GeoTagging

What is GeoTagging

GeoTagging, sometimes referred to as Geocoding, is the process of adding geographical identification meta data to various media such as websites or images. The data usually consists of latitude and longitude coordinates, though it can also include altitude and place names.  Etrex

This involves using a GPS to log a track of your walk and then using this information to tag the photographs with the position where it was taken. Sounds complicated? Not really, all that is done is that the date/time the photograph was taken is compared to the date/time of the way points in the GPS track, once a match is found the way point lat/long values are written to the EXIF header of the JPG file.

What is the point of it

Try this other web site of mine http://www.flickr.com/photos/tferenc, simply geotagging the photograph and up loading it to the web site shows the photograph on a map.

Alternatively the JPG filename can be renamed to include the date and location it was taken e.g.'IMG_1337 2006-12-02 SK 11980 60980.JPG', just outside Hartington, Derbyshire. It is then obvious where and when it was taken, or use XnView to put the file name onto the photograph.

How do I do it

The assumption is made that you do not have any software to do this. The links to the software can be found on this page.

  1. Use G7toWin to upload the track from the GPS.
  2. Save this as a GPX file (GPS Exchange File).
  3. Start NDWGeotag.
  4. In the 'Set-up' page.
  5. Add the GPX track.
  6. Specify the Photographs directory.
  7. Configure the Offset, in minutes, i.e. the difference the GPS Track and Photograph taken time.
  8. Make sure OSGB is selected.
  9. Save your configuration.
  10. Press GeoTag.
  11. Click parse to see what GPS data has been added.
  12. If required click Rename to rename the photograph to contain the OSGB and/or date in the file name.

Hint

The GPS stores the date/time values using GMT so I have set my camera to GMT as well. The main problem when GeoTagging is figuring out what the time offset is between the GPS and the photograph. To find out exactly at what time the photo was taken use exiv2. But once this has been done it is always the same, unless the camera adjusts the time automatically when the clocks change!

What next


MapThe photographs can be placed on line for everyone to view using Flickr or a web site like ours to display the track and the photographs, but we would strongly suggest using NDWGeoTag, at least, to rename the JPG files so that the date and location are part of the name. Therefore everyone will know exactly where and when the photograph was taken. What is the accuracy? We would say the error is less than 5m. from our tests using a 1:25000 map.

What does it cost


All the software/web sites mentioned here are either free ware or the web sites mentioned have a free option, some of the software was written by us. All that has to be purchased is a data cable for the GPS to link it to the PC. Mine was bought via Ebay it cost about 8 inc. p&p, just make sure the cable is correct, i.e. Serial or USB. Or of course you could make your own.

This software is for Windows, but we have found the odd bit of Mac software, see below. Also we have written some Linux scripts to do this as well.

Software Required

To get started, only G7ToWin and NDWGeotag are required, both free ware.

Program Description
   
G7ToWin our current favourite
WWMX Location Stamper A Microsoft research tool that GeoTag the JPG files using the GPX file.
NDWGeoTag Our own program to parse the GPX file to add OSGB data to the photographs,
There is no installation program, just unzip all the files into a directory of your choice.
exiv2 This is used by NDWGeotag and is included in the zip file. It is a DOS/Console application that displays all the Exif data in the JPG file. The -pt option is the one to use.
Renamer Renames files. Very handy to change the IMG portion of the name or if the files have been renamed incorrectly, during testing always use a copy of the photographs.
Syz
PFranc
Pinouts
Make your own data cables.
XnView A superb program for viewing and converting bitmaps,can be used to batch convert a group of files, to do things like writing the file name onto the photograph.

Mac Software


Program Description
   
MAC Geotagger 1.2 Mac GeoTagger


Acronyms


Acronym Description
   
EXIF Exchangeable Image File Format
GMT Greenwich Mean Time
GPS Global Positioning System
GPX GPS Exchange Format
JPG Graphics file type/extension (lossy compressed 24bit color image storage format developed by the Joint Photographic Experts Group)
Lat Latitude
Lon Longitude
OSGB Ordnance Survey Great Britain
Serial Serial (RS232) Communications port
SUB Universal Serial BUS


Specifications and Libraries etc.

Ignore these unless you want to write your own software or you want some really technical information or software.

Program Description
   
EXIF Exif Specification
GeoTrans A US military Geographic Translator for Windows, this translates co-ordinates system, very comprehensive!
GPX GPS Exchange Format Specification
Proj.4 Cartographic Projections Library
JScoord JavaScript and PHP libraries for lat/long OSGB conversion
http://www.nearby.org.uk/ On line co-ordinate conversions



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