geotagging and not to consider the educational applications, of which there are many!



What is Geotagging?
This is the process of adding geographical identification metadata to media This data usually consists of latitude and longitude coordinates, though it can also include altitude, bearing, and place names.

Latitude is the angle at the centre between any point on the earth's surface and the plane of the equator. The north pole 90° N; the south pole 90° S. Longitude is the angle east or west, at the centre between any point on the earth's surface and the plane of an arbitrary north-south line between the two geographical poles. The line passing through Greenwich is the international zero-longitude reference line.

Traditionally, degrees have been divided into minutes and seconds There are several formats for degrees, all of them

DMS Degree:Minute:Second e.g. N49°30'00"
DM Degree:Minute e.g. N49°30.000'
DD Decimal Degree e.g. N49.5000°

To convert from DM or DMS to DD

decimal degrees = D + M/60 + S/3600

Different systems use different formats!

How do I Geotag Media?
Before lokking at the practicalities it is worth making sure that we understand what GPS does. GPS stands for Global Positioning System. A typical GPS receiver calculates its position using the signals from four or more GPS satellites. The receiver uses four measurements to calculate the 4 variables - x, y, z, and t. Most receivers will then turn this into latitude and longitude.

Automatic Tagging
Some digital cameras support GPS and record the time and location of the photographer each time a photo is taken.
A photo's relevant GPS data is stored in the photo's EXIF file. An external GPS unit, can be also be sued. The date and time clocks of both the GPS unit and the digital camera must be synchronized. Specialised software is then used to pull the two together later.

EXIF stands for Exchangeable image file format . The metadata tags within the EXIF data cover a broad range of things including:
date and time
camera settings
thumbnail
descriptions and copyright information.
location information

Manual Tagging
If the user knows the coordinates, the location can be manually added using software such as Flickr. It is also possible to tag a picture by dropping it on Google Earth.

There are two methods of geotagging in Flickr. Photographs can be dragged onto a map or specific location tags can be added manually.

geotagged
geo:lat=latitude e.g. geo:lat=51.4989
geo:lon=longitude e.g. geo:lon=-0.1786

There are also other tags which can be used when linking Flickr photos with Google Earth using a script such as FlickrFly.

These include:
ge:head=xxxx e.g. ge:head=127.00, where xxxx is the view heading in decimal degrees (0-360) where zero is looking North.

ge:tilt=yyyy e.g. ge:tilt=60.00, where yyyy is the view tilt angle in decimal degrees, where 0 is looking straight down and 90 is looking horizontally from ground level.

ge:range=zzzz e.g. ge:range=560.00, where zzzz is the range of the viewpoint in metres from the marker location.

The script to add to a Flickr comment in order to go directly to the location on Google Earth is:

<a href="http://www.roblog.com/flickrfly.kml">Fly to this location </a> 

 using < a href="http://www.roblog.com/flickrfly-docs/">FlickrFly < /a> 

 (Requires < a href="http://earth.google.com/">Google Earth < /a>)

There a few sites that might be of interest if you want to get geotagging:

www.geograph.org.uk - This is the site that got me started thinking about tagging images to locations. A game to try to cover the map of Britain with photod.

www.flickr.com - where all my photos goes online.

earth.google.com - where to go to download Google Earth.

www.roblog.com/flickrfly-docs - the flickr fly script for use in flickr in combination with Google Earth.

www.wikipedia.org - where I got most of the info for the presentation.

www.geocaching.com - a site for those as sad as me who want to use their GPS for something else!

www.mediafire.com/?evjtjbiwklx - this is where I have put the powerpoint file from the seminar.