Article

Geotagging

Geotagging, also sometimes but not often called geocoding, is the practice of adding geographical identification information into the photographs metadata. This may be done at the time the photo is taken, may be done soon after based on other information captured at the same time the photographs were taken or could be added later.

So why would we want to do this:-

• To identify points while on a walk, along a cliff, down a  river or canal, around a town or city.

• Perhaps to be be certain which, of several similar items, we photographed, for example wind pumps (windmills) in some areas of the Norfolk broads.

• After a holiday to know where each picture was taken (this works worldwide).

• To resolve questions in your mind about where the picture was taken or even where you were stood when you photographed it.

• To be able to show that you were on a public right of way, when you took that picture of a National Trust property they now want a share of your income on, now it's been published.

You could also use it to tell breakdown services where you are to get rescued, providing you also have a mobile phone. When abroad it may allow you to fix your current location on a map.

This is a long page, and may take a couple of reads to completely make sense to you, but I think its well worth the effort, as Geotagging is starting to become more common, and there are, as you will see, low-cost as well as expensive ways to achieve this.

How we Geotag

There are a number ways to do this, in an accurate and automated way at the time the photo is taken or soon after, based upon GPS (about 32 global positioning satellites). Usually this will record the latitude and longitude, plus a very accurate time and a height above sea level. With systems that contain a digital compass the direction that you are pointing can also be recorded, but this is rare.

Dedicated Bluetooth receivers interfacing GPS data into camera. This is a similar sized unit to the dedicated geotagger, but the GPS information is coming from a separate GPS unit in your pocket. A cable from the unit is connected to the camera. You need both a camera that can accept the information as above plus a separate GPS that sends information via Bluetooth and can be set to give out the right sort of data required. The manufacturers of each of these devices say which GPS units it will work with.

Interface cable and GPS unit. The GPS unit may be in your pocket or perhaps on a stand clipped to the camera or to the camera strap. Cables to devises in your pocket are inconvenient to use, and that's putting it politely. On the camera strap is better, or on the camera.

The logic in taking the last two approaches is that you may already have a suitable GPS unit. If you were going out to get something specific then a dedicated geotagger would be more convenient.

Capture GPS track and add to card before images are uploaded. There is a small device about the size of a matchbox, that records your location over time. This runs in your pocket. Having taken your photos, you take the card out of the camera and plug it into this small unit, and using the time it can add the Geotagging information into all of the photographs. The cost is small, quoted as $100.

Capture GPS track and add via special software on your computer. This is a similar technique but uses the facility built into some GPS/satnavs to record a track. This information can be uploaded to a computer.  A special program, some freeware, some shareware, can then be used that compares the time on the photographs with the satnav GPS track and adds the Geotagging information. If you already have or buy a cheap second-hand GPS with this capability then this is the lowest cost route. The disadvantage is that you have to keep the information and actually run this.

In addition you can use some mapping systems and software to find the locations and add the Geotags later. This is of course far more prone to error.

Manual retagging

There are a lot of mapping systems and add-ons for mapping systems that allow you to get the longitude and latitude, there are also look up tables showing many places and many places and topics contain Geotagging information within Wikipedia.

Overcoming difficulties

Battery Power

Some ways of achieving Geotagging can be heavy on batteries.

• When a GPS is sending a stream of data to a camera, the camera remains at least partly on even when turned off.
• Most dedicated Geotagging and Bluetooth receiving devices pull theire power from the camera.

This can have a huge affect on the number of photographs you can take before the battery is flat.

In order to extend the battery life some, but not all, units have special modes. The Geopic II for example, a dedicated Geotagging device powered from the camera, has normal, battery saver and freeze modes. They say typical battery counts are 1750 images per battery without the device connected, 1690 with it in freeze mode, 970 in battery saver mode and 315 in normal mode.

Inside buildings

Few if any GPS units will work if they don't have obstructions between them and the sky. They can see (receive radio from) up to 20 satellites to get their fix, but need to be able to see at least 3. Similarly some large buildings, especially some reflective ones, can be a problem and cause the fix to be lost.

Some units automatically give the last good fix they had, some others have a freeze mode that allows you to lock a reference. Some try to predict where the unit is now from its last position and last few minutes direction, this is useful in car systems to get through short tunnels and the like.

Accuracy

Different map projection systems may produce small differences, it's quite common when out and about to find small differences between the maps and ground, either brought about by the ground shape, surveying corrections, and from mapping a part of a round planet onto flat sheets. Also in some new or developing areas there may have been provisional information that was used, and other changes and construction that has occurred and not yet put on the map. Its also difficult when online to know how old a map or aerial photograph is. So not all errors we discover will be the Geotagging.

From what I have read I think its held within the RAW Exif data simply as degrees, gong to 5 decimal places, and the other displays we see, is the result of the software reading it, so we get to see the same picture giving slightly different output in different editors or viewers.

It would also appear from published information that the accuracy of GPS is within about 50ft, or 15 metres, although part of the scientific backup of Wikipedia says 7 metres. My GPS I use on the car is considerably more accurate than that, at a guess I would have thought 2 to 3 metres at the most, when I drive thorough a roundabout it shows what appears to be the exact place in the layout, not 50ft away. The accuracy in part depends on how many satellites are visible, and generally the more there are, the more accurate it should be. It may be software within the unit that can then average out or track  it to get closer. There are military systems using some additional or different satellites that are far more accurate, but these systems are not used in the commercial products we buy. At any time there are about 32 satellites in use, some working more accurately than others, although they do give out a confidence rating amongst the information they are transmitting base on known land positions. Although you need a minimum of 3 satellites to get a fix, the more you can see the better the position. About 5 is needed to get any reasonable accuracy. Weather and a wide range of other factors also affect it, large reflective buildings may also cause errors in readings.

With most camera units I think its sampling, so as you move about it could be fractionally behind your current position, but near enough for all practical purposes.

Some of the tests I have done using my GeopicII geotagger on a D300, and comparing the position on maps have been close but in some cases up to several hundred yards away from where I was stood, when I have looked the position given up on a map. This is close enough to allow me to know one location from another, but not to say what side I photographed an item from or similar. Is the error in the system, conditions, on the maps, or am I expecting too much from the technology we have available at this point. Having only recently spotted the errors on some photos I now need to run a more in depth test and comparison with my car satnav, and several mapping systems to get to the bottom of this. ---- So check for or watch out for another article on this soon.

New equipment becoming available

In the same way as we have new cameras out each year, we see more Geotagging solutions coming out. This is in some ways still very much a developing area. Nikon for example have a device, Nikon GP1 its shown  on this link page, and can be pre-ordered in Hong Kong currently for £650 plus carriage but not yet available.  You can find it on the UK Nikon site under accessories/SLR/Data. Based on the Hong Kong price which is usually a lot less than buying in the UK, this looks like being expensive. AJ Purdy has it listed but say 'price to be announced', and not available yet. The Geopic II Geotag for the Nikon camera, which I have and came out in October 2007 is £176 including VAT. The Photofinder, a device that keeps track of your position then you stick in your camera card and using the times, updates the images to include the Geotagging information, was said to be going to be $100, (£50-£70) when announced, but I haven't seen one yet, in theory one of these would work with just about any camera.

We are working on another page that will include links to each supplier, analysis of prices and more, but we haven't managed to track down all the information yet to complete this, so watch the newsletter for it to be announced when complete. This will also include software and other solutions as well.

Now you have the data, what next

There are a range of GPS formats in existence, most just representing different ways to write the same information and to different levels of accuracy. In effect different numbers of decimal places. Some of these were defined in Wikipedia, other variations on this you will come across, but from these will generally makes sense.

On a Nikon camera using the metadata, we get 2 formats displayed in the Nikon software, and on the camera. For example on one of my photos it shows  Latitude N51° 27.874'  (51° 27' 47.1")  Longitude  W3° 9.921' (3° 9' 55.3") Altitude 11.00m. This is a statue in Cardiff Bay. Loading this photo into Photoshop Elements and looking under file/fileinfo/advanced and then expanding the Exif data it shows Latitude 51,27.874N Longitude  3,9.921W Altitude 11/1 it also tells me this was based on seeing 7 satellites. From this you can see information is not always represented the same. In neither system can I do anything directly with this, I can't edit it, or copy it. We will come back to editing software a little later on this page.

From what I have read I think its held within the RAW Exif data simply as degrees, going to 5 decimal places, and the other displays we see is the result of the software reading it, so we might get to see the same picture giving slightly different output in different editors or viewers.

From the information on accuracy above you can see there may be other considerations as well.

Finding the position on maps

If we go to Google maps and put in the search field from above N51° 27.874' W3° 9.921', it shows the page and a place tagged nearby.

A simple to use calculator and display tool is at boulter.com/gps/ when I entered N51° 27.874' W3° 9.921', it gave me the same in several other formats, including straight degrees and decimals that a number of systems use. The page also includes a section of a Google map with the location marked. Also below the map is a lot of links to different mapping systems, putting in the parameters and displaying these for you. I have experimented with entering the information in a range of formats and it worked it out in each case correctly USE THIS TO MAKE OTHERS BELOW EASIER TO USE.

There is a page on a website at www.nearby.org.uk/coord-ll.cgi that allows you to enter the latitude and longitude and converts this to a whole series of links to a variety of mapping systems as well as giving you an Ordnance Survey grid reference. The page does not always work, but I think this is because the server is overloaded and timing out, so try again and it most likely will.

Multimap. As far as I can see you can't enter latitude and longitude coordinates directly into Multimap, although you can create a link using them, which you could also do by changing the page address in your browser. It appears to take only one format, and this is the RAW format that unfortunately most software don't show, so you will have to use a converter first to get this.  Multimap say:-

To link to a map using latitude and longitude coordinates, please use the following URL: http://www.multimap.com/maps/?lat=51.5154&lon=-0.1452&zoom=16. Simply change the lat and lon coordinates value within the URL each time to produce a valid map. You also have the option to select your most preferred zoom level. The zoom levels available are from 1 to 18 (1 being the furthest away and 18 being the closest).

Streetmap can take Latitude and longitude in its search and there is a button to indicted that is what you are entering. They explain the format for the search as

So N51° 27.874' W3° 9.921' is perhaps entered entered as N27:27.874,W03:09.921, but this does not work, it also doesn't work if I take the decimals out. The other format I have N51° 27' 47.1 W3° 9' 55.3 should in theory be entered as N51:27:47,W03:09:55, this does work and produces a map showing a point not far away.

Image storing systems

If you add photos to flicker it uses Geotagging either on the image or you can manually select to add them. With flicker you can make your images visible to only you, to those you choose or to everyone. You can also look on the flicker map page and see what images are geotagged already to that area. It also shows the latitude and longitude of the cross on the screen, so is useful for manually Geotagging images. You can see this at flickr.com/map

A number of other storage systems and some of the bookmarking systems  can also store Geotagging information.

From editing software to maps

I can't find anything in Photoshop Elements, beyond being able to read the location, Capture NX2 likewise shows the location data only. I have been told these will both work with other software to link to maps, but I haven't yet worked out how.

In the future, I would expect that all viewing and editing software will have a button that when pressed gives you a choice of what mapping system you want to see the location and then provide it. The component parts to do this are already available, it just needs to be included.

Where we have reached

Wikipedia, Flicker and a variety of other sites make a lot of use of Geotagged information, but at the moment for us to use it directly from our photographs is still not that easy, mostly because there is no standardised way to display or  enter the information, and instructions and ease of use is still poor. You can use it, but its a struggle.

I would suggest that starting from Google maps   or  boulter.com/gps/ is the easiest route for the present time.

We have two other pages we are working on, but is not yet available, one looking in detail at accuracy, the other looking at the range off equipment with links to suppliers, and more. We may also break up this page into several and expand each section. What do you know, what is your experience of Geotagging, let us know.