Navigating the Battlefields with Google Earth, GPS and British Trench

[WhiteStarLine]

"Slow ... slower ... Stop!"

A quick glance at the laptop and Google's flashing position indicator confirms the GPS has placed us on the front line of the right hand platoon of D company, 23rd Battalion AIF in July 1916 as they prepare for a brigade night attack. We park the car at the Pozieres town cemetery, where the left hand of the assault formation stretched to. I glance over where the right hand platoon of the battalion should have been and locate the place drily referred to as 'the second e in cemetery'. It is in a mature cornfield and immediately I see a shell sitting by the side of the road.

Picking up the laptop, I walk along the road towards Thiepval, following the path of my wife's great-great uncle who still lies in this field. Google tells me we have reached the 1st objective, a communication trench. The war diary records a non-standard trench map reference, so I'm not 100% sure and I detour along the track near Tulloch corner. Some unidentified ordnance, a crushed mess tin and an entrenching tool lie by the freshly-ploughed fields. The 23rd was told to stay and dig in after the right hand battalion fell back, so this spade would reasonably have belonged to an Australian soldier. I pick it up and return to the road, following the GPS towards the Thiepval Memorial, until the position indicator puts me astride the ridgeline, the objective taken and held with such sacrifice. Or as the 1918 Battlefield Souvenir put it, "the lads did splendidly in this unique operation".

Touring the battlefields with Google Earth & Trench Maps is a technique available to anyone with a laptop and GPS, or Android device. It is flexible, fast and for anyone who already has a laptop and GPS, free. You don't need an internet connection (we did over 2,000 km without one) and if you plot in advance the trench map references, you don't even need the trench maps themselves (pros and cons are discussed shortly).

The technique has been field tested in Flanders and Northern France on positions lying within Sheets 28, 36, 57d, 62d and 62b.

So, what do you need?

* Laptop;

* Power source;

* GPS;

* Internet connection.

Any laptop is fine, including a netbook. I was going to take a netbook as backup, but space limitations flying from Australia prevented this. The small screen of the netbook is actually perfectly adequate. Take note that if you are in the car for more than a few hours, your laptop battery needs charging. I took an inverter with me as my older laptop is power sensitive. Our hire car shipped with the higher efficiency cigarette plug sockets but when we used a tour guide, I could not power the laptop from her van. So, test before you go.

Google Earth supports GPS units from Garmin and Magellan, but my no-name Taiwanese sports GPS worked perfectly. Just test it first, as a later one I have doesn't connect due to Google's strict adherence to an older communications protocol standard. Commercial software such as GPSGate may fix this. When ready, simply start Google Earth, click 'Tools-GPS' and after clicking on the 'Automatically follow the path', check-box, click on the Start button. A blinking circle and the word 'Position' appears, updating every 4 seconds. Once again, test before you go!

Google states that any 2010+ Android device will run Google Earth and I assume these techniques apply perfectly, but I have not personally tested them. A fully compliant Android device includes a GPS.

So how did we do 2,000 kilometres without internet? Well, that is not exactly true as we made sure that every B&B we stayed at had wireless internet. Each night, I simply ran what Google calls a 'tour', visiting the places I wanted to go the next day by double-clicking on the Placemark icon. For a longer drive, such as Amiens to Abbeville or Zonnebeke to Pozieres, I clicked on 'Directions To Here' and clicked on each route segment. This simple routine ensured that Google Earth had the latest satellite imagery stored on my computer. When I walked down the slope towards the Somme, following a brigade HQ location in the woods, when the blinking icon told me I was there, I could compare the imagery with what I could see myself.

To optimise this part, set your cache in Google to the maximum value allowed. In 'Tools-Options-Cache', set the memory and disk values to 1024 and 2000.

I would have preferred to have an internet connection, but we received conflicting advice in Australia. Some told us that you could only purchase a data SIM with a valid French bank account. While in France, others told us that you need only turn up and show identification. Assuming the latter is correct, I would always recommend an internet connection while touring.

Where do you source the trench maps you need?

There are numerous sources for these. I typically use the McMaster series as the licensing allows for personal use. To match a Google map tile with a British Trench map, I find that we have to compromise and I divide the map into segments. Remember we are forcing together a British imperial grid system, a Belgian metric map, an obscure French projection system, a modern compromise projection and American tiled map software. Our map sources are often historic printed paper copies that once saw field use, then were stored in a museum, then scanned. I extract a square that covers exactly one letter, using image editing software (Microsoft Paint is perfectly adequate) to trim the trench map into a JPG. For example, I take the Beaumont-Hamel trench map 57d. I find the letter 'R' that covers roughly 5km x 6 km north of Pozieres, Courcelette and Thiepval, up to Miraumont. Save this file as a JPG. Then, in Google, click 'Add-Image Overlay' and select the JPG to import. Then click 'Convert to LatLonQuad' and put in the co-ordinates for each corner. Once done, out in the field the Google slider can be used to change how opaque (how much or how little of Google Earth imagery appears underneath the trench map). The placemarks and Google's GPS position indicator always appear over the trench map and you can have everything in between from just the trench map visible to just the satellite imagery.

How do you convert trench map references into Google placemarks?

Simply lookup the latitude and longitude for the trench map reference, which must be in the format such as 57d R 33 a 30.80. To avoid ambiguity, sub grid references should be in hundredths (ie a3.8 is written as a30.80).

Trench map or Google Imagery? Which is best?

I used both and each has its pros and cons. Once I had confidence that I was being guided to the right location, I tended to look at the placemark superimposed over contemporary imagery only. For example, tracing a trench raid at Messines, we pulled up where the 43rd Battalion raiding party first entered German lines. I pointed out a slightly larger potato plant as a reference to the start of the German posts. My wife nodded politely. I then turned around to two large modern farm buildings just behind us and indicated where the raid party had left their own lines. My wife was astonished at just how close the Allied and Germans were. In general, looking at the placemarks was all I needed. However, on the Hindenburg Line at Bony, where there is no indication that anything other than farming has ever taken place, I found that ability to look at the trench systems and barbed wire obstacles marked on the trench maps to be useful. In some locations, such as the steep banks of the Somme, the contours on the trench maps were needed to make it obvious why an observation post was located there. With the trench map option, the GPS told me where I was and orienting the laptop with trench map helped me try to understand what was once there. I noticed that the trench maps, being scanned versions of historic maps once carried into battle, showed darkened or yellowed paper and had poor contrast. In bright sunlight, this made them harder to use. A pristine trench map would be useful or the image could be digitally enhanced to boost contrast before importing into Google Earth.

How do you source Trench Map / Google Earth correlation points?

Once again, simply lookup the latitude and longitude for each corner of your chosen map. These have all been calculated and are made available free of charge. Every sheet, letter, numbered square and sub grid has its own latitude and longitude. The original technique defined a high-precision trench map reference as resulting in a positional accuracy of one hundredth of a 500 yard grid, or an area of around 21 square metres. Reversing this almost 100 years later strives for 'church-yard accuracy', placing the control point of a church spire on a trench map as being within the same churchyard and for 50% of cases on the church building itself.

Did you consider any other options?

Years ago I used OziExplorer and I considered using this with the IGN maps or with raw trench maps. I also got as far as downloading the FalconView moving map application, which is free and also seems to have a good reputation. In the end, Google won me over as I could practise every technique in Australia including georeferencing maps, overlaying images, testing their accuracy and running with a GPS. With the other two, I might have arrived in France and found some issue or error that stopped the GPS displaying my location or showed me in a slightly different position. However, these products might overcome two annoyances with Google Earth: Firstly, refresh seemed a bit slow. I forgot to change the polling interval and the default of 4 seconds seemed to take approximately 10 seconds in realtime. This meant that as we neared the location, we had to slow right down to a walking pace, which was no big deal. The other was that while Google Earth allows tremendous flexibility with zooming in and out, the GPS display takes over and shows a fixed scale at each update. This made looking ahead awkward, unless you temporarily stopped the regular position update.

So, in summary touring with Google Earth is fast, flexible, free and field-tested and I would have no hesitation in using the approach again.

Currently, the referred techniques are classed as 'experimental' until they have been independently verified by 12 - 15 users. Not every grid letter has been checked and I know I have the odd transcription error at sheet corners or boundary overlap. These are irritating and are fixed as I find them. Once verified, the instructions and associated data will then be placed in an online location so that they can be downloaded, free of charge.